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Star Motion

North

LOOKING SOUTH

JUNE | SOUTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

monthly sky guide

special events JULY

PHASES OF THE MOON

FULL MOON NEW MOON The strong man of Greek mythology, Hercules, lies overhead as seen from
mid-northern latitudes, between the bright stars Vega (in Lyra) and Arcturus (in
2006 11 July 25 July Boötes). South of Hercules is another large constellation, Ophiuchus, which
2007 30 July 14 July represents a man encoiled by a serpent, Serpens. In southern skies, the Milky Way
2008 18 July 3 July branches overhead from the southwest to the northeast.The zodiacal constellations
2009 7 July 22 July Scorpius and Sagittarius stand high in the Milky Way’s richest part.
2010 26 July 11 July
2011 15 July 1, 30 July
2012 3 July 19 July

PLANETS NORTHERN LATITUDES

2007: 1 July Venus and Saturn are 0.7° THE STARS of the sky, the stars of the Summer good binocular sights.The globular
apart in the western evening sky. Triangle climb ever higher, while clusters M13, in Hercules, and M5,
Overhead lies Hercules, which is a the Square of Pegasus appears in the head of Serpens, remain
2007: 20 July Mercury is at greatest large but not particularly striking closer to the eastern horizon. well positioned this month.
morning elongation, magnitude 0.5. constellation. Its most distinctive
feature is a quadrangle formed by Low in the south are the rich THE SUMMER TRIANGLE
2008: 1 July Mercury is at greatest four stars, called the Keystone. constellations Scorpius and Deneb (left), Vega (top), and Altair (right)
morning elongation, magnitude 0.6. North of Hercules lies the Sagittarius.This is the best month form a prominent triangle that remains
lozenge-shaped head of Draco, the for northern observers to see the visible well into autumn in northern skies.
2008: 9 July Jupiter is at opposition, Dragon. Between Draco and the two most southerly zodiacal figures
magnitude -2.7. north celestial pole is the bowl of in the evening sky.
the Little Dipper, in Ursa Minor.
2008: 10 July Mars and Saturn are 0.6° DEEP-SKY OBJECTS
apart in the western evening sky. Arcturus, in Boötes, remains
prominent in the western sky. Ophiuchus, the large constellation
2010: 30–31 July Mars and Saturn are Spica, in Virgo, is lower in the between Hercules and Scorpius,
1.8° apart in the western evening sky. southwest, and the Plough dips contains numerous globular
clusters, although only two of
2011: 20 July Mercury is at greatest low in the northwest. In them, M10 and M12, are of any
evening elongation, magnitude 0.5. the eastern half note.The most impressive deep-
sky objects in Ophiuchus are the
2012: 1 July Mercury is at greatest 9AM
evening elongation, magnitude 0.5. open clusters IC 4665 and
NGC 6633, both
2012: 1–2 July Venus and Jupiter are
4.8° apart in the eastern dawn sky. 6AM

ECLIPSES

2009: 21–22 July A total eclipse of the
Sun is visible from India, China, and the
Pacific Ocean. A partial solar eclipse is
visible from eastern and southeastern Asia,
Indonesia, and the Pacific Ocean.

2010: 11 July A total eclipse of the Sun
is visible from the southern Pacific Ocean.

3AM
MIDNIGHT

THE NIGHT SKY URANUS NEPTUNE MORNING SKY

july

SOUTHERN LATITUDES

THE STARS conditions.The Lagoon Nebula

The curved tail of Scorpius and (see p.241), or M8, an elongated

the asterism known as the Teapot, gas cloud containing the star

formed from the main stars of cluster NGC 6530, can be seen

Sagittarius, are virtually overhead well through binoculars.To the

for southern observers.The Milky north, in Serpens Cauda, the tail of

Way is particularly dense and the Serpent, lies the cluster M16 –

bright towards Sagittarius and visible through binoculars –

Scorpius because this is the view embedded in the much fainter

towards the centre of the Galaxy. Eagle Nebula (see pp.242–43).

Alpha (α) and Beta (β) Other famous deep-sky objects

Centauri – Rigil Kentaurus (see in Sagittarius, such as the Trifid

p.248) and Hadar – are in the Nebula, M20 (see p.244), need to

southwest, pointing down to Crux, be seen through a telescope.

the Southern Cross. Spica (in However, one particularly bright

Virgo) is in the eastern sky, patch of the Milky Way, M24, is

Arcturus (in Boötes) in the prominent to the naked eye. In

northwest, and Vega (see p.249), in adjoining Scorpius, the bright

Lyra, is in the north. Altair (see open clusters M6 and M7 remain

p.248), in Aquila, is high in the high in the sky.

northeast, and observers about

30°S or closer to the equator can METEOR SHOWER

see Deneb, in Cygnus, low in the The Delta Aquarids, the best

northeast. In the southeast, 1st- southern meteor shower, is active

TOWARDS THE CENTRE OF THE GALAXY magnitude Fomalhaut, in Piscis in July and August, reaching a peak

The centre of the Galaxy cannot be seen directly, Austrinus, enters the scene. around 29 July. At best, perhaps 20

because it is obscured behind the dense Milky Way DEEP-SKY OBJECTS meteors an hour can be seen
star fields of Sagittarius and Scorpius. The exact radiating from the southern half of
centre is thought to be marked by an intense radio Sagittarius is well stocked with Aquarius, but they are not
source called Sagittarius A* (boxed). outstanding deep-sky objects, particularly

among them the 5th-magnitude bright. NOON

POSITIONS OF THE PLANETS globular cluster M22, which
is visible to the naked
This chart shows the positions of the planets in July from 2006 to 2012. The planets are represented eye under good
by coloured dots, while the number inside each dot denotes the year. For all planets apart from

Mercury, the dot indicates the planet’s position on 15 July. Mercury is shown only when it is at 3PM
greatest elongation (see p.64) – for the specific date, refer to the table, left.

Mercury Mars Saturn Neptune

Venus Jupiter Uranus

EXAMPLES Mars’s position on 15 July 2009. The arrow indicates that
the planet is in retrograde motion (see p.64)
Saturn’s position on
15 July 2009

MIDNIGHT 9PM

THE NIGHT SKY

EVENING SKY

BOOTE M92 LYRA Deneb M29
CYG
M3 HERCULES

C S NUS
VE
WEST M6B4 ECROEMNAICESNAATNICEIS M101 DRACO M39 PEGASUS
M51 URSA MINOR
M87 CERTA
Mizar LA EAST
LEO

LEO THE PLOUGH CEPHEUS M52 PISCES
MINOR M81
URSA MAJOR ANDROMEDAM31
Polaris CASSIOPEIA
M34 TRIANGU
M103 869 ARIE N O R T H ELUM
NGC
M33
NGC 884

NORT LYNX CAMELOPARDALIS PERSEUS S
CaGsEtoMr INI AST
Capella
HW
EST

AURIGA

M38 OBSERVATION TIMES

NORTH Date Standard Daylight-
time saving time
LOOKING NORTH
15 June Midnight 1am
JULY | NORTHERN LATITUDES 1 July 11pm Midnight
15 July 10pm 11pm
1 August 9pm 10pm
15 August 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N Zeniths
Variable Galaxy Globular Open Diffuse Planetary 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

452 THE NIGHT SKY

PEGASUS CYGNUS Vega LYRA M13 BERECNOICMEAMS53

M15 EQUULMEU2 Albireo M57 CBOORROENALIS A
BOOTES
VULP
M27 SAGIT Altair Arcturus

DELPHINUS TA ECULA HERCULES VIRGO

EAST AQUARIUS S PUT M104 WEST
SERPENSMC5A
AQUILA Spica CORVUS
LIBRA
SCEARUPDEANS M12 LUPUS

M10
M14
M30 M11 HYDRA
OPHIUCHUS CENTAURUS
APUISSCTIRSINUS SCUTMU26M
ECLIPTIC M16
M25
CAPRICORNUS M17
M18
M24 M23 M9 M83

M22 M8 M80
M19 Antares M4
SAMG5I5TTARIUS M28 M21

MICROSCOPIUM M54 M7 M6 M62
HEAST
M69

Shaula

T AUCSOTRROANLIAS W
SOU TELESCOPIUM EST
SOUTH
INDUS NORMA

ARA

Star Motion

PAVO North

SOUTH

LOOKING SOUTH

JULY | NORTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N Zeniths
Variable Galaxy Globular Open Diffuse Planetary 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY 453

OBSERVATION TIMES

Date Standard Daylight-
time saving time

LOOKING NORTH 15 June Midnight 1am
1 July 11pm Midnight
JULY | SOUTHERN LATITUDES 15 July 10pm 11pm
1 August 9pm 10pm
15 August 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

Star Motion

North

LOOKING SOUTH

JULY | SOUTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

456 monthly sky guide

special events August

phases of the moon

full moon new moon The Summer Triangle formed by the bright stars Vega (in Lyra), Deneb (in Cygnus),
2006 9 August and Altair (in Aquila) lies on the north–south celestial meridian in the northern sky
2007 28 August 23 August this month.The cross-shaped figure of Cygnus, the swan, stands out against the
2008 16 August 12 August background of the Milky Way, which passes overhead in mid-northern latitudes. In
2009 6 August 1, 30 August the southern sky, the rich Milky Way star fields in Sagittarius and Scorpius, towards
2010 24 August 20 August the centre of the Galaxy, remain well placed for observation.
2011 13 August 10 August
2012 2, 31 August 29 August
17 August

planets Northern latitudes

2006: 7 August Mercury is at greatest THE STARS Ophiuchus remain well placed in Dumbbell, the easiest such object
morning elongation, magnitude 0.2. the southwest, and Arcturus, in to see through binoculars. Another
2006: 27 August Venus and Saturn are Blue-white Vega (see p.249), in the Boötes, is lower in the west. In the celebrated planetary nebula, the
0.1° apart in the eastern dawn sky. constellation Lyra, is the first bright east, the Square of Pegasus leads Ring Nebula (see p.253) or M27,
2009: 14 August Jupiter is at opposition, star to appear overhead as the sky the stars of autumn into view. in Lyra, can be found with a
magnitude -2.9. darkens on August evenings. Next telescope.The Wild Duck Cluster,
2009: 24 August Mercury is at greatest to Lyra is Cygnus, popularly DEEP-SKY OBJECTS or M11, in Scutum is a
evening elongation, magnitude 0.3. known as the Northern Cross.The 6th-magnitude open cluster visible
2010: 7 August Mercury is at greatest star at the head of Cygnus, Albireo, The August skies are stocked with through binoculars.
evening elongation, magnitude 0.4. is a beautifully coloured double deep-sky objects for northern
2010: 20 August Venus is at greatest star, easily divided by the smallest observers.The Milky Way is METEOR SHOWER
evening elongation, magnitude -4.3. of telescopes. South of Cygnus is divided by a dark dust cloud
2012: 15 August Venus is at greatest Aquila, the Eagle, from where the known as the Cygnus Rift, which The year’s top meteor shower, the
morning elongation, magnitude -4.3. Milky Way continues, via Scutum, extends southwestwards from Perseids, reaches a peak around
2012: 16 August Mercury is at greatest towards Sagittarius and Scorpius in Cygnus into Ophiuchus. South 12 August, although some activity
morning elongation, magnitude 0.3. the southwest. Hercules and of Cygnus, in the obscure can be seen for a week or so either
constellation Vulpecula, is the side of this date. Perseid meteors
eclipses 9AM are bright: at best, an average of
planetary nebula M27, one a minute can be seen streaking
2007: 28 August A total eclipse of the Capella popularly known away from northern Perseus. Most
Moon is visible from North and South Perseids are seen after midnight,
America, eastern Asia, and Australasia. 6am as the because Perseus does not rise high
2008: 1 August A total eclipse of the Sun
is visible from parts of Asia, Canada, and before then.
Greenland. A partial solar eclipse is visible
from Asia and parts of Europe. 3am
2008: 16 August A partial eclipse of the
Moon, visible from Australasia, Asia,
Africa, Europe, and eastern south America.

50°

40° Castor midnight

Pollux GEMINI TAURUS PLEIADES

30° 06 06 09 11 09 12 07
11 06 12 12
Aldebaran
HYADES 11
Mira
20° CANCER Betelgeuse PISCES

Procyon Bellatrix 10 AQUARIUS

0° 09

-10° Rigel

the night sky PISCES AQUARIUS

12 11 10 09 08 07 06 Fomalhaut

12 11 CAPRICORNUS
neptune
10 09

08 07

Perseid meteors CETUS 06
Mild nights in mid-August
are ideal for lying outside AQUARIUS
and watching members of
the Perseid meteor shower uranus
flash across the northern sky.

august 457

Southern latitudes

THE STARS year, such as the Lagoon Nebula
(see p.241), M22 in Sagittarius,
Sagittarius and its Milky Way star M16 in Serpens Cauda, and M6
fields remain high overhead, with and M7 in Scorpius. In addition,
Scorpius to the southwest of it. this month southern observers can
Alpha (α) and Beta (β) Centauri – see the Wild Duck Cluster (M11)
Rigil Kentaurus (see p.248) and in Scutum and, looking north of
Hadar – are low on the the equator, the Dumbbell Nebula
southwestern horizon.To the (M27) in Vulpecula, and the Ring
north are Altair (in Aquila),Vega Nebula (M57) in Lyra (see p.253).
(in Lyra), and Deneb (in Cygnus),
the stars that form the northern
Summer Triangle – this is the best
time of year to see them in the
evening sky from southern
latitudes.The Square of Pegasus is
rising in the northwest. Fomalhaut,
in the constellation Piscis
Austrinus, is high in the east, with
Achernar, in Eridanus, lower in the
southeast.The Small Magellanic
Cloud (see p.301) is visible
midway between Achernar and
the south celestial pole.
the night sky
DEEP-SKY OBJECTS the lagoon nebula in Sagittarius
09 09 09 09 09 09 09 09Among the dense star fields of the Milky
09 09 09 09 09 09 09 09The best deep-sky objects to viewWay lies the Lagoon Nebula (bottom, right),
in the southern sky on August also known as M8, in Sagittarius (right).
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09evenings are those that passed the
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09celestial meridian earlier in the

09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09POSITIONS OF THE PLANETS
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09
This chart shows the positions of the planets in August from 2006 to 2012. The planets are Sagittarius noon
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09represented by coloured dots, while the number inside each dot denotes the year. For all planetsThe Teapot asterism (bottom), formed by
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09apart from Mercury, the dot indicates the planet’s position on 15 August. Mercury is shown onlyeight stars in Sagittarius, is a familiar
when it is at greatest elongation (see p.64) – for the specific date, refer to the table, left. pattern in summer skies.

Mercury Mars Saturn Neptune

Venus 09 Ju0p9iter 09 09 0U9ranus 09 09 09

exam ples 3pm 40°
30°
09 09 09 09 Sat0u9rn’s po0si9tion on09 09 09 09 Ma0rs9’s posi0ti9on on 1059Augus0t92009. T0h9e arrow indicates
15 August 2009 that the planet is in retrograde motion (see p.64)

09 09 09 09 09 09 09

midnight

6pm

9pm Arcturus LEO 20°
10°
VIRGO Regulus 07 0°
-10°
Altair 12 08 08
12
QUARIUS CAPRICORNUS 06 Spica 09 06 10 07

09 08 OPHIUCHUS 10 08
malhaut 11 10 09
SAGITTARIUS
10

07 LIBRA
Antares

Shaula

SCORPIUS

evening sky

OBSERVATION TIMES

Date Standard Daylight-sav-
time ing time

LOOKING NORTH 15 July Midnight 1am
1 August 11pm Midnight
AUGUST | NORTHERN LATITUDES 15 August 10pm 11pm
1 September 9pm 10pm
15 September 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N Zeniths
Variable Galaxy Globular Open Diffuse Planetary 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

Star Motion

North

LOOKING SOUTH

AUGUST | NORTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N
Variable Galaxy Globular Open Diffuse Planetary Zeniths 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

OBSERVATION TIMES

Date Standard Daylight-
time saving time

LOOKING NORTH 15 July Midnight 1am
1 August 11pm Midnight
AUGUST | SOUTHERN LATITUDES 15 August 10pm 11pm
1 September 9pm 10pm
15 September 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

Star Motion

North

LOOKING SOUTH

AUGUST | SOUTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

462 monthly sky guide

special events September

phases of the moon

full moon new moon Northern nights grow longer as the Sun approaches the celestial equator, but in the
2006 7 September southern hemisphere the nights shorten. On 22–23 September, the Sun lies on the
2007 26 September 22 September celestial equator, and day and night are of equal length worldwide.The rich band of
2008 15 September 11 September constellations along the Milky Way, from Cygnus in the north to Sagittarius and
2009 4 September 29 September Scorpius in the south, begin to give way this month to fainter constellations, many
2010 23 September 18 September of them with watery associations, such as Capricornus, Aquarius, and Pisces.
2011 12 September 8 September
2012 30 September 27 September
16 September

planets Northern latitudes

2007: 29 September Mercury is at THE STARS Austrinus is low in the south with the North America Nebula, on
greatest evening elongation, magnitude 0.1. Aquarius above it. A cascade of account of its shape. Under clear,
2008: 6–7 September Mercury and Mars Cepheus, high up in the north, faint stars suggests the flow of dark skies, it can be detected with
2.5° apart in the western evening sky. is best placed for evening water from the water carrier’s urn binoculars, but it is best seen on
2008: 11 September Mercury is at observation this month and next. towards the southern fish, Piscis long-exposure photographs.
greatest evening elongation, magnitude 0.2. Its most celebrated star is Delta (δ) Austrinus. For observers at high Another object of note in Cygnus
2008: 11 September Venus and Mars Cephei, the prototype of a class northern latitudes, this is the best is the open star cluster M39, which
are 0.3° apart in the western evening sky. of pulsating variables. Deneb in time of year to see the zodiacal is visible through binoculars.The
2010: 19 September Mercury is at Cygnus,Vega (see p.249) in Lyra, constellation Capricornus in the 6th-magnitude globular cluster
greatest morning elongation, magnitude and Altair (see p.248) in Aquila, the evening sky, lying low in the south M15, also visible through
-0.1. stars of the Summer Triangle, to the right of Fomalhaut. binoculars, is not far from the star
2010: 21 September Jupiter is at remain high in the western half Enif – Epsilon (ε) Pegasi – which
opposition, magnitude -2.9. of the sky, while the Square of DEEP-SKY OBJECTS marks the horse’s nose in Pegasus.
2011: 3 September Mercury is at Pegasus is high in the east with
greatest morning elongation, magnitude 0.0. Cassiopeia between it and the Near Deneb in Cygnus lies one of
north celestial pole.The bright star the most distinctive nebulae in the
eclipses Fomalhaut (see p.249) in Piscis sky, NGC 7000, popularly called uranus

2006: 7 September A partial eclipse of 9AM 6am PISCES
the Moon is visible from Australasia, Asia,
Africa, and eastern Europe. 3am 12 11
2006: 22 September An annular eclipse
of the Sun is visible from eastern South 10 09
America and the southern Atlantic Ocean.
A partial solar eclipse is visible from South 08 07
America and western and southern Africa.
2007: 11 September A partial eclipse CETUS
of the Sun is visible from southern South
America.

Capella 06

AQUARIUS

Castor

30° Pollux GEMINI TAURUS PLEIADES ARIES
20° 11
10° 09 07 12 11

0° LEO 09 06 12 Aldebaran PISCES
-10° 07 11 HYADES
-20° 08 Regulus 07 CANCER 10
-30° 06 10 Bellatrix
Betelgeuse Fomalhaut

Procyon

Mira

the night sky Rigel

morning sky



the harvest moon
The full Moon that occurs
closest to the northern
autumn equinox is termed the
Harvest Moon, since its light
was said to assist farmers
working late in the fields.

september 463

Southern latitudes

DEEP-SKY OBJECTS THE STARS

Aquarius contains two famous Scorpius is low in the west, with
planetary nebulae, although neither Sagittarius and the densest regions
is particularly easy to find through of the Milky Way above it.The
small instruments.The Helix large northern Summer Triangle of
Nebula (see p.253), or NGC 7293, Altair,Vega, and Deneb is visible
is the nearest planetary nebula to in the northwest, while in the
us. Its size means that its light is southwest, Alpha (α) and Beta (β)
spread out over such a large area Centauri – Rigil Kentaurus (see
that clear skies are essential to p.248) and Hadar – are visible
glimpse it through binoculars or a from latitude 20°S and farther
low-power telescope.The Saturn south.The Square of Pegasus
Nebula, NGC 7009, is so named dominates the northeastern sky.
because, when seen through a large
telescope, it appears to have rings First-magnitude Fomalhaut (see
like the planet Saturn. A small p.249) in Piscis Austrinus is almost
telescope shows the Saturn Nebula overhead, along with Capricornus
simply as a greenish disc. and Aquarius. Achernar, the bright
star at the end of the celestial river
Also in Aquarius is the globular Eridanus, is high in the southeast,
cluster M2, which resembles a as is the Small Magellanic
fuzzy star when seen through Cloud (see p.301). A group of
binoculars.To the north of this is constellations with exotic names,
another globular cluster that can such as Phoenix,Tucana, Grus, and
be viewed through binoculars, Pavo, is spread across the southern
M15 in Pegasus. half of the sky.
the night sky
the small Magellanic Cloud POSITIONS OF THE PLANETS
This small satellite galaxy (left) appears beside 09 09 09 09 09 09 09 09
the globular cluster 47 Tucanae (right), which is 09 09 09 09 09 09 09 09
in the foreground ­in our own galaxy.
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09
neptune 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09This chart shows the positions of the planets in September from 2006 to 2012. The planets are
AQUARIUS represented by coloured dots, while the number inside each dot denotes the year. For all planets
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09apart from Mercury, the dot indicates the planet’s position on 15 September. Mercury is shown only
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09when it is at greatest elongation (see p.64) – for the specific date, refer to the table, left.

09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09MercuryMarsSaturn Neptune
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09Venus
12 11 10 09 08 07 06 09 09 09 09 Ju0p9iter 09 09 0U9ranus 09 09 09
exam ples

09 09 Sat0u9rn’s pos0i9tion on09 09 09 09 Ma0r9s’s posi0ti9on on 1059Septe0m9ber 200099. The arrow
15 September 2009 indicates the planet is in retrograde motion (see p.64).

09 09 09 09 09 09 09 09

CAPRICORNUS 30°
20°
3pm

9pm

6pm

Arcturus

Altair 10°

AQUARIUS CAPRICORNUS 10 09
11
10 08 OPHIUCHUS VIRGO 0°
06 -10°
SAGITTARIUS 07 12
Antares 10 11
Shaula 07
10 08 08
08

Spica

09 06
12
LIBRA -20°

Fomalhaut -30°



evening SCORPIUS

sky

OBSERVATION TIMES

Date Standard Daylight-
time saving time

LOOKING NORTH 15 August Midnight 1am
1 September 11pm Midnight
SEPTEMBER | NORTHERN LATITUDES 15 September 10pm 11pm
1 October 9pm 10pm
15 October 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N Zeniths
Variable Galaxy Globular Open Diffuse Planetary 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

Star Motion

North

LOOKING SOUTH

SEPTEMBER | NORTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N Zeniths
Variable Galaxy Globular Open Diffuse Planetary 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

OBSERVATION TIMES

Date Standard Daylight-
time saving time

LOOKING NORTH 15 August Midnight 1am
1 September 11pm Midnight
SEPTEMBER | SOUTHERN LATITUDES 15 September 10pm 11pm
1 October 9pm 10pm
15 October 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

Star Motion

North

LOOKING SOUTH

SEPTEMBER | SOUTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

monthly sky guide

special events OCTOBER

PHASES OF THE MOON

FULL MOON NEW MOON The Square of Pegasus takes centre stage in the northern skies in both hemispheres,
a sign of the arrival of the northern autumn and the southern spring. Northeast of
2006 7 October 22 October it lies the Andromeda Galaxy, the nearest large galaxy to the Earth. South of the
2007 26 October 11 October Square, a band of faint zodiacal constellations crosses the sky, from Aries in the east
2008 14 October 28 October to Capricornus in the southwest.
2009 4 October 18 October
2010 23 October 7 October
2011 12 October 26 October
2012 29 October 15 October

PLANETS NORTHERN LATITUDES

2006: 17 October Mercury is at greatest THE STARS p.249) in Piscis Austrinus is low on High in the north, M52, an open
evening elongation, magnitude 0.0. the southern horizon beneath the cluster near Cassiopeia, is visible
The Square of Pegasus lies high in stars of Aquarius. In the western through binoculars. Between this
2006: 31 October Mercury and Jupiter the sky from mid-northern sky, the Summer Triangle lingers, and the Square of Pegasus lies an
are 3.2° apart in the western evening sky. latitudes. From one corner of the while in the east Taurus leads the often-overlooked planetary nebula,
Square, the stars of Andromeda stars of winter into view. NGC 7662, nicknamed the Blue
2007: 14–15 October Venus and Saturn extend northeastwards towards Snowball. A small telescope is
are 2.9° apart in the eastern dawn sky. Perseus and Cassiopeia. Capella DEEP-SKY OBJECTS needed to see it.
twinkles above the horizon in
2007: 28 October Venus is at greatest Auriga, lower in the northeast. In October evenings are a good time METEOR SHOWER
morning elongation, magnitude -4.4. the north, the Plough is at its to view the Andromeda Galaxy,
lowest, and it is below the horizon M31 (see pp.302–303). It can be One of the year’s lesser showers,
2008: 22 October Mercury is at greatest for observers south of about seen as an elongated misty patch the Orionids, reaches a peak of
morning elongation, magnitude -0.4. latitude 30°N. with the naked eye, if skies are not some 25 meteors an hour around
too polluted, and it is easily visible 21 October.They radiate from
2009: 6 October Mercury is at greatest Directly beneath the Square of through binoculars, spanning a northern Orion, near the border
morning elongation, magnitude -0.5. Pegasus is a loop of stars known as greater width than the full Moon. with Gemini.This area rises late,
the Circlet, representing the body of
2009: 8 October Mercury and Saturn are one of the fishes in the zodiacal 6AM thus the meteors are
0.3° apart in the eastern dawn sky. constellation of Pisces. best seen after
Fomalhaut (see
2009: 13 October Venus and Saturn are 3AM midnight.
0.6° apart in the eastern dawn sky.

2011: 29 October Jupiter is at
opposition, magnitude -2.9.

2011: 30–31 October Mercury and
Venus 2° apart in the western evening sky.

2012: 4–5 October Mercury and Saturn
are 3.2° apart in the western evening sky.

2012: 26 October Mercury is at greatest
evening elongation, magnitude -0.1.

9AM MIDNIGHT

NOON

THE NIGHT SKY POSITIONS OF THE PLANETS

This chart shows the positions of the planets in October from 2005 to 2012. The planets are
represented by coloured dots, while the number inside each dot denotes the year. For all planets
apart from Mercury, the dot indicates the planet’s position on 15 October. Mercury is shown only
when it is at greatest elongation (see p.64) – for the specific date, refer to the table, left.

Mercury Mars Saturn Neptune

Venus Jupiter Uranus

EXAMPLES Mars’s position on 15 October 2009. The arrow THE SQUARE OF PEGASUS
indicates the planet is in retrograde motion (see p.64) This huge square in the northern autumn sky
Saturn’s position on is composed of three stars in Pegasus and
15 October 2009 one in Andromeda (top, left).

october

SOUTHERN LATITUDES

THE STARS that stands out is 1st-magnitude high in the north, the Square of DEEP-SKY OBJECTS
Fomalhaut (see p.249), almost Pegasus. Between Pegasus and
In contrast to the sparkling skies of overhead in the constellation Piscis Fomalhaut lies Aquarius, the Water Tucana contains the second-best
southern winter, the constellations Austrinus. In the northeast sky is Carrier. More constellations with globular cluster in the sky, 47
of October evenings are mostly Altair (see p.248) in Aquila and, watery associations fill the western Tucanae, or NGC 104, which is
faint and unremarkable. One star visible to the naked eye as a fuzzy
part of the sky – star and appears impressive through
FAMILIAR ASTERISMS Pisces, the Fishes; binoculars. It covers the same area
The Circlet of Pisces (left) and the Y- Cetus, the Sea of sky as the full Moon, near the
shaped Water Jar of Aquarius (right) Monster or the Small Magellanic Cloud, but it lies
are two easily recognizable star Whale; and Eridanus, much closer to us – about 15,000
patterns in the October evening sky. the River.The light-years away – in our own
constellation galaxy. On the edge of the SMC,
Eridanus ends at the NGC 362 is another, fainter
bright star Achernar, globular cluster, also in our galaxy.
high in the south.
The Small Magellanic October and November
Cloud (see p.301) is evenings are the best time for
lower in the south, southern observers to view the
with the Large Andromeda Galaxy, M31 (see
Magellanic Cloud pp.302–303), which lies low in
(see p.301) now on the northern sky. Near it is
view in the southeast. another member of our Local
Canopus in Carina Group of galaxies, M33, a smaller
is also visible in the spiral galaxy that is less easy to see.
southeast, for those In clear, dark skies, it can be
farther south of the glimpsed through binoculars or a
equator than 20°S. low-power telescope as a large,
rounded patch.

MIDNIGHT

URANUS NEPTUNE NOON
9PM 3PM

6PM

EVENING SKY THE NIGHT SKY

OBSERVATION TIMES

Date Standard Daylight-
time saving time

LOOKING NORTH 15 September Midnight 1am
1 October 11pm Midnight
OCTOBER | NORTHERN LATITUDES 15 October 10pm 11pm
1 November 9pm 10pm
15 November 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N Zeniths
Variable Galaxy Globular Open Diffuse Planetary 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

Star Motion

North

LOOKING SOUTH

OCTOBER | NORTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N Zeniths
Variable Galaxy Globular Open Diffuse Planetary 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

OBSERVATION TIMES

Date Standard Daylight-
time saving time

LOOKING NORTH 15 September Midnight 1am
1 October 11pm Midnight
OCTOBER | SOUTHERN LATITUDES 15 October 10pm 11pm
1 November 9pm 10pm
15 November 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

Star Motion

North

LOOKING SOUTH

OCTOBER | SOUTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

474 monthly sky guide

special events November

phases of the moon

full moon new moon Cassiopeia lies overhead for northern observers, as the
2006 5 November Milky Way runs from Cygnus in the west to Gemini in
2007 24 November 20 November the east.The large figures of Pisces, the Fishes, and
2008 13 November 9 November Cetus, the Sea Monster or Whale, are spread across the
2009 2 November 27 November equatorial region of the sky, while in the southern sky
2010 21 November 16 November the Large and Small Magellanic Clouds are high up.
2011 10 November 6 November
2012 28 November 25 November
13 November

planets Northern latitudes

2005: 3 November Mercury is at THE STARS the Double Cluster, embedded in the princess, hero, king, and queen
greatest evening elongation, magnitude 0.0. the Milky Way between Perseus Joined in Greek myth, Andromeda (right),
2006: 1 November Mercury and Jupiter All the main characters in the and Cassiopeia.The Andromeda Perseus (bottom), Cepheus (top), and
are 3.2° apart in the western evening sky. Perseus and Andromeda myth Galaxy, M31 (see pp.302-303), Cassiopeia (centre) appear together in
2006: 25 November Mercury is at greatest (see p.352) are on show in the remains high up this month. northern skies in November.
morning elongation, magnitude -0.3. November evening sky. Cetus
2007: 8 November Mercury is at greatest contains a remarkable variable star, meteor showers reaching a peak around 17
morning elongation, magnitude -0.4. Mira (see p.281). It is easily visible November. Usually no more than
2008: 30 November Venus and Jupiter to the naked eye when at The Taurids have a broad peak in 10 meteors per hour are seen, but
are 2° apart in the western evening sky. maximum brightness, every 11 the first week of the month, when surges of activity occur every 33
2010: 20 November Mercury and Mars months or so, but the rest of the around 10 meteors an hour may years or so. High activity is not
are 1.6° apart in the western evening sky. time it fades out of sight. High in be seen coming from the region expected again until around 2032.
2011: 1–14 November Mercury and the west is the Square of Pegasus, south of the Pleiades cluster.
Venus 2° apart in the western evening sky. with the stars of the Summer Although not numerous, the 3am
2011: 14 November Mercury is at Triangle lower in the northwest. meteors are long-lasting and often Midnight
greatest evening elongation, magnitude -0.2. bright. A second meteor shower in
2012: 27 November Venus and Saturn DEEP-SKY OBJECTS November, the Leonids, radiates Capella
are 0.5° apart in the eastern dawn sky. from the head of
Two open star clusters, NGC 457 Leo,
eclipses and transits and NGC 663, are easy to see with
binoculars in Cassiopeia. Even 6am
2006: 8–9 November The transit of better are NGC 869
Mercury across the Sun is visible from and 884, a pair
North and South America, the Pacific known as
Ocean, Australasia, and eastern Asia.
2011: 25 November A partial eclipse of 9AM
the Sun is visible from the southern Indian
Ocean and Antarctica.
2012: 13–14 November A total eclipse
of the Sun is visible from northeastern
Australia and the south Pacific. A partial
eclipse is visible from New Zealand, the
rest of Australia, and the Pacific Ocean.

noon Pollux Castor PLEIADES
12
CANCER GEMINI ARIES

09 07 05

Arcturus LEO 05 Aldebaran TAURUS Mira
10°
11 06 HYADES

07 Regulus Bellatrix

08 Betelgeuse

Procyon
09 09 09 09 09 09 09 09
0° 09 09 09 09 09 09 09 09 09

VIRGO 12 10 07 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09
-10° 07 11 Rigel
12 09 09 09 09 09 09 09 09 09 09 09 09 09 09
09 09 09 09 09 09 09 09 09 09 09 09 09 09
06 09 10
06 05 Spica 09 09 09 09 09 09 09 09 09 09
09 09 09 09 09 09 09 09 09 09
-20° LIBRA morning sky

the night sky POSITION S OF THE PLANETS
Th is chart shows the positions of the planets in November from 2005 to 2012. The planets are
-30°
represented by coloured dots, while the number inside each dot denotes the year. For all planets
apart from Mercury, the dot indicates the planet’s position on 15 November. Mercury is shown only
when it is at greatest elongation (see p.64) – for the specific date, refer to the table, left.

-40° Mercury Mars Saturn Neptune

Venus 09 Ju0p9iter 09 09 0U9ranus 09 09 09

-50° examples

09 09 09 09 09 Sat0u9rn’s pos0i9tion on09 09 09 09 Ma0r9s’s pos0it9ion on 0159 Novem09ber 200099. The arrow
15 November 2009 indicates the planet is in retrograde motion (see p.64).

09 09 09 09 09 09 09 09

November 475

Southern latitudes

THE STARS DEEP-SKY OBJECTS

Achernar, the bright star at the end South of the head of Cetus is
of Eridanus, lies high in the south M77, the brightest of the Seyfert
on November evenings.The other type of galaxies (see p.310).
stars of Eridanus extend to Orion, Seyferts are spiral galaxies with
which is rising in the east. unusually bright centres, caused by
Aldebaran and the stars of Taurus hot gas spiralling around a massive
are in the northeast, and the black hole. A telescope is required
Square of Pegasus is high in the to see M77.
northwest. Aquarius is in the west,
with Fomalhaut (see p.249) in In the south, the globular
Piscis Austrinus in the southwest. cluster 47 Tucanae is still on view
The Large and Small Magellanic near the meridian.The Large
Clouds (see p.300 and p.301) are Magellanic Cloud, with the
high in the south. Brilliant Tarantula Nebula, NGC 2070, is
Canopus in Carina is in the in the southeast, but it is best seen
southeast, with Sirius (see p.264) in in January. In the north, the
Canis Major rising in the east. galaxies M31 and M33 are visible,
Overhead is Cetus, containing the while the Pleiades (see p.287) and
long-period variable star Mira. Hyades clusters (see p.286) are
moving higher in the east.

uranus neptune
PISCES AQUARIUS
12 11 10 09 08 07 06 05
12
11 CAPRICORNUS
10
09
08
07
06
05

CETUS AQUARIUS

9pm classic variable
The long-period variable star Mira
PLEIADES ARIES (centre) appears strongly red when noon
near maximum brightness. The
TAURUS 05 9th-magnitude star to its left is
11 unrelated.
ES 6pm

3pm

PISCES 10°
0°
Mira 10 AQUARIUS Altair OPHIUCHUS -10°

09 CAPRICORNUS
Fomalhaut
08 08 12 07 11 10 06 -20° the night sky
05 11 05 08 06 -30°
evening -40°
SAGITTARIUS Antares -50°

Shaula

sky SCORPIUS

OBSERVATION TIMES

Date Standard Daylight-
time saving time

LOOKING NORTH 15 October Midnight 1am
1 November 11pm Midnight
NOVEMBER | NORTHERN LATITUDES 15 November 10pm 11pm
1 December 9pm 10pm
15 December 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N Zeniths
Variable Galaxy Globular Open Diffuse Planetary 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

Star Motion

North

LOOKING SOUTH

NOVEMBER | NORTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N Zeniths
Variable Galaxy Globular Open Diffuse Planetary 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

OBSERVATION TIMES

Date Standard Daylight-
time saving time

LOOKING NORTH 15 October Midnight 1am
1 November 11pm Midnight
NOVEMBER | SOUTHERN LATITUDES 15 November 10pm 11pm
1 December 9pm 10pm
15 December 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

Star Motion

North

LOOKING SOUTH

NOVEMBER | SOUTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

480 monthly sky guide

special events December

phases of the moon

full moon new moon The Sun reaches its farthest point south of the celestial equator this month, on
2006 5 December 21–22 December. As a result, northern hemisphere nights are the longest of the
2007 24 December 20 December year, while in the southern hemisphere they are the shortest.The Earth has now
2008 12 December 9 December completed another annual circuit of the Sun, and the evening stars end the year as
2009 2, 31 December 27 December they began, with the tableau of Orion and Taurus returning to centre stage.
2010 21 December 16 December
2011 10 December 5 December
2012 28 December 24 December
13 December

planets Northern latitudes

2005: 12 December Mercury is at greatest THE STARS DEEP-SKY OBJECTS grouping which outlines the Bull’s
morning elongation, magnitude -0.2. face. In addition to these
2006: 10 December Mercury and Overhead lies Perseus, containing Large, bright clusters of stars groupings, the Double Cluster in
Jupiter 0.2° apart in the eastern dawn sky. the famous variable star Algol (see abound in the December evening Perseus, NGC 869 and NGC 884,
2006: 10 December Mercury and Mars p.272). From Perseus, the Milky sky. In central Perseus, a few already encountered in November,
are 1° apart in the eastern dawn sky. Way leads northwestwards to dozen stars cluster around the remains well placed.
2006: 11–12 December Mars and Cassiopeia and Cygnus, which is constellation’s brightest member,
Jupiter 0.8° apart in the eastern dawn sky. out of sight for those at around Alpha (α) Persei or Mirphak.They METEOR SHOWER
2007: 24 December Mars is at 20°N or closer to the equator. In form a group known as the Alpha
opposition, magnitude -1.6. the other direction, the Milky Way Persei cluster, which covers several The year’s second-best meteor
2008: 1 December Venus and Jupiter extends southeastwards via Auriga diameters of the full Moon and is shower, the Geminids, reaches a
are 2° apart in the western evening sky, and past Taurus to Gemini and a fine sight through binoculars. peak around 13–14 December,
next to a crescent Moon. the northern arm of Orion.The when up to one meteor per
2009: 18 December Mercury is at Square of Pegasus is in the west, In Taurus lies probably the minute can be seen radiating from
greatest evening elongation, magnitude -0.3. while the Winter Triangle of finest open cluster in the entire a point near Castor in Gemini.
2010: 1 December Mercury is at greatest Betelgeuse (see p.252) in Orion, sky, the Pleiades or M45 (see Lesser activity is seen for a few
evening elongation, magnitude -0.4. Procyon (see p.280) in Canis p.287). At least six members are days before the peak, but numbers
2011: 23 December Mercury is at greatest Minor, and Sirius (see p.264) in visible to normal eyesight, but fall off rapidly afterwards.
morning elongation, magnitude -0.3. Canis Major dominates the binoculars bring dozens more into
2012: 3 December Jupiter is at southeast. By comparison with the view.Taurus contains an even Midnight
opposition, magnitude -2.8. richness of this southeastern part larger cluster, the Hyades (see 3am
2012: 4 December Mercury is at greatest of the sky, the southwest seems p.286), a
morning elongation, magnitude -0.3. dull and empty, as it is occupied V-shaped
by the faint constellations Aries,
eclipses Pisces, and Cetus. As the 6am Capella
year ends, Sirius lies due
2009: 31 December A partial eclipse of south around Castor TA
the Moon is visible from Australia, Asia, midnight.
Africa, and Europe. Pollux Aldebaran
2010: 21 December A total eclipse of 9AM HYA
the Moon is visible from North and South GEMINI
America, and the Pacific Ocean. Bellatrix
2011: 10 December A total eclipse of
the Moon is visible from the Pacific Ocean, Rigel
Australasia, and Asia.

07

noon Arcturus LEO 09 05
10° 06
Regulus

11 07 CANCER Betelgeuse
08

0° 09 Procyon

OPHIUCHUS VIRGO 10

-10° 06 05 12 07 10 11
-20° 11 12 12 Spica
-30°
06 LIBRA 05

the night sky 08 09 sky

Antares

o r n ing

-40° SCORPIUS m the Geminids
The Geminid meteors streak
-50° across the sky in mid-
December. In this picture, the
bright star at centre left is
Sirius and the southern part

of Orion is at top right.

december 481

Southern latitudes

THE STARS Major form a large triangle, which
is a sign of the approaching
The distinctive figures of Orion southern summer.
and Taurus are high in the
northeast, with Gemini and Auriga DEEP-SKY OBJECTS
closer to the horizon. Perseus lies
low in the north, while the Square December and January evenings
of Pegasus sets in the northwest, are the best time for southern
followed by Pisces. Fomalhaut observers to see the Pleiades (see
(see p.249) in Piscis Austrinus is p.287) and Hyades (see p.286),
in the southwest. two large and prominent open star
clusters north of the equator in
Eridanus, the River, meanders Taurus.The Large Magellanic
southwestwards from the foot of Cloud, containing the Tarantula
Orion, ending at the bright star Nebula, NGC 2070, is high in the
Achernar. Brighter Canopus is southeast but it is better seen in
high in the southeast in Carina. January. Overall, the southern
The Large and Small Magellanic evening sky is bereft of prominent
Clouds (see p.300 and p.301) lie deep-sky objects near the celestial
high in the south, either side of meridian this month.
the celestial meridian. In the east,
Betelgeuse in Orion, Procyon in
Canis Minor, and Sirius in Canis
the night skythe large magellanic cloud
POSITIONS OF THE PLANETS The LMC (bottom) lies deep in the southern
09 09 09 09 09 09 09 09 sky between the bright stars Canopus (left)
09 09 09 09 09 09 09 09This chart shows the positions of the planets in December from 2005 to 2012. The planets areand Achernar (top right). The small pink
represented by coloured dots, while the number inside each dot denotes the year. For all planets patch on the LMC is the Tarantula Nebula.
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09apart from Mercury, the dot indicates the planet’s position on 15 December. Mercury is shown only
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09when it is at greatest elongation (see p.64) – for the specific date, refer to the table, left.uranus
PISCES
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09MercuryMarsSaturnNeptune neptune
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09Venus09 Ju0p9iter 090U9ranus 09 AQUARIUS
09 09 09 12 11 10 09 08 07 06 05
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09examples
09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 CAPRICORNUS
09 09 09 09 Sat0u9rn’s po0si9tion on09 09 09 09 Ma0r9s’s pos0it9ion on 0159 Decem09ber 200099. The arrow 12
15 December 2009 indicates the planet is in retrograde motion (see p.64). 11
10
09 09 09 09 09 09 09 09
08
07
CETUS 06 05

Capella AQUARIUS

6pm

07 TAURUS PLEIADES ARIES 3pm
elgeuse
12 05 PISCES noon
11 10°
Aldebaran
HYADES Altair 0°

Bellatrix

AQUARIUS

Mira 10

Rigel CAPRICORNUS -10°

09 08 05 08 10 -20°
Fomalhaut 11 07
12 09
06 10

evening -30°

SAGITTARIUS Shaula

-40°

sky -50°

OBSERVATION TIMES

Date Standard Daylight-
time saving time

LOOKING NORTH 15 November Midnight 1am
1 December 11pm Midnight
DECEMBER | NORTHERN LATITUDES 15 December 10pm 11pm
1 January 9pm 10pm
15 January 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N Zeniths
Variable Galaxy Globular Open Diffuse Planetary 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

Star Motion

North

LOOKING SOUTH

DECEMBER | NORTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5 Horizons 60°N 40°N 20°N Zeniths
Variable Galaxy Globular Open Diffuse Planetary 60°N 40°N 20°N Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

OBSERVATION TIMES

Date Standard Daylight-
time saving time

LOOKING NORTH 15 November Midnight 1am
1 December 11pm Midnight
DECEMBER | SOUTHERN LATITUDES 15 December 10pm 11pm
1 January 9pm 10pm
15 January 8pm 9pm

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

Star Motion

North

LOOKING SOUTH

DECEMBER | SOUTHERN LATITUDES

South

STAR MAGNITUDES DEEP-SKY OBJECTS POINTS OF REFERENCE
-1 0 1 2 3 4 5
Variable Galaxy Globular Open Diffuse Planetary Horizons 0° 20°S 40°S Zeniths 0° 20°S 40°S Ecliptic
star cluster cluster nebula nebula

THE NIGHT SKY

glossary

GLOSSARY

GGGLUUOIIS SDDEEA RTTYOO TT HH EE UU NN II VV EE RRSS EE A antiparticle An elementary particle An atom has the same number of light, but whose binary nature is
that has the same mass as a particle of orbiting electrons as it has protons, so revealed by its spectrum.The
absolute magnitude see magnitude. ordinary matter but exactly opposite it is neutral (has no electrical charge). combined spectrum of the two stars
values of other quantities such as spin The chemical identity of an atom is contains two sets of spectral lines that
absorption line see spectral line. and electrical charge. For example, the determined by the number of shift in wavelength as the stars revolve
antiparticle of the negatively charged protons in its nucleus (its atomic round each other. An eclipsing binary
absorption nebula see nebula. electron is the positively charged number). An atom of hydrogen (the is a system in which each star
positron. If a particle and its antiparticle simplest and lightest element) alternately passes in front of the other,
accelerating universe A universe that collide, both are annihilated and consists of a single proton and a cutting off all or part of its light and
expands at an accelerating rate. converted into energy. single electron. See also electron, causing a periodic variation in the
Current evidence indicates that the neutron, proton. combined light of the two stars. See
expansion of our Universe had been aperture The clear diameter of the also Doppler effect, spectral line.
slowing down under the action of objective lens or primary mirror of a aurora A glowing, fluctuating display of
gravity until about 6 billion years telescope or other optical instrument. light that is produced when charged black body An idealized body that
ago, but that since then it has been particles entering a planet’s upper absorbs and re-emits all the radiation
accelerating.The acceleration is aphelion The point on its elliptical atmosphere, usually in the vicinity of that falls on its surface and which is a
believed to be driven by the repulsive orbit at which a body such as a its north and south magnetic poles, perfect radiator. A black body emits a
influence of dark energy. See also planet, asteroid, or comet is at its collide with atoms and stimulate continuous spectrum of radiation
dark energy. greatest distance from the Sun. them to emit light. (black-body radiation) that peaks in
brightness at a wavelength that
accretion (1) The colliding and apogee The point on its elliptical orbit autumnal equinox see equinox. depends on its surface temperature –
sticking together of small, solid around the Earth at which a body the higher the temperature, the
particles and bodies to make such as the Moon or a spacecraft is at azimuth The angle between the north shorter the wavelength of peak
progressively larger ones. (2) The its greatest distance from the Earth. point on an observer’s horizon and brightness. See also spectrum.
process whereby a body grows in See also perigee. a celestial object, measured in a
mass by accumulating matter from clockwise direction around the black-dwarf star A white-dwarf star
its surroundings. An accretion disc is apparent magnitude see magnitude. horizon.The azimuth of due north is that has cooled to such a low
a disc of gas that revolves around a 0°, due east 90°, due south 180°, and temperature that it emits no
star or a compact object such as a arachnoid A type of structure, found due west 270°. See also altitude. detectable light.There has not been
white dwarf, neutron star, or black on the surface of Venus, that consists enough time since the origin of the
hole and which has been drawn in of concentric circular or oval fractures B Universe for any star to cool down
from a companion star or from or ridges, together with a complex enough to become a black dwarf. See
neighbouring gas clouds. network of fractures or ridges that background radiation see cosmic also brown-dwarf star, white-dwarf star.
radiate outwards. Its name derives microwave background radiation.
active galaxy A galaxy that emits an from its superficial resemblance to a black hole A compact region of space,
exceptional amount of energy over spider’s web.Typical diameters range barred spiral galaxy A galaxy that has surrounding a collapsed mass, within
a wide range of wavelengths, from from 50 to 175km (30–110 miles). spiral arms emanating from the ends which gravity is so powerful that no
radio waves to X-rays. An active of an elongated, bar-shaped, nucleus. material object, light, or any other
galactic nucleus (AGN) is the compact, asterism A conspicuous pattern of See also galaxy, spiral galaxy. kind of radiation can escape to the
highly luminous core of an active stars that is not itself a constellation. outside Universe.The radius of a
galaxy that, in many cases, varies A well-known example is the Plough, baryon A particle, composed of three black hole is called the Schwarzschild
markedly in brightness over time, and or Big Dipper, which forms part of quarks, that is acted on by the strong radius, and its boundary is known as
is thought to be powered by the the constellation Ursa Major (the nuclear force. Examples include the event horizon.The greater its mass,
accretion of gas onto a supermassive Great Bear). See also constellation. protons and neutrons, the building the larger its radius.When a body
black hole. See also black hole, galaxy. blocks of atomic nuclei. collapses to form a black hole, all of
asteroid One of the vast number its mass becomes compressed into a
active prominence see prominence. of small bodies that revolve Big Bang The event in which the central point, a point of infinite
independently around the Sun.Their Universe was born. According to Big density called a singularity. A stellar-
albedo The ratio of the amount of diameters range from a few metres Bang theory, the Universe originated mass black hole forms when the core
light reflected by a body, such as a (yards) to around 1,000km (600 miles). a finite time ago in an extremely hot, of a high-mass star collapses; its mass
planet or a part of a planet’s surface, While the greatest concentration of dense initial state and ever since then is likely to be in the region of 3–100
to the amount of light that it receives asteroids is in the Main Belt, which lies has been expanding.The Big Bang was times the mass of the Sun. A super-
from the Sun. Albedo values range between the orbits of Mars and the origin of space, time, and matter. massive black hole, with a mass in the
from 0, for a perfectly dark object Jupiter, asteroids are found region of a few million to a few
that reflects nothing, to 1, for a throughout the Solar System. A near- Big Crunch The final state that will billion solar masses, is an object that
perfect reflector. Earth asteroid (NEA) is a body whose be reached by the Universe if it forms when a very large mass
orbit comes close to, or intersects, the eventually ceases to expand and then collapses, or a number of black holes
altazimuth mounting A mounting orbit of the Earth. Formally, a near- collapses in on itself. merge into one, in the core of a
that enables a telescope to be rotated Earth asteroid is defined as one that galaxy. See also active galaxy, singularity.
in altitude (around a horizontal axis) has a perihelion distance of less than Big Rip The tearing apart of all forms
and in azimuth (around a vertical 1.3 times the Earth’s mean distance of structure in the Universe – galaxy blazar The most variable type of active
axis). Many large modern telescopes from the Sun. See also Kuiper Belt. clusters, galaxies, stars, planets, atoms, galaxy, which includes BL Lacertae
are mounted in this way, using and elementary particles – that is objects and the most violently
computer-controlled motors to astronomical unit (AU) A unit of expected to occur should the variable quasars. See also active galaxy,
drive the telescope in altitude and distance measurement equal to the repulsive effect of dark energy BL Lacertae object, quasar.
azimuth so as to track the motion semimajor axis of the Earth’s elliptical become infinitely strong in a finite
of an object across the sky. See also orbit, equivalent to the average of the time. See also dark energy. BL lacertae object A type of active
altitude, azimuth, equatorial mounting. maximum and minimum distances galaxy that has no detectable
between the Earth and Sun. 1 AU = binary star Two stars that revolve absorption or emission lines in its
altitude The angular distance between 149,598,000km (92,956,000 miles). around each other under the influence spectrum but which is believed to be
the horizon and a celestial body. of their mutual gravitational attraction. similar to a quasar.The name derives
Altitude takes values from 0° (for an atom A basic building block of matter Each member star orbits the centre of from an object in the constellation
object on the horizon) to 90° (for that is the smallest unit of a chemical mass of the system, a point that lies Lacerta that was at first thought to be
an object that is directly overhead). element possessing the characteristics closer to the more massive of the two a variable star. See also quasar.
See also azimuth. of that element. It consists of a stars. A spectroscopic binary is a system
nucleus of protons and neutrons, in which the two stars are too close
antimatter Material composed of surrounded by a cloud of electrons. to be resolved into separate points of
antiparticles. See antiparticle.

glossary

blue shift The displacement of spectral surface of this sphere. See also celestial A universe will be closed if its coronal mass ejection A huge, rapidly G U I DE TO T H E UGNLIOVSESRASREY
lines to shorter wavelengths that equator, celestial poles. average density exceeds a particular expanding bubble of plasma that is
occurs when a light source is value called the critical density. In the ejected from the Sun’s corona.
approaching an observer. See also centre of mass The point within an absence of a repulsive force, a closed Containing billions of tons of
Doppler effect, red shift, spectral line. isolated system of bodies around universe will eventually cease to material in the form of ions and
which those bodies revolve.Where expand and will then collapse. See electrons, together with associated
Bok globule A compact dark nebula, the system consists of two bodies (for also flat universe, open universe, magnetic fields, a typical coronal mass
roughly spherical in shape, which example, a binary star), it is located at oscillating universe. ejection propagates outwards through
contains 1 to 1000 solar masses of gas a point on a line joining their interplanetary space at a speed of
and dust and has a diameter of centres. If both bodies have the same coma The cloud of gas and dust that several hundred kilometres (miles) per
between 0.1 and a few light-years. mass, the centre of mass lies midway surrounds the nucleus of a comet and second. See also corona, ion, plasma.
Globules of this kind are believed to between them, whereas if one body which comprises its glowing “head”.
be cool concentrations of gas and is more massive than the other, it lies See also comet. cosmic microwave background
dust that eventually will collapse to closer to the more massive of the two. radiation (CMBR) Remnant
form protostars.They are named after comet A small body composed mainly radiation from the Big Bang, which is
Dutch-born astronomer Bart Bok, Cepheid variable A type of variable of dust-laden ice that revolves around detectable as a faint distribution of
who made a detailed study of these star that increases and decreases in the Sun, usually in a highly elongated microwave radiation across the whole
objects. See also protostar. brightness in a regular, periodic way. orbit. Each time it approaches the sky. See also Big Bang.
Cepheids are pulsating variables, which Sun, gas and dust evaporate from its
brown-dwarf star A body that forms vary in brightness as they expand and nucleus (the solid core of the comet) cosmic rays Highly energetic
out of a contracting cloud of gas in contract.The more luminous the to form an extensive cloud, called the subatomic particles, such as electrons,
the same way as a star, but which, Cepheid, the longer its period of coma, and one or more tails. See also protons, and atomic nuclei, that
because it contains too little mass, variation. See also variable star. coma, tail. hurtle through space at speeds close
never becomes hot enough to ignite to the speed of light.
the nuclear-fusion reactions that power Chandrasekhar limit The maximum conjunction A close alignment in the
a normal star.With less than 8 per cent possible mass for a white-dwarf star. sky of two celestial bodies, which cosmological constant An extra term
of the Sun’s mass, a brown dwarf If the mass of a white dwarf exceeds occurs when both bodies lie in the in Einstein’s relativity equations
glows dimly at infrared wavelengths, this limit, which is about 1.4 solar same direction as viewed from the which, if it has a positive value,
fading gradually as it cools down. masses, gravity will overwhelm its Earth.When a planet lies directly on corresponds to a repulsive force that
internal pressure and it will collapse. the opposite side of the Sun from the could cause the Universe to expand
C The limit was first calculated by Earth, it is said to be at superior at an accelerating rate. Modern
Indian astrophysicist Subrahmanyan conjunction. If a planet passes between cosmologists associate the constant
caldera A bowl-shaped depression Chandrasekhar in 1931. See also the Earth and the Sun (Mercury and with a quantity called vacuum energy
caused by the collapse of a volcanic white-dwarf star. Venus are the only planets that can (residual energy that, according to
structure into an emptied magma do this), it is said to be at inferior quantum theory, exists even in a
chamber. A caldera is usually found at charge-coupled device (CCD) An conjunction. See also opposition. vacuum), one of the possible forms of
the summit of shield volcanoes such electronic imaging device that the dark energy believed to permeate
as those on Venus and Mars. consists of a large array of tiny light- constellation One of 88 regions of the the Universe. See also dark energy.
sensitive elements.The image of an celestial sphere. Each constellation
captured rotation See synchronous object is constructed by reading off contains a grouping of stars joined by cosmological red shift see red shift.
rotation. the electrical charges that accumulate imaginary lines to represent a figure.
in each element during an exposure. The constellations are officially cosmology The study of the nature,
carbonaceous chondrite see chondrite. referred to by the Latin names of structure, origin, and evolution of
chondrite A stony meteorite that these figures. Many have been named the Universe.
Cassegrain telescope A type of contains a large number of small, after mythological characters or
reflecting telescope in which the spherical objects called chondrules. A creatures (such as Orion, the Hunter) crater A bowl- or saucer-shaped
converging cone of light reflected carbonaceous chondrite is one that is but some after more mundane depression in the surface of a
from a concave primary mirror is rich in carbon, carbon compounds, objects (for example, Sextans, the planet or satellite, or at the summit of
then reflected back from a convex and volatile materials. Carbonaceous Sextant). See also asterism. a volcano. Many have raised walls and
secondary mirror, through a hole in chondrites are thought to be some of some have a central peak. An impact
the primary mirror, to a focus at the the least-altered primitive remnants continuous spectrum see spectrum. crater is one excavated by an
rear of the instrument.The design of the protoplanetary disc from meteorite, asteroid, or comet impact,
was devised by Guillaume Cassegrain which the Solar System formed. See convection The transport of heat by whereas a volcanic crater is the cavity
in 1672. See also reflecting telescope, also meteorite, protoplanetary disc. rising bubbles or plumes of hot liquid from which a volcano discharges
Schmidt–Cassegrain telescope. or gas. In a convection cell, rising material. Raised walls are created by
chromosphere The thin layer in the streams of hot material cool, accumulation of ejected material.
cataclysmic variable see variable star. Sun’s atmosphere that lies between spread out, and then sink down
the photosphere (the visible surface) to be reheated, so maintaining a critical density see flat universe.
celestial equator A great circle on the and the corona. Its faint, reddish-pink continuous circulation.
celestial sphere that is a projection of light can be seen directly during a crust The thin, rocky, outermost layer
Earth’s own equator onto the total eclipse of the Sun when the core (1) The dense central region of a of a planet or major planetary
celestial sphere. See also celestial Moon hides the dazzling planet. (2) The central region of a satellite, which, like the Earth, has
sphere, great circle. photosphere. See also photosphere. star within which energy is generated separated into several layers, with the
by means of nuclear-fusion reactions. densest material towards its centre
celestial poles The two points at circumpolar A term used to describe a (3) A dense concentration of material and the least dense at its surface.
which the line of the Earth’s axis, star, or other celestial body, that within a gas cloud.
extended outwards, meets the remains above the horizon at all D
celestial sphere and around which times when viewed from a particular Coriolis effect The tendency of a wind
the stars appear to revolve.The place on the Earth’s surface. or current to be deflected from its dark energy A little-understood
north celestial pole lies directly initial direction as a consequence of a form of energy that appears to
above the Earth’s North Pole and the circumstellar disc A flattened, disc- planet’s rotation. In the case of the comprise about 70 per cent of the
south celestial pole directly above shaped cloud of gas and dust that Earth, the deflection is to the right in total amount of mass and energy in
the Earth’s South Pole. See also surrounds a star. A disc of this kind is the northern hemisphere and to the the Universe. It exerts a repulsive
celestial sphere. usually associated with a young or left in the southern hemisphere. effect and is believed to be causing
newly forming star, in which case it the expansion of the Universe to
celestial sphere An imaginary sphere, is composed of material from the corona The outermost region of the accelerate. See also accelerating universe.
that surrounds the Earth. As the original dusty gas cloud that atmosphere of the Sun or a star.The
Earth rotates from west to east, the collapsed to form the central star. See solar corona has an extremely low dark matter Matter that exerts a
sphere appears to rotate from east also protoplanetary disc. density and a very high temperature gravitational influence on its
to west. In order to define the (1–5 million degrees Celsius/about surroundings but does not emit
positions of stars and other celestial closed universe A universe that is 2–9 million degrees Fahrenheit). It detectable amounts of radiation. Dark
bodies, it is convenient to think of curved in such a way that space is cannot be observed except during a matter appears to make up a large
them as being attached to the inside finite but has no discernable boundary total eclipse of the Sun. See also fraction of the total amount of mass
(analogous to the surface of a sphere). eclipse, solar wind.

glossary

GLOSSARY contained in galaxies, galaxy clusters, of the Moon is in the shadow. lies inside the orbit of the Earth. See In such a universe, space is flat in the
and the Universe as a whole. During a total solar eclipse, the Sun also conjunction, opposition. sense that, apart from localized
is completely obscured by the dark distortions caused by massive bodies,
dark-matter halo see halo. disc of the Moon. A partial solar emission line see spectral line. its large-scale geometry is Euclidean
eclipse occurs when only part of the and light rays travel in straight lines.
dark nebula see nebula. Sun’s surface is hidden. If the Moon emission nebula see nebula. A universe will be flat if its overall
passes directly between the Sun and average density is equal to a particular
declination The angular distance of a the Earth when it is close to apogee, equatorial mounting A mounting that value, called the critical density. See
celestial body north or south of the it will appear smaller than the Sun, enables a telescope to be turned also closed universe, open universe,
celestial equator. Declination is and its dark disc will be surrounded around two axes, one of which (the oscillating universe.
positive (+) if the object is north of by a ring, or annulus, of sunlight; an polar axis) is parallel to, and the other
the celestial equator and negative (-) event of this kind is called an (the declination axis) perpendicular to, focal length The distance between the
if it is south of the celestial equator. annular eclipse. See also apogee. the Earth’s axis of rotation.The centre of a lens, or the front surface
A star on the celestial equator has a telescope can follow the motion of a of a concave mirror, and the point at
declination of 0°, whereas a star at eclipsing binary see binary star. celestial object across the sky by which it forms a sharp image of a
one of the celestial poles has a being driven round the polar axis in very distant object.
declination of 90°. See also celestial ecliptic The track along which the Sun the opposite direction to the Earth’s
equator, celestial sphere, right ascension. appears to travel around the celestial rotation at a rate of one revolution frequency The number of wave crests
sphere, relative to the background stars, per sidereal day. See also declination, of a wave motion that pass a given
declination axis see equatorial mounting. in the course of a year. It is equivalent right ascension, sidereal time. point in one second. In the case of an
to the plane of the Earth’s orbit. electromagnetic wave (for example,
diffuse nebula A luminous cloud of equinox An occasion when the Sun light) the frequency is equal to
gas and dust.The term “diffuse” refers ejecta Material thrown outwards by is vertically overhead at a planet’s the speed of light divided by the
to the cloud’s fuzzy appearance and the blast of an impact. Ejecta, which equator, and day and night have equal wavelength. See also electromagnetic
to the fact that it cannot be resolved is produced when a meteorite strikes duration for the whole planet. In the radiation.
into individual stars. See also nebula. the surface of a planet or moon and case of the Earth, the northern vernal
excavates a crater, consists of freshly equinox is the point at which the Sun fusion (nuclear fusion) The process
direct motion see retrograde motion. exposed material that may be crosses the celestial equator from south whereby atomic nuclei are joined
markedly brighter than the adjacent to north, on or around 21 March each together during energetic collisions
direct rotation see retrograde rotation. surface. Sometimes the ejected year, and the northern autumnal equinox to form heavier atomic nuclei, with
material forms extensive streaks, or is the point at which the Sun crosses an associated release of large amounts
Doppler effect The observed change in rays, which radiate from the point of the celestial equator from north to of energy. Stars are powered by fusion
the wavelength or frequency of impact. An ejecta blanket is a south, on or around 22 September. reactions that take place in their
radiation that is caused by the motion continuous sheet of deposited ejecta See also right ascension. central cores. In a main-sequence star
of its source towards or away from an that surrounds a crater. See also crater. such as the Sun, fusion reactions
observer. See also blue shift, red shift. eruptive prominence see prominence. convert hydrogen into helium. See
electromagnetic (EM) radiation also main sequence.
double star Two stars that appear close Oscillating electric and magnetic eruptive variable see variable star.
together in the sky. If the two stars disturbances that propagate energy G
revolve around each other, the system through space in the form of waves escape velocity The minimum speed
is called a binary. An optical double star (electromagnetic waves). Examples at which a projectile must be galactic cluster see open cluster.
consists of two stars that appear to be include light and radio waves. launched in order to recede forever
close together only because they from a massive body and not fall galaxy A large aggregation of stars
happen to lie in almost exactly the electromagnetic spectrum The back.The escape velocity at the and clouds of gas and dust. Galaxies,
same direction when viewed from complete range of electromagnetic Earth’s surface is 40,320kph which may be elliptical, spiral, or
the Earth; they lie at different radiation from the shortest (25,200mph). irregular in shape, contain from a
distances and are not physically wavelengths (gamma rays) to the few million to several trillion stars
connected. See also binary star. longest wavelengths (radio waves). event horizon see black hole. and have diameters ranging from a
few thousand to over a hundred
dwarf planet A celestial body that electron A lightweight fundamental extrasolar planet (exoplanet) A thousand light-years.The Sun is a
orbits the Sun and has sufficient mass particle with negative electrical planet that revolves around a star member of the Milky Way galaxy,
and gravity to be spherical, but has not charge. A cloud of electrons other than the Sun. which is also sometimes known as
cleared the region around its orbit of surrounds the nucleus of an atom. the Galaxy. See also Milky Way.
other bodies, and is not a satellite. The number of orbiting electrons F
in an atom is the same as the number galaxy cluster An aggregation of
dwarf star An alternative name for of protons in its nucleus. facula (plural: faculae) A patch of galaxies held together by gravity.
a main-sequence star that was enhanced brightness on the solar Clusters that contain up to a few
originally devised to distinguish ellipse An oval curve drawn around photosphere that may be seen in a tens of member galaxies are called
main-sequence stars, such as the Sun, two points called foci (singular: focus) white-light image of the Sun, usually groups. Larger clusters are divided
from the much more luminous giant such that the total distance from one near the edge of the Sun’s visible disc into regular and irregular clusters,
stars on the Hertzsprung–Russell focus to any point on the curve and where the background brightness is depending on their degree of
diagram. See also Hertzsprung–Russell then back to the other focus is lower. Faculae correspond to regions structure.The most richly
diagram, main sequence. constant.The maximum diameter of that are hotter than their immediate populated regular clusters (rich
an ellipse is the major axis, and half of surroundings.They are associated clusters) contain up to several
E this diameter is the semimajor axis. with active solar regions but may thousand galaxies.
The two foci lie on the major axis; appear before, and persist after, any
eccentricity (e) A measure of how the greater their separation, the more sunspots that develop in those galaxy supercluster A cluster of
much an ellipse deviates from a elongated the ellipse. See also regions. See also photosphere, sunspot. galaxy clusters, which is a loose
perfect circle. Eccentricity takes a eccentricity, orbit. aggregation of up to about ten
value between 0 and 1; a circle has Fraunhofer line One of the 574 dark thousand galaxies, spread through a
eccentricity of 0, and the most elliptical galaxy A galaxy that appears absorption lines in the spectrum of volume of space with a diameter of
elongated ellipses approach an round or elliptical in shape and the Sun that were identified by the up to about 200 million light-years.
eccentricity of 1. See also ellipse. normally contains very little gas 19th-century German optician and See also galaxy cluster.
or dust. See also galaxy. instrument maker Joseph von
eclipse The passage of one celestial Fraunhofer. See also spectral line. Galilean moon One of the four
body into the shadow cast by elongation The angle between the Sun largest natural satellites of the planet
another. A lunar eclipse occurs when and a planet, or other Solar System flare star A faint, cool, red-dwarf star Jupiter, which were discovered in
the Moon passes into the Earth’s body, when viewed from the Earth. that displays sudden, short-lived 1610 by the Italian astronomer
shadow and a solar eclipse when part The elongation of a planet is 0° increases in luminosity caused by Galileo Galilei. In order of distance
of the Earth’s surface enters the when it is in conjunction with the extremely powerful flares that occur from the planet, they are Io, Europa,
shadow cast by the Moon. A total Sun and 180° when it is at above its surface. See also red-dwarf Ganymede, and Callisto.
lunar eclipse takes place when the opposition. Greatest elongation is the star, solar flare.
whole of the Moon lies within the maximum possible elongation of a
dark cone of the Earth’s shadow, and body, such as Mercury or Venus, that flat universe A universe in which the
a partial lunar eclipse when only part overall net curvature of space is zero.

glossary

gamma radiation Electromagnetic gravity The attractive force that acts oxygen. Helium burning takes place the dominant form of radiation G U I DE TO T H E UGNLIOVSESRASREY
radiation with extremely short between material bodies, particles, in the core of a star that has left the emitted from many cool astronomical
wavelengths (shorter than X-rays) and photons. According to the theory main sequence and become a red objects, such as interstellar dust
and very high frequencies. Gamma of gravity developed in the 17th giant, and it may occur again, later clouds. See also electromagnetic radiation.
radiation occupies the shortest- century by Isaac Newton (Newtonian in a star’s evolution, in a shell
wavelength region of the spectrum. gravitation), the force of gravity acting surrounding the core. See also fusion, interstellar medium The gas and dust
See also electromagnetic radiation, between two bodies is proportional main sequence, red-giant star. that permeates the space between the
electromagnetic spectrum. to the product of their masses divided stars within a galaxy.
by the square of the distance between Hertzsprung–Russell (HR) diagram A
gamma-ray burst (GRB) A sudden their centres. For example, if the diagram on which stars are plotted as ion A particle or system of particles
burst of gamma radiation from a distance between the bodies is points according to their luminosity with a net electrical charge. Positive
source in a distant galaxy. Gamma-ray doubled, the force of attraction is and surface temperature. Luminosity ions are commonly formed when an
bursts are the most powerful reduced to one quarter of its previous (or absolute magnitude) is plotted atom loses one or more of its
explosive events in the present-day value. See also relativity. on the vertical axis, and surface electrons, whereas negative ions result
Universe.They may be triggered by temperature (or spectral class or from an excess of electrons. Ions may
collisions between neutron stars or great circle A circle on the surface of colour) is plotted on the horizontal form from complexes of former
black holes or by an extreme version a sphere, the plane of which passes axis. Astrophysicists use the atoms.The process by which an atom
of a supernova called a hypernova. through the centre of the sphere and Hertzsprung–Russell diagram to or complex gains or loses an electron
which exactly divides the sphere into classify stars. Depending on a star’s to become charged is called
gas planet (gas giant) A large planet two equal hemispheres. Its name position on the diagram, it may be ionization. See also electron, photon.
that, like Jupiter or Saturn, consists derives from the fact that it is the classified as, for example, a main-
predominantly of hydrogen and largest circle that can be drawn on sequence star, a giant, or a dwarf. irregular cluster see galaxy cluster.
helium. Beneath its thick gaseous the surface of a sphere. See also
atmosphere, the pressure is so great celestial equator, meridian. Hubble constant see Hubble’s law. irregular galaxy A galaxy that has no
that hydrogen and helium exist in well-defined structure or symmetry.
liquid form. See also rocky planet. greenhouse effect The process by Hubble’s law The observed
which atmospheric gases make the relationship between the red shifts in isotope Any one of two or more forms
gegenschein A very faint patch of surface of a planet hotter than would the spectra of remote galaxies and of a particular chemical element, the
light that sometimes may be seen on be the case if the planet had no their distances, which implies that the atoms of which contain the same
a clear, moonless night in the region atmosphere. Incoming sunlight is speeds at which galaxies are receding number of protons but different
of sky directly opposite the position absorbed at the surface of a planet are directly proportional to their numbers of neutrons. For example,
of the Sun. It is caused by sunlight and re-radiated as infrared radiation, distances.The Hubble constant (or helium-3 and helium-4 are isotopes
that has been reflected back towards which is then absorbed by greenhouse Hubble parameter) – denoted by the of helium; a nucleus of helium-4 (the
the Earth by interplanetary dust gases such as carbon dioxide, water symbol H0 – is the constant of heavier, and more common, isotope)
particles lying beyond the orbit vapour, and methane. Part of this proportionality that relates speed of contains two protons and two
of the Earth. See also zodiacal light. trapped radiation is re-radiated back recession to distance. neutrons, whereas a nucleus of
down towards the ground, so raising helium-3 contains two protons and
general theory of relativity see its temperature. hydrogen burning The generation of one neutron. See also atom, nucleus.
relativity. energy by means of fusion reactions
H that convert hydrogen into helium. K
geocentric (1) Treated as being viewed Hydrogen burning takes place in the
from the centre of the Earth. (2) HII region A glowing region of ionized core of a main-sequence star.When a Kepler’s laws of planetary motion
Having the Earth at the centre (of a hydrogen surrounding one or more star has consumed all the available Three laws, devised in the early 17th
system). Geocentric coordinates are a hot, highly luminous stars. An HII hydrogen in its core, the core century by Johannes Kepler, that
system of positional measurements region is often just a part of a more contracts and hydrogen burning then describe the orbital motion of planets
(such as right ascension and extensive cloud of gas and dust, the continues in a thin shell surrounding around the Sun. In essence, the first
declination) that are treated as being remainder of which has not been the core. See also fusion, main sequence, law states that each planet’s orbit is an
measured from the centre of the ionized and is not shining. See also proton–proton reaction. ellipse, the second shows that a
Earth. A satellite that is travelling ion, nebula. planet’s speed varies as it travels
around the Earth is in a geocentric hypernova see gamma-ray burst. around its orbit, and the third links its
orbit. Geocentric cosmology was the halo A spherical region surrounding a orbital period (the time taken to
ancient theory that the Sun, Moon, galaxy that contains a distribution of I travel round the Sun) to its average
planets, and stars revolved around a globular clusters, thinly scattered stars, distance from the Sun.
central Earth. See also heliocentric. and some gas. A dark-matter halo is a impact crater see crater.
distribution of dark matter within Kuiper Belt (Edgeworth–Kuiper Belt)
giant star A star that is larger and much which a galaxy is embedded. inclination The angle at which one A flattened distribution of icy
more luminous than a main-sequence plane is tilted relative to another. planetesimals that orbit the Sun at
star of the same surface temperature. heliocentric (1) Treated as being The inclination of a planetary orbit distances in the region of 30–100
See also Hertzsprung–Russell diagram, viewed from the centre of the Sun. is the angle between its plane and the times the Earth’s distance from the
main sequence, red giant. (2) Having the Sun at the centre (of plane of the ecliptic (the plane of the Sun and which is the source of many
a system). Heliocentric coordinates Earth’s orbit).The inclination of a of the shorter-period comets. See
globular cluster A near-spherical specify the position of an object as planet’s equator is the angle between also Oort Cloud, planetesimal.
cluster of between 10,000 and more seen from the centre of the Sun. A the plane of its orbit and the plane of
than 1 million stars. Globular clusters, body that is revolving round the Sun its equator. See also ecliptic, orbit. L
which consist of very old stars, are follows a heliocentric orbit. Heliocentric
located predominantly in the halos of cosmology is a model of the Universe, inferior conjunction see conjunction. lenticular galaxy A galaxy that is
galaxies. See also open cluster. such as the one proposed in 1543 by shaped like a convex lens. It has a
Nicolaus Copernicus, in which the inferior planet A planet that travels central bulge that merges into a disc,
gravitation see gravity. planets revolve around a central Sun. round the Sun on an orbit that is but no spiral arms. See also galaxy,
inside the orbit of the Earth.The two spiral galaxy.
gravitational lens A massive body, or a heliosphere The region of space inferior planets are Mercury and
distribution of mass (such as a galaxy around the Sun within which the Venus. See also superior planet. lepton A fundamental particle, such as
cluster), whose gravitational field solar wind and interplanetary an electron or a neutrino, that is not
deflects light rays from a more distant magnetic field are confined by the inflation A sudden, short-lived episode acted on by the strong nuclear force.
background object, thereby acting as pressure of the interstellar medium. of accelerating expansion thought to
a lens to produce a magnified or Its boundary is called the heliopause. have occurred at a very early stage in light-year (ly) A unit of distance equal
distorted image, or images, of that See also interstellar medium, solar wind. the history of the Universe (about to the distance light travels in one
background object. 10-35 seconds after the beginning of year – 9,460 billion km (5,878
helium burning The generation of time). See also Big Bang. billion miles).
gravitational wave A wave-like energy by means of fusion reactions
distortion of space that propagates at that convert helium into carbon and infrared radiation Electromagnetic limb The edge of the observed disc of
the speed of light. Although waves of radiation with wavelengths longer the Sun, the Moon, or a planet.
this kind have not yet been detected than visible light but shorter than
directly, there is strong, indirect microwaves or radio waves. Infrared is
evidence that they exist.

glossary

GLOSSARY Local Group The small cluster of more were located at a standard distance of form meteoroid streams. See also electrical charge and which travels at
than 40 member galaxies to which 10 parsecs (32.6 light-years) from asteroid, comet, meteor, meteorite. very close to the speed of light.
the Milky Way galaxy belongs.The Earth. See also luminosity, parsec.
other major members are the spiral Milky Way (1) The spiral galaxy that neutron A particle, composed of three
galaxies M31 (the Andromeda Galaxy) Main Belt see asteroid. contains the Sun, sometimes also quarks, that has zero electrical charge
and M33. Most of the members are referred to as the Milky Way galaxy or and a mass fractionally greater than
small (or dwarf) elliptical or irregular main sequence A band that slopes the Galaxy. (2) A faint, misty band of that of a proton. Neutrons are found
galaxies. See also galaxy cluster. diagonally from the upper left (hot, light that stretches across the night in the nuclei of atoms. See also atom.
high-luminosity region) to the lower sky and consists of the combined
local sidereal time see sidereal time. right (cool, low-luminosity region) of light of vast numbers of stars and neutron star An exceedingly dense,
the Hertzsprung–Russell diagram and nebulae that lie in the disc and spiral compact star that is composed almost
luminosity The total amount of energy which contains about 90 per cent of arms of our galaxy. See also galaxy. entirely of tightly packed neutrons. A
emitted in one second by a source of stars. Main-sequence stars, such as the typical neutron star has a diameter of
radiation, such as the Sun or a star. Sun, shine by converting hydrogen in Mira variable A class of long-period around 10km (6 miles) yet has about
The luminosity of a star can be their cores to helium. See also dwarf variable star named after the star the same mass as the Sun. A neutron
expressed in watts or in units of star, Hertzsprung–Russell diagram. Mira – Omicron (ο) Ceti – in the star forms when the core of a high-
solar luminosity (the luminosity of constellation Cetus. Mira variables mass star collapses, triggering a
the Sun is 3.8 x 1026 watts). Stars major axis see ellipse. are cool, giant pulsating stars that supernova explosion. See also pulsar,
are divided into luminosity vary in brightness over periods supernova.
classes denoted by Roman numerals. mantle The rocky layer that lies ranging from 100 days to more than
See also magnitude. between the core and the crust of a 500 days. See also variable star. New General Catalogue (NGC)
rocky (Earth-like) planet or a major A catalogue of nebulae, clusters, and
lunar eclipse see eclipse. planetary satellite. See also core, crust. molecular cloud A cool, dense cloud galaxies that was published in 1888
of gas and dust in which the by the Danish astronomer John L.E.
M mare (plural: maria) A relatively temperature is sufficiently low to Dreyer. Objects in this catalogue are
smooth, dark, lava-filled basin on enable atoms to join together to denoted by “NGC” followed by a
MACHO An acronym for MAssive the surface of the Moon.The name form molecules such as molecular number. For example, the
Compact Halo Object, a very low- derives from the Latin for “sea”. hydrogen (H2) or carbon monoxide Andromeda Galaxy is NGC
luminosity object – such as a planet, (CO), and within which conditions 224. See also Messier catalogue.
brown dwarf, exceedingly dim white massive compact halo object see are favourable for star formation.
dwarf, or a black hole – that exists in MACHO. Newton’s laws of motion Three laws
the halo of a galaxy but is usually too moon Also known as a natural satellite, a describing the behaviour of moving
faint to be seen directly. MACHOs meridian (1) A great circle on the body that orbits a planet. The Moon is bodies that were set out by Isaac
are believed to account for a surface of the Earth or another the Earth’s natural satellite. Orbiting Newton in 1687. Newton’s first law
relatively small proportion of the astronomical body that passes through the Earth at a mean distance of states that a body continues to move
unseen dark matter in a galaxy’s halo. the north and south poles and crosses 384,000km (239,000 miles) in a in a straight line at a constant speed
See also dark matter, halo. the equator at right angles. (2) A great period of 27.3 days, it has a diameter unless acted on by a force.The
circle on the celestial sphere that of 3,476km (2,159 miles). See also second law shows how a force causes
magnetic field The region of space passes through the north and south satellite. a body to accelerate in the direction
surrounding a magnetized body celestial poles and crosses the celestial along which an applied force is
within which its magnetic influence equator at right angles. An observer’s moon dog See sun dog. acting.The third law states that for
affects the motion of an electrically local meridian passes through the any force there is an equal and
charged particle. celestial pole, the zenith, and the multiple star A system consisting of opposite reaction force.
north and south points of the horizon. two or more stars bound together by
magnetosphere The region of space See also celestial sphere, great circle. gravity and revolving around each Newtonian gravity see gravity.
around a planet within which the other (a system of just two stars is also
motion of charged particles is Messier catalogue A widely used called a binary). See also binary star. nova (plural: novae) A star that
controlled by the planetary magnetic catalogue of nebulous objects (most suddenly brightens by a factor of
field rather than the solar wind and of them nebulae, star clusters, and N thousands or more, then fades back to
the associated interplanetary galaxies) that was published in 1781 its original brightness over a period of
magnetic field.The shape of a planet’s by the French astronomer Charles near-Earth asteroid see asteroid. weeks or months.The flare-up occurs
magnetosphere is influenced by the Messier. Objects contained in this when a fusion reaction is triggered on
solar wind, which squeezes it inwards catalogue are designated by the letter nebula (plural: nebulae) A cloud of the surface of a white dwarf by gas
on the Sun-facing side and drags it “M” followed by a number. For gas and dust in interstellar space.The flowing from a companion star.The
out to form an elongated “tail” (a example, M31 is the Andromeda name derives from the Latin for name derives from the Latin for
magnetotail) on the opposite, or Galaxy and M42 is the Orion Nebula. “cloud”.There are several types of “new”, because the rapid brightening
downstream, side. See also solar wind. See also New General Catalogue. luminous nebula (nebulae that shine). produces what appears to be a new
An emission nebula is a cloud of gas star. See also white dwarf, fusion.
magnification The increase in the meteor The short-lived streak of light and dust that contains one or more
apparent angular size of an object seen when a meteoroid plunges into extremely hot, young, high- nuclear bulge see spiral galaxy.
when viewed through an optical the Earth’s atmosphere and is heated luminosity stars; ultraviolet light
instrument, such as a telescope.The to incandescence by friction. A emitted by these stars causes the nuclear fusion see fusion.
magnification of a telescope is equal sporadic meteor is one that appears at a surrounding gas to glow. Nebulae of
to the focal length of its objective random time from a random direction. this kind are also called HII regions nucleus (plural: nuclei) (1) The
lens or primary mirror divided by the A meteor shower is a substantial number because they contain a large compact central core of an atom,
focal length of its eyepiece. of meteors that appear to radiate proportion of ionized hydrogen. A which consists of a number of
from a common point in the sky (the reflection nebula is observed when the positively charged protons and
magnitude (absolute and apparent) radiant) when the Earth is passing dust particles within a cloud are lit neutral neutrons.The nucleus of a
Apparent magnitude is a measure of the through a stream of meteoroids. See up by light from a neighbouring hydrogen atom consists of a single
apparent brightness of an object as also meteorite, meteoroid. bright star. Other types of luminous proton. (2) The solid, ice-rich body
seen in the sky.The fainter the nebulae include planetary nebulae of a comet. (3) The central core of
object, the higher the numerical meteorite A rocky or metallic (shells of gas puffed out by dying a galaxy, within which stars are
value of its magnitude.The faintest meteoroid that survives passage stars) and supernova remnants (the relatively densely packed together.
stars visible to the naked eye are of through the atmosphere and reaches debris of exploded stars). A dark
magnitude 6, whereas the brightest the Earth’s surface in one piece or in nebula (or absorption nebula) is a dust- O
objects in the sky have negative fragments. See also meteor, meteoroid. laden cloud that blocks out light
apparent magnitudes. A star said to be from background stars and appears as occultation The passage of one body
of 1st magnitude has a magnitude of meteoroid A lump or small particle of a dark patch in the sky. See also in front of another, which causes the
1.49 or less, a star of 2nd magnitude rock, metal, or ice orbiting the Sun diffuse nebula, HII region, planetary more distant one to be wholly or
has a value of 1.50 to 2.49, and so in interplanetary space. Meteroid sizes nebula, supernova. partially hidden.The term is usually
on. Absolute magnitude is the apparent range from a fraction of a millimetre used to describe the passage of a
magnitude a star would have if it (small fraction of an inch) to a few neutrino A fundamental particle of body of larger apparent size in front
metres (yards). Some are debris from exceedingly low mass, which has zero of a body of smaller apparent size –
collisions between asteroids. Others
are particles released by comets; these
spread out along cometary orbits to

glossary

for example, when the Moon passes parhelic circle See sun dog. prominence A flame-like plume of gas which is believed to be the most G U I DE TO T H E UGNLIOVSESRASREY
in front of a star or when a planet that follows magnetic field lines in luminous kind of active galactic
(such as Jupiter) passes in front of one parsec (pc) The distance at which a the solar atmosphere. An active or nucleus.The name is an abbreviation
of its moons. star would have an annual parallax eruptive prominence undergoes rapid for quasi-stellar radio source, but is
of one second of arc (one second of changes, whereas a quiescent also applied to quasi-stellar objects
Oort Cloud (Oort–Opik Cloud) A angular measurement). One parsec prominence remains suspended in the (QSOs), which are not strong radio
spherical distribution of trillions of is equivalent to 3.26 light-years, solar atmosphere for a prolonged emitters.
icy planetesimals and cometary nuclei or 30,900 billion km (19,200 billion period.
that surrounds the Solar System and miles). See also parallax. quiescent prominence see prominence.
extends out to a radius of about 1.6 proper motion The angular rate at
light-years from the Sun. It provides parselene See sun dog. which a star changes its observed R
the reservoir from which long-period position on the celestial sphere.
and “new” comets originate. Its penumbra (1) The lighter, outer part of Annual proper motion is the angle radial velocity The component of a
existence was proposed in 1950 by the shadow cast by an opaque body. (seldom more than a small fraction of body’s velocity that is along the line
Dutch astronomer Jan H. Oort (a An observer within the penumbra 1 second of angular measurement) of sight directly towards, or away
similar idea had also been suggested can see part of the illuminating through which a star appears to shift from, an observer.The radial velocity
by Estonian astronomer Ernst J. source. See also eclipse. (2) The less in the course of one year. of a celestial body can be obtained by
Opik). See also comet, planetesimal. dark and less cool outer region of a measuring the Doppler effect in its
sunspot. See also sunspot, umbra. protogalaxy A progenitor of a normal spectrum. See also Doppler effect, red
open cluster A loose cluster of up to galaxy.The building blocks from shift, spectrum.
a few thousand stars that lies in or perigee The point on its orbit at which galaxies were assembled
close to the plane of the Milky Way which a body that is revolving through a process of collisions and radiant The point in the sky from
galaxy. Member stars of each cluster around the Earth is at its closest mergers, protogalaxies are believed to which the tracks of meteors that are
formed from the same cloud of gas to the Earth. See also apogee. have formed a few hundred million members of a particular meteor
and dust, and have closely similar ages years after the Big Bang when clouds shower appear to radiate. See also
and chemical compositions. Clusters perihelion The point on its orbit at of gas collapsed under the action of meteor.
of this kind are also known as galactic which a planet, or other Solar System gravity.
clusters. See also globular cluster. body, is at its closest to the Sun. radio galaxy A galaxy that is
proton An elementary particle, exceptionally luminous at radio
open universe A universe in which phase The proportion of the visible composed of three quarks, that has a wavelengths. A typical radio galaxy
the average density is less than the hemisphere of the Moon or a planet positive electrical charge and is a contains an active galactic nucleus
critical density that is needed to halt that is illuminated by the Sun at any constituent of every atomic nucleus. from which jets of energetic charged
its expansion and which, therefore, particular instant. See also atom. particles are being propelled towards
will expand forever. See also closed huge clouds of radio-emitting
universe, flat universe, oscillating universe. photon An individual package, or proton–proton chain (pp chain) material that in many cases are much
quantum, of electromagnetic energy, A sequence of reactions that fuse larger than the visible galaxy. See also
opposition The position of a planet which may be envisaged as a together hydrogen nuclei (protons) to active galaxy.
when it is exactly on the opposite “particle” of light.The shorter the create helium nuclei.The net result
side of the Earth from the Sun. Its wavelength of the radiation and of the process is to convert four radio telescope An instrument that is
elongation is then 180°, and it is higher the frequency, the greater protons into one helium nucleus, designed to detect radio waves from
highest in the sky at midnight. the energy of the photon. See also which consists of two protons and astronomical sources.The most
See also conjunction, elongation. electromagnetic radiation. two neutrons.The proton–proton familiar type is a concave dish that
reaction is the dominant hydrogen- collects radio waves and focuses them
optical double star see double star. photosphere The thin, gaseous layer at burning process in stars similar to, or onto a detector.
the base of the solar atmosphere, less massive than, the Sun. See also
orbit The path of a body that is from which the Sun’s visible light is fusion, hydrogen burning, neutron, proton. red-dwarf star A cool, red, low-
moving within the gravitational field emitted and which corresponds to luminosity star that, when plotted
of another.The orbit of a planet the visible surface of the Sun. protoplanetary disc A flattened disc on a Hertzsprung–Russell diagram,
around a star or a satellite around a of dust and gas surrounding a newly is located towards the bottom end
planet will normally be an ellipse or, planet A body that is much less massive formed star and within which matter of the main sequence. See also
exceptionally, a circle (a circle is a than a star, revolves around a star, and may be aggregating together to form Hertzsprung–Russell diagram,
special case of an ellipse). shines by reflecting that star’s light. As the precursors of planets. See also main sequence.
a general guide, an orbiting body is planetesimal.
orbital period The period of time considered to be a planet (rather than red-giant star A large, highly luminous
during which a body travels once a brown dwarf) if its mass is less than protostar A star in the early stages of star with a low surface temperature
around its orbit.The sidereal orbital about 13 times the mass of Jupiter. formation. It consists of the central and a reddish colour. A red giant has
period is the time taken by one body See also brown-dwarf star. part of a collapsing cloud that is evolved away from the main
to revolve around another (for heating up and is accreting matter sequence, is “burning” helium in its
example, the Moon around the planetary nebula A glowing shell of from its surroundings, but within core rather than hydrogen, and is
Earth) measured relative to the gas ejected by a star at a late stage in which hydrogen fusion reactions have approaching the final stages of its
background stars. its evolution. not yet commenced. life. See also helium burning,
Hertzsprung–Russell diagram,
oscillating universe A universe that planetesimal One of the large number pulsar A rapidly rotating neutron star main sequence.
expands and contracts in a cyclic of small bodies, composed of rock or from which we receive brief pulses of
fashion.The collapse of such a ice, that formed within the solar radiation, at short and precisely timed red shift The displacement of spectral
universe at the end of one cycle nebula and from which the planets intervals, as it spins around its axis. lines to longer wavelengths that is
triggers a new Big Bang that initiates were eventually assembled through observed when a light source is
the next cycle. See closed universe, flat the process of accretion. pulsating variable see variable star. receding from an observer.The shift
universe, open universe. in wavelength is proportional to the
plasma A completely ionized gas state Q speed at which the source is
P of matter that consists of equal receding. Cosmological red shift is a
numbers of positively charged ions and quantum see photon. wavelength shift that is caused by the
parallax The apparent shift in position negatively charged electrons. Plasmas expansion of the Universe. See also
of an object when it is observed from usually have very high temperatures. quark A fundamental particle, the main blue shift, Doppler effect, spectral line.
different locations. Stellar parallax is Examples include the solar corona matter constituent of all atomic nuclei.
the apparent shift in position of a and solar wind, both of which consist Quarks join in bunches of three to red supergiant star An extremely
relatively nearby star when viewed predominantly of protons and make baryons (for example, protons large star of very high luminosity
from different points on the Earth’s electrons. See also corona, solar wind. and neutrons) or in quark–antiquark and low surface temperature. Stars
orbit. Annual parallax is the maximum pairs to form particles called mesons. of this kind are located towards
angular displacement of a star from its polar axis see equatorial mounting. See also antiparticle, baryon. the top-right corner of the
mean position due to parallax.The Hertzsprung–Russell diagram. See
greater the distance of a star, the positron see antiparticle. quasar A very compact but extremely also Hertzsprung–Russell diagram.
smaller its parallax. powerful source of radiation that is
precession A slow change in the almost star-like in appearance but
orientation of a rotating body’s axis
caused by the gravitational influence
of neighbouring bodies.The Earth’s
axis precesses around in a conical
pattern over a period of 25,800 years.

glossary

GLOSSARY reflecting telescope (reflector) A opposite (clockwise) direction.The sidereal orbital period see orbital period. reaches its greatest southerly
telescope that uses a concave mirror planets Venus, Uranus, and Pluto declination.This is the northern-
to collect light, reflect light rays to a exhibit retrograde rotation. sidereal time A time system based on hemisphere winter solstice (the
focus, and form an image of a distant the apparent rotation of the celestial summer solstice in the southern
object. rich cluster see galaxy cluster. sphere. Local sidereal time is defined hemisphere). See also celestial equator,
to be 0 hours at the instant the first declination, ecliptic.
reflection nebula see nebula. right ascension (RA) The angular point of Aries crosses an observer’s
distance, measured eastwards, between meridian.The sidereal day corresponds space-time The four-dimensional
refracting telescope (refractor) A the first point of Aries (where the Sun’s to the Earth’s axial rotation period combination of the three dimensions
telescope that uses a lens to refract path around the sky crosses the measured relative to the background of space (length, breadth, and height)
(bend) light rays in order to bring celestial equator from south to north) stars, and is equal to 23 hours 56 and the dimension of time.The
them to a focus and form an image and a celestial body. It is expressed in minutes 4 seconds of mean (civil) concept that time and space are
of a distant object. hours, minutes, and seconds of time, time. See also equinox, right ascension. intimately linked, rather than (as
where 1 hour is equivalent to an angle Newton had believed) being separate
regolith A layer of loose rock, rocky of 15°.Together with declination, it singularity A point of infinite density entities, was proposed in 1908 by
fragments, and dust that covers the specifies the position of a body on into which matter has been Hermann Minkowski and was
surface of a planet or planetary the celestial sphere. See also celestial compressed by gravity, and a point at incorporated into Albert Einstein’s
satellite. sphere, declination, ecliptic, equinox. which the known laws of physics theories of relativity. See also relativity.
break down.Theory implies that a
regular cluster see galaxy cluster. ring A flat distribution of small singularity exists at the centre of a special theory of relativity see relativity.
particles and lumps of material that black hole. See also black hole.
relativity Theories developed in the revolves around a planet, usually in spectral class A class into which a star
early part of the 20th century by the plane of its equator. A ring system solar cycle A cyclic variation in solar is placed according to the lines that
Albert Einstein to describe the nature consists of a number of concentric activity (for example, the production appear in its spectrum.The principal
of space and time and the motion of rings surrounding a planet.The of sunspots and flares), which reaches spectral classes, arranged in decreasing
matter and light.The special theory of planets Jupiter, Saturn, Uranus, and a maximum at intervals of about 11 order of temperature, are labelled O, B,
relativity describes how the relative Neptune each have a ring system. years. Because the polarity pattern of A, F, G, K, M and are subdivided into
motion of observers affects their magnetic regions on the Sun reverses numbers from 0 to 9. For example, the
measurements of mass, length, and rocky planet A planet (also called a every 11 years or so, the overall spectral class of the Sun is G2. See
time. One of its consequences is that terrestrial planet) that is composed duration of the cycle is 22 years.The also luminosity, spectral line, spectrum.
mass and energy are equivalent.The mainly of rocks and has similar basic sunspot cycle is the 11-year variation
general theory of relativity treats gravity characteristics to the Earth.Within in the number (and overall area) of spectral line A feature that appears
as a distortion of space-time the Solar System, there are four rocky sunspots. See also solar flare, sunspot. at a particular wavelength in a
associated with the presence of planets: Mercury, Venus, Earth, and spectrum. An emission line is a bright
matter or energy. One of its Mars. See also gas planet. solar eclipse see eclipse. feature corresponding to the emission
consequences is that massive bodies of light at that wavelength, whereas
deflect rays of light. See also rupes Scarps or cliffs on the surface of solar flare A violent release of huge an absorption line is a dark feature
gravitational lensing, space-time. a planet or a satellite. See also moon. amounts of energy – in the form of corresponding to the absorption of
electromagnetic radiation, subatomic light at that wavelength. See also
resonance A gravitational interaction S particles, and shock waves – from a spectrum.
between two orbiting bodies that site located just above the surface of
occurs when the orbital period of satellite A body that revolves around the Sun. spectroscopic binary see binary star.
one is an exact, or nearly exact, simple a planet, otherwise known as a
fraction of the orbital period of the “moon”. An artificial satellite is an solar mass A unit of mass equal to the spectroscopy The science of obtaining
other. For example, Jupiter’s moon Io object deliberately placed in orbit mass of the Sun, which provides a and studying the spectra of objects.
is in a 1:2 resonance with another of around the Earth or around another convenient standard for comparing Because the detailed appearance of a
Jupiter’s moons, Europa (Io’s period Solar System body. the masses of stars. One solar mass is spectrum is influenced by factors such
is half of Europa’s period).When a equivalent to 1.989 x 1030 kg (1.96 x as chemical composition, density,
small object is in resonance with Schmidt–Cassegrain telescope A 1027 tons). Stellar masses range from temperature, rotation, velocity,
a more massive one, it experiences a telescope combining features of the about 0.08 solar masses up to about turbulence, and magnetic fields,
periodic gravitational tug each time Schmidt camera and the Cassegrain 100 solar masses. spectroscopy can reveal a wealth of
one of the bodies overtakes the other, telescope. Light enters the telescope information about the physical and
the cumulative effect of which tube through a thin corrector lens solar nebula The cloud of gas and dust chemical properties of, and processes
gradually changes its orbit. and is reflected from a concave mirror from which the Sun and planets occurring in, planets, stars, gas clouds,
at the bottom of the tube towards a formed. As the cloud collapsed, most galaxies, and other kinds of celestial
retrograde motion (1) The apparent small convex mirror fixed to the of its mass accumulated at the centre bodies. See also spectrum.
backward motion of a planet, from inner face of the correcting lens. It is to form the Sun, whereas the rest
east to west relative to the then reflected back down the tube, flattened out into a disc within spectrum A beam of electromagnetic
background stars. For most of the through a hole in the concave mirror, which planets were assembled by the radiation spread out into its
time, a planet such as Mars or Jupiter to a focus.This is a popular, compact process of accretion. See also accretion, constituent wavelengths. A continuous
will move from west to east relative design for small and moderate-sized protoplanetary disc. spectrum is the unbroken spread of
to the stars (direct motion), but it will telescopes. See also Cassegrain telescope. wavelengths emitted by a hot solid or
appear to reverse direction each time Solar System The Sun together with liquid or a dense gas (the continuous
it is being overtaken by the Earth Schwarzschild radius see black hole. everything that revolves around it spectrum of sunlight appears to
(around the time of opposition). See (the planets and their satellites, human eyes as a rainbow band of
also opposition. (2) Orbital motion in semimajor axis see ellipse. asteroids, comets, meteoroids, gas, colours). A hot, low-density gas emits
the opposite direction to that of the and dust). light at particular wavelengths only;
Earth and the other planets of the Seyfert galaxy A spiral galaxy with an the resulting spectrum consists of
Solar System. (3) The motion of a unusually bright, compact nucleus solar wind A stream of fast-moving, bright emission lines, each of which
satellite along its orbit in the opposite that in many cases exhibits brightness charged particles (predominantly corresponds to one of the
direction to that in which its parent fluctuations. First identified by electrons and protons) that escapes wavelengths at which emission takes
planet is rotating. American astronomer Carl Seyfert in from the Sun and flows outwards place. If a low-density gas is
1943, Seyfert galaxies comprise one through the Solar System like a wind. silhouetted against a source of a
retrograde rotation The rotation of a of the several categories of active continuous spectrum, it absorbs light
body around its axis in the opposite galaxy. See also active galaxy. solstice One of the two points on the at certain wavelengths to produce a
direction to the rotational motion of ecliptic at which the Sun is at its series of dark absorption lines. A
the Earth, the Sun, and the majority shepherd moon A small natural maximum declination north or south typical star has an absorption-line
of the planets.Viewed from above its satellite that, through its gravitational of the celestial equator. On or around spectrum (a continuous spectrum with
North Pole, the Earth rotates around influence, confines orbiting particles 21 June each year, the Sun reaches its dark lines superimposed by its
its axis and revolves around the Sun, into a well-defined ring around a greatest northerly declination.This is atmosphere), whereas an emission
in an anticlockwise direction (direct planet. A pair of shepherd moons, the northern-hemisphere summer nebula has an emission-line spectrum.
rotation), whereas a planet with where one is slightly closer to the solstice (the winter solstice in the See also spectral line.
retrograde rotation spins in the planet than the other, can squeeze southern hemisphere). On or around
particles into particularly narrow rings. 22 December each year, the Sun

glossary

spiral arm A spiral-shaped structure Saturn, Uranus, and Neptune. See to refer to large-scale geological W G U I DE TO T H E UGNLIOVSESRASREY
extending outwards from the central also inferior planet. structures, and features resulting
bulge of a spiral or barred spiral from their movement, on planets wavelength The distance between two
galaxy. It consists of gas, dust, supermassive black hole see black hole. other than the Earth. See also successive crests or between two
emission nebulae, and hot convection, crust, mantle. successive troughs in a wave motion.
young stars, supernova (plural: supernovae)
A catastrophic event that destroys a tektite A small, rounded, glassy object WIMP The acronym for Weakly
spiral galaxy A galaxy that consists of star and causes its brightness to formed when a large meteorite or Interacting Massive Particle, one of a
a spheroidal central concentration of increase, temporarily, by a factor of asteroid strikes a rocky planet, range of postulated elementary
stars (the nuclear bulge) surrounded by around 1 million. A type II supernova melting the surface rocks and particles that have high masses (tens
a flattened disc composed of stars, occurs when the core of a massive throwing molten drops of rock into or hundreds of times as great as that
gas, and dust, within which the major star collapses and the rest of the star’s the atmosphere.Typically a few of a proton) but interact so
visible features are clumped together material is blasted away; the collapsed centimetres (inches) across, tektites exceedingly weakly with ordinary
into a pattern of spiral arms. See also core usually becomes a neutron star. have been shaped by their flight matter that they have not yet been
galaxy, spiral arm. A type Ia supernova involves the through the atmosphere. On the directly detected.WIMPs are widely
complete destruction of a white Earth’s surface, they are found in a considered to comprise the major
star A self-luminous body of hot dwarf.The expanding cloud of debris number of specific locations, called part of the dark-matter content of
plasma that generates energy by from a supernova is called a supernova strewn fields. See also asteroid, meteorite. the Universe. See also dark matter.
means of nuclear fusion reactions. remnant. See also neutron star, white
dwarf. terrestrial planet see rocky planet. white-dwarf star A star of low
starburst galaxy A galaxy within luminosity but relatively high surface
which star formation is taking place synchrotron radiation transit (1) The passage of a particular temperature that has ceased to
at an exceptionally rapid rate. Electromagnetic radiation that is celestial body across an observer’s generate energy by nuclear-fusion
emitted when electrically charged meridian. (2) The passage of a reactions, that has been compressed
star cluster A group of between a few particles (usually electrons) gyrate at body in front of a larger one (for by gravity to a diameter comparable
tens and around 1 million stars held very high speed around lines of force example, the passage of the planet to that of the Earth, and that is
together by gravity. All the member in a magnetic field. Synchrotron Venus across the face of the Sun, or slowly cooling and fading. See also
stars of a particular cluster are radiation has a characteristic a satellite across the face of a planet). black dwarf, Hertzsprung–Russell diagram.
thought to have formed from the continuous spectrum that is different
same original massive cloud of gas from that which is emitted by a star T Tauri star A young star, surrounded Wolf–Rayet star A very hot star
and dust.There are two principal or a black body. Astronomical sources by gas and dust, that varies in from which gas is escaping at an
types of cluster: open clusters and of synchrotron radiation include brightness and usually shows exceptionally rapid rate, which is
globular clusters. See also globular supernova remnants and radio evidence of a strong stellar wind (a surrounded by an expanding gaseous
cluster, open cluster. galaxies. See also black body, stream of gas flowing away from the envelope, and which has emission
electromagnetic radiation, spectrum. star).T Tauri stars are believed still to lines in its spectrum. See also emission
stellar-mass black hole see black hole. be contracting towards the main line, spectrum.
synchronous rotation The rotation sequence.They are named after the
stellar parallax see parallax. of a body around its axis in the same first star of this kind to be identified. XYZ
period of time that it takes to orbit See also main sequence, protostar.
stellar wind An outflow of charged another body. Synchronous rotation, X-ray burster An object that emits
particles from the atmosphere of a which is also known as captured UV strong bursts of X-rays, lasting from a
star. See also solar wind. rotation, is caused by tidal forces few seconds to a few minutes.The
acting between the two bodies. ultraviolet radiation Electromagnetic bursts are believed to occur when gas
sun dog One of a pair of coloured Because its rotational and orbital radiation with wavelengths shorter drawn from an orbiting companion
patches of light that sometimes may periods are the same, the orbiting than visible light but longer than star accumulates on the surface of a
be seen on either side of the Sun, body always keeps the same face X-rays.The hottest stars radiate neutron star and triggers a nuclear-
separated from the Sun by an angle turned towards the object around strongly at ultraviolet wavelengths. fusion chain reaction. See also fusion,
of about 22°. Otherwise known as a which it is revolving. Like most of neutron star.
parhelion or mock sun, a sun dog is the planetary satellites, the Earth’s umbra (1) The dark, central cone of
formed when ice crystals in the moon displays synchronous rotation. the shadow cast by an opaque body. X-ray radiation Electromagnetic
Earth’s atmosphere refract sunlight. A See also orbital period, satellite. The illuminating source will be radiation with wavelengths shorter
moon dog, or parselene, is a patch of completely hidden from view at any than ultraviolet radiation but longer
light that sometimes forms by the T point within the umbra. (2) The than gamma rays. X-rays are emitted
same process on either side of the darker, cooler central region of a by extremely hot clouds of gas, such
Moon. A parhelic circle is a large, tail (of a comet) A stream, or streams, sunspot, where the temperature is as the solar corona.
faint ring of white light, produced of ionized gas and dust that is swept about 1,500–2,000°C (about
by the reflection of sunlight from out of the head of a comet (the 2,700–3,600°F) cooler than the zenith The point on the sky directly
atmospheric ice crystals, which coma) when it approaches, and average for the solar surface. See above an observer (that is, 90° above
crosses the Sun, passes through a pair begins to recede from, the Sun. also eclipse, penumbra, sunspot. the observer’s horizon).
of sundogs, and extends around the A type I tail (or gas tail) consists of
sky. Although a complete circle may ionized gas driven out of the coma vacuum energy see cosmological constant. zodiac A band around the celestial
be seen occasionally, more usually it by the solar wind. A type II tail (or sphere that extends for 9° on either
is only possible to see arcs of light dust tail) is composed of dust Van Allen belts Two concentric side of the ecliptic, and through
extending outwards from the particles that have been swept out doughnut-shaped zones that contain which the Sun, Moon, and naked-
sundogs. of the coma by the pressure of charged particles (electrons and eye planets appear to travel.The
sunlight. See also comet. protons) trapped in the Earth’s zodiac contains part or all of 24
sunspot A patch on the surface of magnetic field.They were discovered constellations. In the course of the
the Sun that appears dark because it tectonic plate One of the large, rigid in 1958 by American space scientist year, the Sun passes through 13 of
is cooler than its surroundings. sections into which the Earth’s James Van Allen. these constellations, 12 of which
Sunspots occur in regions where lithosphere (which comprises the correspond to the astrological “signs
localized concentrated magnetic crust and the rigid uppermost layer variable star A star that varies in of the zodiac”. See also ecliptic.
fields impede the outward flow of of the Earth’s mantle) is divided. brightness. A pulsating variable is a
energy from the solar interior. See Carried along by slow convection star that expands and contracts in zodiacal light A faint, cone-shaped
also solar cycle. currents in the mantle, tectonic a periodic way, varying in brightness glow that extends along the direction
plates drift very slowly across the as it does so. An eruptive variable is a of the ecliptic from the western
supergiant An exceptionally luminous surface of the planet.Their relative star that brightens and fades abruptly. horizon after sunset or from the
star with a very large diameter. motions give rise to phenomena such A cataclysmic variable is a star that eastern horizon before sunrise. Most
Supergiant stars appear at the top of as earthquakes, volcanic activity, and suffers one or more major explosions easily seen from tropical skies, it is
the Hertzsprung–Russell diagram. mountain building.The term (for example, a nova). See also caused by the scattering of sunlight
See also Hertzsprung–Russell diagram. “tectonic” is sometimes also used Cepheid variable, nova. by particles of interplanetary dust that
lie close to the plane of the ecliptic.
superior conjunction see conjunction. vernal equinox see equinox.

superior planet A planet that travels volcanic crater see crater.
around the Sun on an orbit that is
outside the orbit of the Earth.The
superior planets are Mars, Jupiter,

index

INDEX

IGGNUUDIIEDDXEE TTOO TT HH EE UU NN II VV EE RRSS EE Page numbers in bold indicate Addams, Jane 137 Alpha (α) Aurigae (Capella) Alpha (α) Herculis (Ras Algethi) Alpha (α) Ursae Majoris
feature profiles or extended Addams Crater (Venus) 137 343 281, 348 (Dubhe) 68, 344
treatments of a topic. Page Adonis 209
numbers in italic indicate pages Adrastea 178, 180 sky guides 414, 415, 432, 468 Alpha (α) Horologii 403 Hertzsprung–Russell (H–R)
on which the topic is illustrated. AE Aurigae 392 Alpha (α) Boötis (Arcturus) Alpha (α) Hydrae (Alphard) 378 diagram 230
Celestial objects whose names Aeneas Crater (Dione) 193
begin with a number can be aerogel 219, 219 344, 347 Hertzsprung–Russell (H–R) Alpha (α) Ursae Minoris
found at the end of the index. age Hertzsprung–Russell (H–R) diagram 230 (Polaris) 274–75, 338, 338,
344
A of Earth 92 diagram 230 in monthly sky guides 426,
of star clusters 285 in monthly sky guides 426, 427 circumpolar stars 332
A stars 231 of Universe 42 Hertzsprung–Russell (H–R)
AASTO project 297 Agena spacecraft 102, 102 432, 433, 438, 439, 444, Alpha (α) Leonis (Regulus)
AB Aurigae 233 Aglaonice Crater (Venus) 137 445, 450, 451, 456 249, 361 diagram 230
Abell, George 321 Air Pump see Antlia naked-eye astronomy 73 in monthly sky guides 432,
Abell 400 317 Airy Crater (Mars) 171 Alpha (α) Canis Majoris Hertzsprung–Russell (H–R)
Abell 1060 (Hydra Cluster) 320 Aitken Basin Crater (Moon) (Sirius A) 248, 376 diagram 230 438
Abell 1656 (Coma Cluster) ancient astronomy 82 naked-eye astronomy 73, 73
159 apparent magnitude 67 in monthly sky guides 427 Alpha (α) Virginis (Spica) 362
316, 317, 320, 324 Aitne 179 binary system 270 naked-eye astronomy 73 Hertzsprung–Russell (H–R)
Abell 1689 27, 316, 321 Akna Montes (Venus) 132 classification 231 name, origin of 68
Abell 2029 317 Albiorix 189 Hertzsprung–Russell (H–R) Alpha (α) Librae diagram 230
Abell 2065 (Corona Borealis Albireo (Beta (β) Cygni) 270, diagram 230 in monthly sky guides 426,
in monthly sky guides 414, (Zubenelgenubi) 363
Cluster) 321 273, 350, 350, 456 415, 421, 426, 427, 475, 481 Alpha (α) Lyrae (Vega) 249, 427, 432, 433, 438, 439,
Abell 2125 321 Alcmene 227 naked-eye astronomy 73 444, 445, 450, 451
Abell 2151 (Hercules Cluster) Alcor (80 Ursae Majoris) name, origin of 68 349, 350 naked-eye astronomy 73
Winter Triangle 420, 420, 480 circumstellar disc 290 Alpha (α) Vulpeculae 368
321, 348 272, 344, 345, 438 Alpha (α) Canis Minoris Hertzsprung–Russell (H–R) alphabet, Greek 7, 333
Abell 2218 23, 322–23 Alcott Crater (Venus) 137 (Procyon) 280, 376 Alphard (Alpha (α) Hydrae)
Abell S 373 (Fornax Cluster) 319 Alcyone (Eta (η) Tauri) classification 231 diagram 230 378
absolute magnitude 231 Hertzsprung–Russell (H–R) luminosity 231 Hertzsprung–Russell (H–R)
273, 287, 356 diagram 230 in monthly sky guides 432, diagram 230
absolute magnitude scale 67 Aldebaran (Alpha (α) Tauri) in monthly sky guides 420, in monthly sky guides 426,
Hertzsprung–Russell (H–R) 481 438, 444, 445, 450, 451, 427
252, 356 naked-eye astronomy 73 456, 457, 462, 463 Alpheca (Alpha (α) Corona
diagram 230 classification 231 Winter Triangle 420, 420, 480 naked-eye astronomy 73 Borealis) 444
main-sequence stars 247 Hertzsprung–Russell (H–R) Alpha (α) Canum Venaticorum Alpha (α) Mensae 406 Alpheratz (Alpha (α)
absorption lines 33, 33 (Cor Caroli) 346, 346 Alpha (α) Microscopii 387 Andromedae) 352, 370
Lyman Alpha lines 325, 325 diagram 230 Alpha (α) Capricorni 387 Alpha (α) Monocerotis 377 Alphonsus Crater (Moon) 155
stellar classification 231 and Hyades 286 Alpha (α) Centauri (Rigil Alpha (α) Orionis (Betelgeuse) Alrescha (Alpha (α) Piscium)
Académie des Sciences 88 in monthly sky guides 415, Kentaurus) 248, 382, 382 25, 252, 374, 376 372, 372
accelerating motion 40, 40 apparent magnitude 67 apparent magnitude 67 Alshain (Beta (β) Aquilae) 367
accretion discs 245 475 Hertzsprung–Russell (H–R) classification 231, 231 Altair (Alpha (α) Aquilae) 248,
black holes 263, 310 naked-eye astronomy 73 diagram 230 Hertzsprung–Russell (H–R) 350, 367, 367
young stars 237 Aldrin, Edwin “Buzz” 104, 104, in monthly sky guides 427, diagram 230 in monthly sky guides 445,
acetylene, on Jupiter 178 432, 433, 439, 439, 451, in monthly sky guides 415, 456, 457, 462, 463, 469
Achernar (Alpha (α) Eridani) 154 457, 463 420, 481 naked-eye astronomy 73
Alexandria 84, 84 Alpha (α) Ceti (Menkar) 373 naked-eye astronomy 73 Altar see Ara
246, 390, 404 algae 53 Alpha (α) Circini 397 Winter Triangle 420, 420, 480 altazimuth mountings, telescopes
Hertzsprung–Russell (H–R) Algieba (Gamma (γ) Leonis) Alpha (α) Corona Borealis Alpha (α) Pavonis 408 76, 76
(Alpheca) 444 Alpha (α) Pegasi 370 aluminium, properties 29
diagram 230 361, 361 Alpha (α) Corvi 381 Alpha (α) Persei (Mirphak) aluminium-26 222
in monthly sky guides 421, Algol (Beta (β) Persei) 272, Alpha (α) Crucis (Acrux) 396, 230, 354, 480 AM 0644-741 292–93
439 Alpha (α) Persei Cluster 354, Amalthea 178, 179, 180
457, 463, 469, 475, 481 354, 354, 480 Alpha (α) Cygni (Deneb) 350 480 Amazon River (Earth) 146
Acheron Fossae (Mars) 168 ALH 81105 meteorite 223 Hertzsprung–Russell (H–R) Alpha (α) Piscis Austrini American Association of Variable
achromatic telescopes 76 aliens, search for 53, 53 diagram 230 (Fomalhaut) 249, 388, 388 Star Observers 281, 283
Acidalia Planum (Mars) 170 alignments, planetary 65 luminosity 231 Hertzsprung–Russell (H–R) amino acids 52
Acrux (Alpha (α) Crucis) 396, Alioth (Epsilon (ε) Ursae in monthly sky guides 444, diagram 230 Ammavaru Volcano (Venus) 135
451, 456, 457, 462, 463 in monthly sky guides 451, ammonia
439 Majoris) 68, 344 naked-eye astronomy 73 457, 462, 463, 468, 475, 481 interstellar medium 228
active galaxies 310–15 Alkaid (Eta (η) Ursae Majoris) Alpha (α) Delphini (Sualocin) Alpha (α) Piscium (Alrescha) Jupiter 178, 178
369 372, 372 Neptune 200
BL Lacertae 315 68, 344 Alpha (α) Eridani (Achernar) Alpha (α) Scorpii (Antares) Saturn 187, 187, 188
Centaurus A 312 Allende meteorite 222 246, 390, 404 252, 365, 386 Uranus 196, 197
Circinus Galaxy 312 Almaak (Gamma (γ) Hertzsprung–Russell (H–R) Hertzsprung–Russell (H–R) ammonium hydrosulphide, on
Cygnus A 314 diagram 230 diagram 230 Saturn 187
Fried Egg Galaxy 313 Andromedae) 273, 352 in monthly sky guides 421, in monthly sky guides 433, Amor asteroids 208, 208
M87 313 Almaaz (Epsilon (ε) Aurigae) 457, 463, 469, 475, 481 438, 444, 445, 445 analemma, Sun’s 60
NGC 1275 314 Alpha (α) Fornacis 389 Alpha (α) Serpentis (Unukalhai) Ananke 179
NGC 4261 313 277, 279, 279, 343 Alpha (α) Geminorum (Castor) 364 ancient astronomy 82–83
NGC 5548 313 Almach (Gamma (γ) 272, 358 Alpha (α) Tauri (Aldebaran) Andes (Earth) 143
PKS 2349 315 Hertzsprung–Russell (H–R) 252, 356 Andromeda 352
“supermassive” black holes Andromedae) 273, 352 diagram 230 classification 231 Almach (Gamma (γ)
Alnath (Beta (β) Tauri) 230, in monthly sky guides 420, Hertzsprung–Russell (H–R) Andromedae) 273, 352
297, 297 421, 427 diagram 230 Alpheratz (Alpha (α)
types of 310 343, 356 and Hyades 286 Andromedae) 352, 370
3C 48 315 Alnilam (Epsilon (ε) Orionis) in monthly sky guides 415, in monthly sky guides 474,
3C 273 315 475 474
Adams, John 90 230 naked-eye astronomy 73
Adams,W.S. 94 Alnitak (Zeta (ζ) Orionis) 230, Alpha (α) Triangulum Australis
Adams ring (Neptune) 201, 398
374, 375, 375
201 Alpha (α) Andromedae

(Alpheratz) 352, 370
Alpha (α) Aquilae (Altair) 248,

350, 367, 367
in monthly sky guides 445,

456, 457, 462, 463, 469
naked-eye astronomy 73
Alpha (α) Arietis 355

index

Andromeda cont. Ara (the Altar) cont. astronauts Aurora Australis 70, 70 Beta (β) Corvi 381 G U I DE TO T H E U N I VI NE RDSEEX
Upsilon (υ) Andromedae Mu (μ) Arae 291 future missions 111 Aurora Borealis 70, 70–71 Beta (β) Crucis (Becrux) 396
291, 291 Stingray Nebula 260 Moon landings 102–105 aurorae Beta (β) Cygni (Albireo) 270,
Space Race 100, 100
Andromeda Galaxy (M31, NGC Arabs space stations 106 Earth 70, 70–71, 123 273, 350, 350, 456
224) 301, 302–303, 352, 352 constellations 330 weightlessness 36 Jupiter 177, 177 Beta (β) Delphini (Rotanev)
early scientific astronomy 84, Saturn 187
binocular astronomy 75 85 astronomy Autonoe 179 369
Hooker Telescope 93 mythology 275 ancient astronomy 82–83 autumn equinox 61, 61, 138 Beta (β) Doradus 405
Local Group 318, 318 star names 330 binocular astronomy 74–75 Avebury 83 Beta (β) Geminorum (Pollux)
in monthly sky guides 468, computerized telescopes azimuth mountings, telescopes
Arago ring (Neptune) 201 78–79 358
469, 474, 475 Aratus of Soli 330 early scientific astronomy 76 Hertzsprung–Russell (H–R)
radio waves 34 Archer see Sagittarius 84–85 Azophi see al-Sufi
angular diameter 73 Arcturus (Alpha (α) Boötis) 18th- and 19th-century Aztecs 83 diagram 230
angular momentum 37 astronomy 90–91 in monthly sky guides 420,
animals 141 344, 347 from space 96, 97 B
Annefrank 210 Hertzsprung–Russell (H–R) naked-eye astronomy 72–73 421, 427
annular eclipses 63 radio astronomy 93, 93 b Puppis 393 Beta (β) Gruis 401
anorthite 223 diagram 230 telescope astronomy 76–77 B stars Beta (β) Leonis (Denebola) 68
anorthosite 125 in monthly sky guides 426, 20th-century astronomy Beta (β) Leonis Minoris 360
Ant Nebula (Menzel 3) 255 92–93 classification 231 Beta (β) Librae
Antarctica 432, 433, 438, 439, 444, Regor (Gamma (γ) Velorum)
AASTO project 297 445, 450, 451, 456 astrophotography 79, 79 (Zubeneschamali) 363
Ice-sheet 147 naked-eye astronomy 73 astrophysics 90 249 Beta (β) Lyrae (Sheliak) 277,
meteorites 147, 221 Arecibo radio telescope 53, 97 Astroplanner 78 Wolf–Rayet stars 251
Antares (Alpha (α) Scorpii) Arenal volcano (Earth) 143 Aten asteroids 208 Babylonians 349
Argo Navis 393, 394, 395, 420 Athos, Mount (Earth) 84 ancient astronomy 82, 83 Beta (β) Lyrae stars 277
252, 365, 386 argon Atlantic Ocean (Earth) 142 constellations 330 Beta (β) Monocerotis 277, 377
Hertzsprung–Russell (H–R) Earth’s atmosphere 140 Atlas 188, 287, 356 Bach Crater (Mercury) 127 Beta (β) Orionis (Rigel) 277,
Moon’s atmosphere 149 Atlas rockets 100 bacteria 52, 53, 141
diagram 230 Argonauts 394 atlases, star 331 Baghdad 85 374
in monthly sky guides 433, Argyre Planitia (Mars) 173 atmosphere (Earth) 140, 140 Baily, Francis 360 classification 231, 231
Ariadne 363 Baily’s Beads 63 Hertzsprung–Russell (H–R)
438, 444, 445, 445 Ariel 197, 199 aurorae 70, 70–71, 123 Balch, Emily 136
Antennae Galaxies (NGC 4038 Ariel 1 observatory 96 ice haloes 70, 70 Balch Crater (Venus) 136 diagram 230
Aries (the Ram) 355 moving lights and flashes 71, barium, formation of 51 in monthly sky guides 415
and 4039) 35, 307, 308, Alpha (α) Arietis 355 Barnard, Edward 180, 256 Beta (β) Pegasi 370
381, 381 Beta (β) Arietis 355 71 Barnard 33 (Horsehead Nebula) Beta (β) Persei (Algol) 272,
antielectrons see positrons Gamma (γ) Arietis 355, 355 noctilucent clouds 71, 71,
antimatter 31, 311, 311 Lambda (λ) Arietis 355 238, 239, 375, 375 354, 354, 480
antiparticles, Big Bang 46, 47, 48 Pi (π) Arietis 355 444 Barnard 68 24 Beta (β) Pictoris 290, 404, 404
antiquarks 31 sky guide 480 zodiacal light 71, 71 Barnard’s Galaxy (NGC 6822) Beta (β) Piscis Austrini 388
Big Bang 46, 47, 48 Arion 369 atmospheres Beta Regio (Venus) 133
Antlia (the Air Pump) 380 Aristarchus 84, 85, 86 formation of 233 318 Beta (β) Sagittarii 384
Zeta (ζ) Antliae 380 Aristarchus Crater (Moon) 154 Jupiter 178, 178 Barnard’s Merope Nebula 287 Beta (β) Scorpii 386
aperture Aristotle 59, 59, 84, 85 Mars 161, 161 Barnard’s Star 66, 230, 365 Beta (β) Tauri (Alnath) 230,
binoculars 74 arms, spiral galaxies 295 Mercury 125, 125 barred spiral galaxies 26, 294
telescopes 77, 77 Armstrong, Neil 104, 104, 154 Moon 149, 149 343, 356
Aphrodite 372 Arp 220 299 Neptune 200, 200, 201, 201 NGC 1530 26 Beta (β) Tucanae 402
Aphrodite Terra (Venus) 131, 135 Arp-Madore 1 (AM1) 403 old stars 234 NGC 6782 308 Beta (β) Ursae Majoris (Merak)
Apollinaris Patera (Mars) 168 Arrow see Sagitta Pluto 204 baryons 31
Apollo asteroids 208, 208 Arsia Mons (Mars) 164 Saturn 187, 187 al-Battânî 85 68, 73, 344
Apollo missions 102–105, 150, Artemis Chasma (Venus) 135 Sun 123, 123 Bayer, Johann 68, 331, 333 Betelgeuse (Alpha (α) Orionis)
153, 154, 156, 249 Artemis Corona (Venus) 135 Titan 194 Bayeux Tapestry 218
Apollo–Soyuz mission 105, 105 Asclepius 365, 365 Uranus 197, 197 Be stars 281 25, 252, 374, 376
apparent magnitude 67, 231 Ascraeus Mons (Mars) 164 Venus 129, 129 Beardmore Glacier (Earth) 147 apparent magnitude 67
April sky guide 432–37 Asellus Australis 359 atomic bomb 39 Becrux (Beta (β) Crucis) 396 classification 231, 231
Apus (the Bird of Paradise) 407 Asellus Borealis 359 atomic number, chemical Beehive Cluster (M44) 286, Hertzsprung–Russell (H–R)
Delta (δ) Apodis 407 asterisms 68
Theta (θ) Apodis 407 asteroids 25, 208–13 elements 29 359, 359 diagram 230
Aquarius (the Water Carrier) Annefrank 210 atoms 24, 28, 28–29 in monthly sky guides 420, in monthly sky guides 415,
371 asteroid belt 210
Eta (η) Aquarii 371, 439 Ceres 211 after Big Bang 50 421, 426 420, 481
Gamma (γ) Aquarii 371 collisions 209, 209 Big Bang 46 Beethoven region (Mercury) 127 naked-eye astronomy 73
Helix Nebula 253, 371, 371, computerized telescopes 78 in chemical compounds 29, Belinda 197 Winter Triangle 420, 420, 480
463 Eros 212–13 Bell, Jocelyn 94 Bethe, Hans 95
in monthly sky guides 469, formation of 233 29 Bellatrix (Gamma (γ) Orionis) BHR 71 238
469, 475 formation of Moon 149, 149 of chemical elements 29 Bianca 197
Pi (π) Aquarii 371 Gaspra 210 emergence of matter 48, 49 67 Big Bang 22, 46–49, 93, 96
Saturn Nebula 251, 371, 371, Ida 211 forces 30, 30 Bellerophon 370 aftermath of 50
463 impact craters on Moon 151 ionization 28 Belyaeyev, Pavel 101 cosmic microwave
Zeta (ζ) Aquarii 371 Mathilde 210 in molecules 29 Belz Crater (Mars) 172
Aquila (the Eagle) 367 orbits 118, 119, 208, nuclear fission and fusion 31, Berenice’s Hair see Coma background radiation
Alshain (Beta (β) Aquilae) 367 208–209 (CMBR) 34, 49, 50, 96,
see also Altair (Alpha (α) space probes 111 31 Berenices 325
Aquilae) structure 208 AU Microscopii 290 Bergerac, Cyrano de 98 distribution of galaxies 298
Eta (η) Aquilae 282, 367 Toutatis 210 August sky guide 456–58 Bessel, Friedrich 248 expanding space 42
Lambda (λ) Aquilae 367 Vesta 210 Augusta family, asteroids 210 Beta (β) Aquilae (Alshain) 367 fate of Universe 54
sky guide 456 Asterope 287, 357 Auriga (the Charioteer) 343, Beta (β) Arietis 355 galaxy superclusters 325
Tarazed (Gamma (γ) Aquilae) astrobiology 97 Beta (β) Camelopardalis 342 inflation theory 46, 46
367, 367 astrolabes 85, 85 414, 420, 421, 426, 480, 481 Beta (β) Canum Venaticorum particle physics 31
15 Aquilae 367 astrology 60, 63, 83 AB Aurigae 233 recreating conditions 47
57 Aquilae 367 astrometric binaries 270 AE Aurigae 343, 343, 392 346 Big Chill 54, 54, 55
Aquila Rift, Milky Way 229 Almaaz (Epsilon (ε) Aurigae) Beta (β) Capricorni 387 Big Crunch 54, 55, 55
Ara (the Altar) 399 Beta (β) Centauri (Hadar) 248, Big Dipper see Plough
277, 279, 279, 343 Big Rip 54, 55
see also Capella (Alpha (α) 382 binary pulsars 270
apparent magnitude 67 binary stars 270
Aurigae) in monthly sky guides 427, Alpha (α) Herculis (Ras
Zeta (ζ) Aurigae 343 Algethi) 281
432, 433, 439, 439, 451, Beta (β) Lyrae (Sheliak) 277
457, 463 black holes 263
eclipsing binary stars 270,
270, 354

index

IGGNUUDIIEDDXEE TTOO TT HH EE UU NN II VV EE RRSS EE binary stars cont. Bode, Johann Elert 304, 331, calderas, Martian volcanoes carbon cont. celestial poles 421
Epsilon (ε) Aurigae (Almaaz) 344 164, 165, 168, 168 main-sequence stars 246 Celestial Police 209
277 in meteorites 223 celestial sphere 58–59, 330
Eta (η) Geminorum (Propus) Bode’s Galaxy (M81, NGC calendar, ancient astronomy 82, in old stars 234, 251
280 3031) 304, 344, 344 83 supergiant stars 250 constellations 68
Izar (Epsilon (ε) Bootis) 273 Type I supernovae 279 mapping 332–37
Lambda (λ) Tauri 280 Bohr, Niels 29 Caliban 197, 199 Wolf–Rayet stars 251 motion of planets 64–65
M40 273 Bok globules 236, 236 California Extremely Large motion of stars 66
novae 278, 278 carbon dioxide Centaur see Centaurus
Polaris 274–75 BHR 71 238 Telescope (CELT) 35 atomic structure 29 Centaurs 206
Porrima 249 Cone Nebula 240 Callirhoe 179 in comets 215 Centaurus (The Centaur) 382
Type I supernovae 279, 279 Eagle Nebula 242 Callisto 25, 178, 185, 193 interstellar medium 228 IC 2944 244
Wolf–Rayet stars 251 IC 2944 244, 244 on Mars 161, 169, 171, 171 see also Alpha (α) Centauri
Zeta (ζ) Boötis 273 Lagoon Nebula 241, 241 space probes 110 on Venus 129
15 Monocerotis 276 bolometric luminosity 231 Callisto, in mythology 345 (Rigil Kentaurus); Hadar
bomb, atomic 39 Caloris Basin (Mercury) 126, carbon monoxide (Beta (β) Centauri)
binocular astronomy 74–75 Bondi, Hermann 96 in comets 215 in monthly sky guides 415,
biosphere, Earth 141 bonds, states of matter 30 126, 127 on Pluto 204 421, 426, 433, 438, 445
Biosphere 2 111, 111 Boötes (the Herdsman) 347 Calypso 188, 192 Omega Centauri 75, 284,
Bird of Paradise see Apus see also Arcturus (Alpha (α) Camelopardalis (the Giraffe) carbon stars 231, 252, 252 285, 286, 288, 382, 402,
BL Lacertae (BL Lac) 315, 353 carbonaceous (C-type) asteroids 433, 439, 445
BL Lacertae objects see blazars Boötis) 342 Proxima Centauri 22, 230,
black dwarfs 233, 235, 262 Gamma (γ) Boötis 444 Beta (β) Camelopardalis 342 208 248, 382
Black Eye Galaxy (M64, NGC Izar (Epsilon (ε) Boötis) 25, 11 Camelopardalis 342 carbonaceous chondrite (stony) RCW 49 245
12 Camelopardalis 342 Centaurus A (NGC 5128) 14,
4826) 304, 360, 360 273, 347, 347, 444 cameras 79, 79 meteorites 208 312, 382
black holes 24, 25, 26, 233, 263 Kappa (κ) Boötis 347 Cancer (the Crab) 359 cardinal points 83 collision with spiral galaxy
Mu (μ) Boötis 347 see also Beehive Cluster Carina (the Keel) 395 308, 311, 314
accretion discs 263, 310 NGC 5548 313 Delta (δ) Canceri 359, 359 in monthly sky guides 439,
active galaxies 310, 310–11 Nu (ν) Boötis 347 Gamma (γ) Canceri 359, 359 see also Canopus (Alpha (α) 445
Andromeda Galaxy 302, 302 Xi (ξ) Boötis 347 Iota (ι) Canceri 359 Carinae) Cepheid variable stars 282
Big Chill 55 Zeta (ζ) Boötis 273 in monthly sky guides 420, measuring distances with 42,
Cygnus X-1 268 Bopp,Thomas 218 Epsilon (ε) Carinae 395 303, 303
discovery 94 Borrelly, Comet 215, 215, 219 426, 433 Eta (η) Carinae 245, 252, pulsation 278, 278
event horizon 41, 263 bosons 30, 30, 31 Zeta (ζ) Canceri 359 in Small Magellanic Cloud
formation 234, 234, 235 Big Bang 46 Cancer,Tropic of 61 258, 395, 395, 427, 433 301
galaxies 297, 297 bow shock Candor Chasma (Mars) 166, Iota (ι) Carinae 395 Cepheus 340
GRO J1655-40 268 Orion Nebula 20–21 in monthly sky guides 415, Delta (δ) Cephei 282, 340,
hypernovae 51 solar wind 139 167 340, 462
lensing 263, 269 Brahe,Tycho 87, 87, 88, 268, Canes Venatici (the Hunting 420, 426 Epsilon (ε) Cepheus 340
MACHO 96 269 Sher 25 261 IC 1396 241
matter 28 268 Dogs) 346 Theta (θ) Carinae 395, 427 Lambda (λ) Cepheus 340
Milky Way 14, 226 Tycho’s Supernova 268 Beta (β) Canum Venaticorum Carina Nebula (NGC 3372) Mu (μ) Cephei (Garnet Star)
radiation 34 Brahms Crater (Mercury) 127 230, 241, 241, 250, 283,
singularity 26, 41 Braun,Wernher von 99, 102 346 24, 245, 395, 395 340, 340
space-time 41 brightness, stars 67 Cor Caroli (Alpha (α) Canum in monthly sky guides 427, Zeta (ζ) Cepheus 340
SS 433 26 see also luminosity Ceres 90, 208, 209, 211
stellar black holes 26, 26 Britain, observatories 88 Venaticorum) 346, 346 433, 433 CERN (European Centre for
supermassive black holes 26, Brocchi’s Cluster 368, 368 La Superba (Gamma (γ) Carlyle,Thomas 329 Nuclear Research) 47
Broglie, Louis de 33 Carme 179 Cernan, Eugene 104, 105
26, 55, 297, 297 bromine, properties 29 Canum Venaticorum) 346 Cartwheel Galaxy (ESO 350- Cerro Tololo Inter-American
black smokers 142 Brontë Crater (Mercury) 127 see also Whirlpool Galaxy Observatory 258
Blake,William 89 Bronze Age 287 Canis Major (the Greater Dog) G40) 309 CETI (communication with
blazars 310, 310 Brown, Mike 207 Caspian Sea (Earth) 147 extraterrestrial intelligence)
brown dwarfs 25 376 Cassini, Giovanni 88 53
BL Lacertae (BL Lac) 315, discovery 94, 94 HD 56925 260 Cetus (the Sea Monster) 373
353 extra-solar planets 291 see also Sirius A (Alpha (α) Saturn’s moons 192, 193, 195 Gamma (γ) Ceti 373
formation 232 Cassini Regio (Iapetus) 195, Menkar (Alpha (α) Ceti) 373
distribution 311 Gliese 229b 25 Canis Majoris); Sirius B Mira (Omicron (ο) Ceti)
superluminal jets 311, 311 Bruno, Giordano 87 Tau (τ) Canis Majoris 376, 195 281, 373, 474, 475, 475
Blaze Star (T Coronae Borealis) Bubble Nebula 286 Cassini spacecraft 110, 110, in monthly sky guides 469,
bubble nebulae,Wolf–Rayet stars 376 474, 475, 480
282 UW Canis Majoris 376 194, 194 Tau (τ) Ceti 230, 373
blink comparators 205 260 Canis Major Dwarf 300 Cassiopeia 341 ZZ Ceti 230
Blinking Planetary 351 Bug Nebula (NGC 6302) Canis Minor (the Little Dog) Chaffee, Roger 249
blue jets 71, 71 Eta (η) Cassiopeiae 341 Chaldene 179
blue light, photoelectric effect 256–57 330, 376 Gamma (γ) Cassiopeiae 281, Chamaeleon (the Chameleon)
Bull see Taurus see also Procyon (Alpha (α) 407
32, 32 Burns Cliff (Mars) 174, 174, 341 Delta (δ) Chamaeleontis 407
Blue Planetary 382 Canis Minoris) M52 286, 341, 341, 468 Chameleon see Chamaeleon
blue shift 33, 33 175 Canopus (Alpha (α) Carinae) in monthly sky guides 414, Chandra X-ray Observatory
Blue Snowball (NGC 7662) Butterfly Cluster (M6, NGC 35, 268
376, 395 420, 474, 480 Chandrasekhar, S. 94
352, 352, 468 6405) 286, 386, 386 Hertzsprung–Russell (H–R) Phi (φ) Cassiopeiae 341 Chandrasekhar limit 262
blue supergiants in monthly sky guides 445, Rho (ρ) Cassiopeiae 341 charge-coupled device (CCD)
diagram 230 Tycho’s Supernova 268 detectors 79, 79
Eta (η) Carinae 258 445, 451, 457 in monthly sky guides 415, Cassiopeia, Queen 341, 352 charged particles
evolution 233 Butterfly Nebula (Hubble 5) Cassiopeia A (SN 1680) 51, aurorae 70, 123
HDE 226868 268, 268 427, 433, 469, 475, 481 ions 28
Sher 25 261 251 Canyon Diablo meteorite 222 264, 269 Jupiter 177
blue variable stars canyons, on Mars 166–67, Castor (Alpha (α) Geminorum) magnetic fields 247
Pistol Star 261 C
blue-white stars 166–67 272, 358
Regor (Gamma (γ) Velorum) C153 321 Capella (Alpha (α) Aurigae) Hertzsprung–Russell (H–R)
Cacciatore, Niccolò 369
249 Caelum (the Chisel) 389 343 diagram 230
Regulus (Alpha (α) Leonis) in monthly sky guides 414, in monthly sky guides 420,
Gamma (γ) Caeli 389
249 Calabash Nebula 415, 432, 468 421, 427
blueberries, Martian 175, 175 Capricorn,Tropic of 61 catalogues
BM Scorpii 286, 386 (OH231.8+4.2) 258 Capricornus (the Sea Goat)
Calabi-Yau spaces 41 nebulous objects 69
calcium, on Mercury 125 387, 462 stars 68, 330
Alpha (α) Capricorni 387 Cat’s Eye Nebula (NGC 6543)
Beta (β) Capricorni 387
carbon 254, 339, 339
atomic number 29 cD galaxies 296, 299, 316, 316,
carbon cycle (CNO cycle)
317
246 Celaeno 287
dust 24 celestial coordinates 59
formation of 51, 95 celestial cycles 60–63, 82
interstellar medium 228 celestial globes 330–31
and life 52 celestial meridian 59

index

charged particles cont. Cold Bokkeveld meteorite 223 contact binary systems 270 Crater (the Cup) 68, 381, 426 December sky guide 480–85 G U I DE TO T H E U N I VI NE RDSEEX
pulsars 263 Cold War 98 convection 246 craters see impact craters; declination 59, 59, 73
solar wind 123, 139 collapsing stars 235, 262 convection cells Deep Space 1 mission 219
Sun 122 Collins, Michael 104, 104 volcanoes Degas Crater (Mercury) 127
Collins, Peter 74, 74, 283 red giants 250 Crescent Nebula (NGC 6888) degrees of angle 73
Charioteer see Auriga collisions, galaxies 237, 237, Sun 95, 122 Deimos 163, 163
Charitum Montes (Mars) 173 convection currents 255 Delphinus (the Dolphin) 369
Charles I, King of England 346 299, 308, 308 Jupiter 178 Cressida 197
Charles II, King of England 88 colour force 30 plate tectonics 140 CRL 2688 (Egg Nebula) 254 Delta (δ) Delphini 369
Charon 204, 205, 205 colours, stars 66–67, 231 coordinates, celestial 59 Crow see Corvus Gamma (γ) Delphini 369
charts, star 331 Columba (the Dove) 392 Copernicus, Nicolaus 86–87 crust Rotaney (Beta (β) Delphini)
Chasma Boreale (Mars) 169 Copernicus Crater (Moon)
chasmata, on Mars 166–67 Mu (μ) Columbae 392 Earth 138, 138, 140, 140 369
chemical compounds 29, 29 coma, comets 215 149, 151, 155 Mars 160 Sualocin (Alpha (α) Delphini)
chemical elements see elements Coma Berenices (Berenice’s Coprates Chasma (Mars) 167 Moon 148
Chéseaux, Philippe Loys de 242 Cor Caroli (Alpha (α) Canum Crux (the Southern Cross) 396 369
China Hair) 360 Acrux (Alpha (α) Crucis) Delta (δ) Apodis 407
Black Eye Galaxy 304, 360, Venaticorum) 346, 346 Delta Aquarid meteor shower
ancient astronomy 82, 83 Cordelia 197, 197, 198 396, 439
and Polaris 275 360 core Becrux (Beta (β) Crucis) 396 451
space programme 111 Gamma (γ) Comae Berenices Gacrux (Gamma (γ) Crucis) Delta (δ) Canceri 359, 359
Chiron 206, 206 Earth 138, 138, 139 Delta (δ) Cephei 282, 340, 340,
in mythology 382 360 Jupiter 176, 176 230, 396
Chisel see Caelum Malin 1 309 Mars 160, 160 see also Jewel Box (Kappa (κ) 462
chondrites 222, 223 the Mice 308 Mercury 125, 125 Delta (δ) Chamaeleontis 407
chondrules 222, 223, 223 Coma Cluster (Abell 1656) Moon 148, 148 Crucis) Delta (δ) Corvi 381
Christmas Tree Cluster 240 Neptune 200, 200 in monthly sky guides 421, Delta (δ) Delphini 369
chromatic aberration 89 316, 317, 320, 324 Pluto 204 Delta (δ) Gruis 401, 401
chromosphere (Sun) 123, 123 Coma Star Cluster (Melotte Saturn 186 427, 432, 433, 438, 439, 445 Delta (δ) Librae 363
Chryse Planitia (Mars) 166 Uranus 196, 196 Mu (μ) Crucis 396 Delta (δ) Lyrae 349
Churyumov, Klim 219 111) 360, 432, 438 Venus 128, 128 naked-eye astronomy 73 Delta (δ) Octantis 409
Churyumov–Gerasimenko, Comas Solá, Comet 219 Coriolis effect 140, 140, 178 Pointers 248 Delta (δ) Orionis 374
“comet clouds” 309 corona, Sun 10, 63, 122, 123, Culann Patera (Io) 182 Delta (δ) Scorpii 386
Comet 219 comets 25, 214–19 Cunitz Crater (Venus) 136 Delta (δ) Scuti 366
Cigar Galaxy (M82, NGC 3034) 123 Cup see Crater Delta (δ) Serpentis 364
binocular astronomy 74 Corona Australis (the Southern Curtis, Heber 92, 93 Delta (δ) Telescopii 400
69, 297, 304, 344 Borrelly 215, 215, 219 cycles, celestial 60–63, 82 Delta (δ) Ursae Majoris 344
Circinus (the Compasses) 397 Churyumov–Gerasimenko 219 Crown) 399 Cygnus (the Swan) 350–51 Delta (δ) Velorum 394
Comas Solá 219 Gamma (γ) Coronae Australis Albireo (Beta (β) Cygni) Deneb (Alpha (α) Cygni) 350
Alpha (α) Circini 397 computerized telescopes 78
Circinus Galaxy (ESO 97-G13) Encke 214, 217 399 270, 273, 350, 350, 456 Hertzsprung–Russell (H–R)
formation 233 Kappa (κ) Coronae Australis Crescent Nebula 255 diagram 230
312 Giacobini-Zinner 219 Cygnus A (3C 405) 314, 351
Circlet 372, 372, 468, 469 Great Comet of 1680 216 399 Cygnus X-1 94, 268, 351 luminosity 231
circulation cells, Jupiter 178, Hale–Bopp 214, 216, 218 RX J1856.5-3754 264 see also Deneb (Alpha (α) in monthly sky guides 444,
Halley’s Comet 89, 90, 90, Corona Borealis (the Northern
178 Cygni) 451, 456, 457, 462, 463
Circumnuclear Disc, Milky Way 111, 111, 214, 215, 216, Crown) 363, 444 DR 6 241 naked-eye astronomy 73
218, 439 Abell 2065 (Corona Borealis DR 21 244 Denebola (Beta (β) Leonis) 68
229 Hyakutake 74, 207, 214, 217, in monthly sky guides 456, density waves
circumstellar discs, formation of 218 Cluster) 321 formation of stars 232
Ikeya–Seki 216 Alpheca (Alpha (α) Corona 474, 480 spiral galaxies 227, 237, 295
planets 233, 233, 290–91, Ikeya–Zhang 25 Nova Cygni 1992 283 Desdemona 197
290 Kuiper Belt 206 Borealis) 444 Omicron (ο) Cygni 350 deserts, on Earth 141, 141
CL0024+1654 323 life cycles 215 Nu (ν) Coronae Borealis 363 TT Cygni 252 Desktop Universe 78
CL-2244-02 317 meteoroids 220 R Coronae Borealis 279, 56 Cygni 68 Despina 201
Claritas Fossae (Mars) 168 Oort Cloud 207 61 Cygni 230, 248, 351 deuterium 49
Clarke, Arthur C. 106, 106 orbits 214, 214 283, 363 Cygnus Loop (NGC 6960/95) Devana Chasma (Venus) 133
classification Shoemaker–Levy 9 179, 179, Sigma (σ) Coronae Borealis Dido Crater (Dione) 193
galaxies 294, 294 219 228, 265 differential rotation, spiral
stars 231 Soho-6 215 363 Cygnus Rift 351, 456
Clementine space probe 151, space probes 111, 111 T Coronae Borealis (Blaze Cygnus Star Cloud 268 galaxies 294
152 structures 215, 215 digital astrophotography 79, 79
Cleopatra Crater (Venus) 136 Swift–Tuttle 214, 216, 220 Star) 282 D dimensions
climate, Earth 138 Tempel–Tuttle 214, 220 Zeta (ζ) Coronae Borealis
clocks, medieval astronomy 86 West 217 Dactyl 211, 211 Calabi-Yau spaces 41
closed universe 55, 55 Wild 2 111, 219 363 Daedalia Planum (Mars) 168 space-time 39
clouds Wirtanen 111, 111, 219 coronal mass ejections (CMEs), Dali Chasma (Venus) 135 Dione 188, 189, 190, 193
see also gas clouds compact groups Danilova Crater (Venus) 137 Discovery Rupes (Mercury)
Jupiter 178, 178, 179 Seyfert’s Sextet 319 Sun 122, 123, 123 Dante Alighieri 182
lenticular clouds 71 Stephan’s Quintet 320 Corvus (the Crow) 381 dark ages 50 127
Mars 161 Compass see Pyxis dark energy 27, 50, 54–55, 54 disrupted spiral galaxies
see also molecular clouds Compasses see Circinus Alpha (α) Corvi 381 dark galaxies 316
Neptune 201 composite particles 31 Antennae Galaxies 35, 307, dark matter 27, 28, 50 Antennae Galaxies 307
noctilucent clouds 71, 71, 444 compounds, chemical 29, 29 Cartwheel Galaxy 309
Uranus 197, 197 Compton Gamma Ray 308, 381, 381 dwarf elliptical galaxies 296 ESO 510-G13 308
Venus 129, 129 Observatory 35 Beta (β) Corvi 381 galaxies 298 the Mice 308
Clownface Nebula 358 computerized telescopes 78–79 Delta (δ) Corvi 381 galaxy superclusters 325 distance
clusters see galaxy clusters; galaxy Cone Nebula (NGC 2264) Epsilon (ε) Corvi 381 gravitational lensing 323 apparent magnitude 231
superclusters; star clusters 240, 276, 377, 377 Gamma (γ) Corvi 381 Milky Way 229 early scientific astronomy 84,
CMBR see cosmic microwave conjunction, planets 64, 65, 65 cosmic light horizon 23 dark nebulae 24, 228, 238
background radiation Constantine, Emperor 65 cosmic microwave background Barnard 68 24 84
Coalsack Nebula 396, 396, 397 constellations 68, 68–69, 328–409 BHR 71 238 expanding space 42–43
in monthly sky guides 433, see also individual constellations radiation (CMBR) 34, 49, Cone Nebula 240 mapping the Universe 324
439, 439, 445 ancient astronomy 83 50, 96, 325 Horsehead Nebula 238 micrometers 91
Coathanger 368, 368 history 330–31 Sunyaev–Zel’dovich effect Darwin, Charles 92 naked-eye astronomy 73, 73
cobalt, formation of 95 mapping the sky 332–37 322, 323 databases, computerized parallax shift 66, 66
CoKu Tau (τ) 4 290 zodiac 60, 61 cosmic rays 24, 32, 228 pulsating variable stars 278
cosmological constant 54 telescopes 78 size of Universe 22–23
cosmological red shift 33 days DNA 141
cosmologists 22 Dollond, John 91
cosmology, Earth-centred 85, and length of year 82 Dolphin see Delphinus
85 measuring 62, 62
covalent compounds 29
Crab see Cancer
Crab Nebula (M1, NGC 1952)
94, 266–67, 356, 356
Crane see Grus

index

IGGNUUDIIEDDXEE TTOO TT HH EE UU NN II VV EE RRSS EE Domovoy Crater (Ariel) 199 celestial sphere 58–59 electroweak force 47 Enki Catena (Ganymede) 215 Eta (η) Herculis 348
Doppler effect 33 Earth cont. elements 29 Enlightenment 90 Eta (η) Lupi 383
Dorado (the Goldfish) 405 Ensisheim meteorite 222 Eta (η) Piscium 372
as centre of cosmos 85, 85 formation of 51, 262, 262 Eos Chasma (Mars) 167 Eta (η) Tauri (Alcyone) 273,
Beta (β) Doradus 405 circumference 84, 84 high-mass stars 234 Epimetheus 188, 190
see also Large Magellanic climate 138 planet formation 233 Epsilon (ε) Aurigae (Almaaz) 287, 356
Copernican revolution 86–89 spectroscopy 33, 33 Eta (η) Ursae Majoris (Alkaid)
Cloud eclipses 63 star formation 232 277, 279, 279, 343
R Doradus 405 features formed by water supergiant stars 250 Epsilon (ε) Bootis (Izar) 25, 68, 344
see also Tarantula Nebula (30 Elephant’s Trunk Nebula 241, Eta (η) Ursae Minoris 338
146–47 273, 347, 347, 444 Etamin (Gamma (γ) Draconis)
Doradus) life 52–53, 141, 141 241 Epsilon (ε) Carinae 395
double binary stars 270 lights in the sky 70–71 ellipses, orbits 37, 37, 87 Epsilon (ε) Cepheus 340 339
Double Cluster 354, 354, 480 magnetic field 139, 139 elliptical galaxies 26, 296 Epsilon (ε) Corvi 381 ethane
double-slit test 32 meteorite craters 221, 221, Epsilon (ε) Herculis 348
double stars see binary stars classification 294, 294 Epsilon (ε) Hydrae 378 Jupiter 178
Dove see Columba 222–23 distribution 298 Epsilon (ε) Indi 400 Saturn 187
DR 6 241 meteorites 220 galaxy clusters 316, 317 Epsilon (ε) Lupi 383 “ether” 38
DR 21 244 the Moon 148, 149, 150, 150 M60 307 Epsilon (ε) Lyrae 272, 349 Euanthe 179
Draco (the Dragon) 339, 444, orbit and spin 118, 138, 138 merger model 299, 299 Epsilon (ε) Normae 398 Eudoxus 84, 330
plate tectonics 140, 140 SagDEG 300 Epsilon (ε) Orionis (Alnilam) Euporie 179
450 seasons 61, 61, 138 Eltanin 339 Europa 25, 178, 180–81
Abell 2218 322–23 size 22 Elysium Planitia (Mars) 170 230 possibility of life 53
Cat’s Eye Nebula 254, 339, structure 138, 138 emission nebulae 24, 33, 228, Epsilon (ε) Pegasi (Enif) 370, space probes 110
surface features 141 European Centre for Nuclear
339 tectonic features 140, 142–45 238 462
Etamin (Gamma (γ) Draconis) earthquakes Carina Nebula 245 Epsilon (ε) Sagittarii 384 Research (CERN) 47
Mercury 126 DR 6 241 Epsilon (ε) Sculptoris 388 European Space Agency (ESA)
339 meteorite impacts 221 DR 21 244 Epsilon (ε) Ursae Majoris
Mu (μ) Draconis 339 eclipses 63 Eagle Nebula 242–43 Giotto mission 218
Nu (ν) Draconis 339 eclipsing binary stars 270, 270, IC 1396 241 (Alioth) 68, 344 Hipparcos satellite 66, 66
Omicron (ο) Draconis 339 IC 2944 244 Epsilon (ε) Volantis 406 Rosetta mission 111, 219
Psi (ψ) Draconis 339 354 Lagoon Nebula 241 equator, celestial sphere 58, 59 Eurydome 179
Spindle Galaxy 307 Alpha (α) Herculis (Ras M43 239, 375 equatorial mountings, telescopes evaporating gaseous globules
16 Draconis 339 NGC 604 301, 301
17 Draconis 339 Algethi) 281 NGC 2359 260 76, 76 (EGGs) 236, 242
39 Draconis 339 Eta (η) Geminorum (Propus) Omega Nebula 90, 238, 384, equatorial sky charts 334–37 event horizon, black holes 41,
40 Draconis 339 equinoxes 61, 61, 138
41 Draconis 339 280 385 263
Dragon see Draco Lambda (λ) Tauri 280 Orion Nebula 239 ancient astronomy 83 Everest, Mount (Earth) 144,
Dragon Storm (Saturn) 188 ecliptic 60, 61, 138 RCW 49 245 Pisces 372
Drake, Frank 53 Eddington, Sir Arthur 92, 92, Trifid Nebula 244 precession 355 144
Draper, Henry 239 emission spectrum 33, 33, 231 sky guide 426 evolution
Dresden Codex 83 247 planetary nebulae 251 Equuleus (the Foal) 369
Dreyer, J.L.E. 237 Egg Nebula (CRL 2688) 254 Wolf–Rayet stars 251 Gamma (γ) Equulei 369 galaxies 298–99
Dubhe (Alpha (α) Ursae Egypt Enceladus 188, 189, 192 1 Equulei 369 galaxy clusters 317
Encke, Comet 214, 217 Eratosthenes 84, 84 life 141
Majoris) 68, 344 ancient astronomy 82, 83, 83 Encke, Johann 217 Erichthonius 343 multiple stars 270, 270
Hertzsprung–Russell (H–R) constellations 330 Encke gap, Saturn’s rings 189 Eridanus (the River) 390, 469, star clusters 285
early scientific astronomy 84 Encounter 2001 message 53 stars 233–35
diagram 230 Eight-Burst Nebula (NGC end points, stellar 262–69 481 Ewen, Harold 95
Dumbbell Nebula (M27) 253, Endurance Crater (Mars) see also Achernar (Alpha (α) exotic particles 31, 46
3132) 250–51, 394, 427 expanding space 42–43, 54, 323
368, 368, 456, 457 Einstein, Albert 31, 38, 92, 92 174–75 Eridani) Explorer 1 satellite 99, 139
Dunlop, James 256 Energetic Gamma (γ) Ray Omicron (ο) Eridani 272, extra-solar planets 96, 290–91
Dürer, Albrecht 331 black holes 94 extraterrestrial life 53
dust cosmological constant 54 Experiment Telescope 390, 390 extreme stars 94
energy and mass 39 (EGRET) 35 Theta (θ) Eridani 390 Extreme Ultraviolet Explorer
interstellar medium 24, 228 general theory of relativity energy 32 Eridani 390
storms on Mars 167 atomic bomb 39 40 Eridani B 230 35
zodiacal light 71, 71 40–41, 49 atoms 28 Erie, Lake (Earth) 146 extremophile organisms 53
dusty elliptical galaxies 299, 299 mass and energy 54 Big Bang 46 Erinome 179 eyepieces, telescopes 77, 77
dwarf elliptical galaxies 296, Mercury’s orbit 124 convection 246 Eris 204, 205, 206 eyes, adjusting to dark 72
principle of equivalence 40, dark energy 27, 50, 54–55, 54 Eros 13, 111, 208, 210, 212–13
296, 300 Einstein’s theories 92 mythology 372 F
Canis Major Dwarf 300 40 electromagnetic (EM) erosion
galaxy clusters 316, 316 special theory of relativity radiation 32, 32 Mars 172, 172 F stars 231
SagDEG 300 fate of Universe 54–55 Venus 131 Fabricius, David 281
dwarf stars 38–39 ionization 28 eruptive variable stars 258 faculae, Sun 122
black dwarfs 233, 235, 262 Eistla Regio (Venus) 133 luminosity 231 U Geminorum 280 false colour images,
brown dwarfs 25, 25, 94, 94, El Tajin, Mexico 82 main-sequence stars 246 ESA see European Space Agency
Elara 178 mass 39, 39 Eskimo Nebula (NGC 2392) electromagnetic radiation
232, 291 Electra, in mythology 357 nuclear fission and fusion 31, 35, 35
dwarf planets 204–205 electromagnetic (EM) force 30, 31 358, 358, 255 False Cross 394, 395
photons 32 ESO 97-G13 (Circinus Galaxy) in monthly sky guides 421,
red dwarfs 25, 25, 233 30, 47 protostars 237 427
see also white dwarfs electromagnetic (EM) radiation radiation 246 312 naked-eye astronomy 73
rotation 37 ESO 350-G40 (Cartwheel Family Mountain (Moon) 156
E 32–35 Saturn 187 February sky guide 420–25
“false colour” images 35, 35 stars 230 Galaxy) 309 fermions 31
e Puppis 393 observing 34–35 states of matter 30 ESO 510-G13 308 field equations 41
Eagle see Aquila Sun 120 strong nuclear force 30 Eta Aquarid meteor shower field galaxies 316
Eagle Crater (Mars) 171 electron degeneracy pressure, Sun 120 field of view, binoculars 75
Eagle Nebula (IC 4703) 236, supernovae 262 371, 438, 439 filaments
white dwarfs 262 Enif (Epsilon (ε) Pegasi) 370, Eta (η) Aquarii 371, 439 Big Bang 50
242–43, 364, 364, 451 electrons 28, 28–29 462 Eta (η) Aquilae 282, 367 galaxy superclusters 325, 325
Earth 8, 25, 138–47 Eta (η) Carina Nebula see films, astrophotography 79
Big Bang 47, 48, 48–49 filters 78, 78
age 92 Big Chill 55 Carina Nebula finder scopes 77, 77
asteroids 208 chemical elements 29 Eta (η) Carinae 245, 252, 258, fire altars 83
atmosphere and weather 140, forces 30, 30 fireballs 71, 220
molecules 29 395, 395, 427, 433
140 photoelectric effect 32, 32 Eta (η) Cassiopeiae 341
aurorae 70, 123 plasma 30 Eta (η) Geminorum (Propus)
axis of rotation 60, 60 synchrotron mechanism 310
electroweak era 46–47 280, 358