Science and Environment 10

Fact File - 1

Scientists estimate there are about 1022 stars in the universe.

Fact File - 2

In 1994 AD, Alexander Wolszcan discovered that there were three planets that
revolve around a pulsar.

23.2 Units to Measure the Distance Between Heavenly Bodies

The universe is so vast that the kilometer is an extremely small and inconvenient unit to
express such large distances. The distances between the heavenly bodies like stars and planets
are expressed in terms of the following units:

i. Astronomical unit ii. Light year iii. Par sec

i. One Astronomical Unit (AU): The mean distance between the earth and the sun is called
one astronomical unit. It is equal to 1.5 × 108 km.

1AU = 1.5 × 108 km

= 1.5 × 1011 m.

ii. One light year: The distance traveled by light in one year is called one light year. The
diameter of the solar system is about 10.5 light years.

Let us see how the distance travelled by light is calculated.

We know, speed of light = 3 × 108 m/s

time = 1 year
We have,

Distance traveled by light = speed of light × time

In one year = 3 × 108 m/s × 1 year

= 3 × 108 m/s × 365 days

= 3 × 108 m/s × 365 × 24 hours

= 3 × 108 m/s × 365 × 24 × 60 minutes

= 3 × 108 m/s × 365 × 24 × 60 × 60 seconds

∴ One light year = 9.46 × 1015 m = 9.46 × 1012 km.

It is to be noted that one light year is the unit of distance and not of time.

iii) 1 par sec: The distance having the value 3.26 light years is called 1 par sec.

23.3 Solar System

The solar system consists of the sun, eight planets, their satellites and many other celestial
bodies, like asteroids, comets, meteors, etc. The family of the sun, including all planets and
their satellites, meteors, comets, asteroids, etc., is called the solar system. All the members
of the solar system revolve around the sun, in the same direction, in elliptical orbits. This
revolution is possible due to the gravitational pull of the sun on all the planets and other
bodies.

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Fig. 23.2 Solar system

23.4 Sun

The sun is the main source of all the energy of the solar system.

The sun is located in the middle of the solar system. The mass of

the sun is about 740 times more than the total mass of the planets

of the solar system. It is a medium sized yellow star. The size of

the sun seems to be bigger than the size of other stars because the

earth is comparatively nearer to the sun. The average diameter

of the sun is about 1392400 km. The average temperature of the Fig. 23.3 Sun
sun is 10,0000F and the temperature of its core is about 35 crore0F.

The sun is about 1299370 times bigger than the earth by volume and it is 332946 times bigger

by mass. The relative density of the sun is about 1.41. The sun is about 1.5x108km (1AU) away

from the earth which, is 1 astronomical unit distance away. The solar radiation is coming out

from its surface due to thermonuclear fusion reaction. The sun emits solar radiation which

contains infra red ray, UV ray, X-ray, radio wave and other electromagnetic radiation. It emits

solar wind; it is the stream of charged gaseous ions emitting from the surface of the sun. It has

a speed of 500km/s. The sun is not a solid body. It is a sphere of hot gases. It consists mostly of

hydrogen gas. In the center of the sun, hydrogen atoms are continuously combining to form

helium atoms. Please note that some mass is lost during the nuclear fusion reaction, which

gets converted into energy according to Einstein’s mass-energy relation (E = mc2). The age of

the sun depends on the amount of hydrogen present in its core.

Fact File - 3

The speed of the solar wind is about 500 km/s.

Importance of the sun

The sun is an important heavenly body for living organisms of the earth as well as the existence
of the heavenly bodies in a particular position of the space due to gravitational force. The
sun helps in the photosynthesis of green plants. It provides the necessary temperature to the
earth’s surface for the existence of living organisms. Solar (photo) cells can be operated with
the help of solar energy. The sun provides the necessary gravitational force to the planets and
other heavenly bodies.

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23.5 Planets

Planets are heavenly bodies which revolve around the sun in elliptical orbits. They do not
have their own source of light. A planet shines because it reflects the light from the sun. The
planets are much nearer than the stars so they appear to be big and do not twinkle at night.
The planets are very small as compared to the sun or other stars. There are eight planets in the
solar system, including the Earth.

The eight planets of the solar system are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus
and Neptune. Pluto was considered as the ninth planet of the solar system till 2006. But, it has
been removed from the list of planets and taken as a dwarf planet according to the decision of
the International Astronomical Union because of the following reasons:

i. The size of Pluto is very small as compared to the average size of other planets.
ii. The orbit of Pluto coincides with the orbit of Neptune.
iii. The orbit of Pluto does not lie on the same plane to the plane of orbits of other

planets.

Scientists have predicted the presence of some extra solar planets outside the solar family. An
American astrologer, Alexander Wolazcan, announced that there were three planets in one
pulsar star. A fast moving star radiating radio frequency is called pulsar.

The earth sometimes comes nearer to the sun and sometimes it goes far. Because planets
revolve a round the sun in elliptical orbits, their position changes continuously. Due to this,
they were named planet. In Greek language, planet means ‘wanderer’. The shape, size and
materials by which planets are formed are different. Smaller planets are nearer to the sun
while the bigger and medium sized planets are far from the sun. Depending on the position of
the asteroid belt, planets are classified as inner planets and outer planets.

1. Inner planets: Those planets which are present inside the asteroid belt are called inner
planets. They are Mercury, Venus, Mars and Earth. These planets have a similar structure
as that of the earth. So they are also called terrestrial planets. The terrestrial planets have
the following common features:
i. They have a thin rocky crust.
ii. They have a mantle rich in iron and magnesium.
iii. They have a core of molten metals.
iv. They have very few moons or no moons or natural satellites.

2. Outer planets: Those planets which are located outside the asteroid belt are called outer
planets. Jupiter, Saturn, Uranus and Neptune are called the outer planets because they
are big in size and the structure is similar to that of Jupiter. They are also called Jovian
planets. The Jovian planets have the following common features:
i. They are made up of gases. ii. They have a ring structure around them.
iii. They have a large number of moons or natural satellites.

astrologer /əˈstrɒlədʒer/ - a person who studies the positions of stars and the movement of planets in the belief that they

influence human affairs
pulsar /ˈpʌlsɑː/ - a star that cannot be seen but that sends out regular rapid radio signals

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396 Oasis School Science - 10 Table 25.1 Comparative study of planets of the solar system

Planet Avg. Least dis- Period Avg. Diameter Period of Surface Gravity Gases in the atmp- Mass Density Density No. of
Distance tance from of rev- Orbital (km) rotation temperature (earth =1) sphere (possible) (earth=1) (gm/cc) (earth=1) satellites
from the earth olution velocity known
the sun (x106km) (days/or (km/s) (0F) 5.42 1
(x107km) years) 5.25 0.97 0
5.52 1 0
Mercury 5.76 891.7 87.97 47.89 4851.2 58.65 days 333 0.386 Not present 0.055 3.99 0.73 1
day 1.33 0.25 2
0.69 0.13
Venus 10.72 41.4 224.7 35.63 12035.2 243.02 days 465 0.871 CO2, H2O, O2 0.815 1.27 0.23 63
days 1.64 0.30
Geology and Astronomy 60
Earth 14.88 - 365.25 29.79 12672 23 h 56 m 45 1 N2, O2, CO2, H2O 1 27
days 13

Mars 22.56 55.7 686.98 24.13 6742.4 24 h 37 m -80 0.38 CO2, N2, Ar, O2, 0.107
days 22s CO, Ne, Kr, Xe, H2O

Jupiter 76.8 628.76 12 13.06 1139040 9 h 55 m -160 2.53 H2, He, CH4, NH3, H2O 317.892

years

30 s

Saturn 144 1277.4 29.5 9.64 115811.2 10 h 30m -220 1.07 H2, He, CH4, NH3 95.16

years

Uranus 288 2587 84 6.81 50441.6 17 h 14m -323 0.91 H2, He, CH4, NH3, H2O 14.54

years 24 s

Neptune 448 4310 164 5.43 48972.8 16 h 6m 36s -330 1.14 CH4 17.15

years

Source: World Almanac, 2007

23.6 Brief Description of the Planets of the Solar System

1. Mercury

Mercury is the smallest planet of the solar system. It is the

nearest planet to the sun. It is very hot during the day time

since it is closest to the sun. It has no atmosphere and water.

So, this planet cannot support life. Due to its less distance

from the sun, it revolves faster than the other planets. It has

a similar surface as that of the moon due to the formation

of craters. The phases as on the moon can be observed on

the surface of Mercury when viewed through a telescope. Fig. 23.4 Mercury

Mercury completes one rotation in 59 days and one revolution

around the sun in 88 days. This planet has no moon. Many craters have been formed in

this planet due to meteor shower.

Fact File - 4

The temperature of Mercury 1700C to 4270C.

2. Venus

The second planet from the sun is Venus. It is the closest

planet from the earth. This planet is the brightest object in the

night sky (except the moon). In the early morning, it is visible

in the eastern sky, and it is visible in the western sky in the

evening. Due to its nearness to the sun, it is too hot to support

life. Venus has no water. It is slightly smaller than the earth.

Its high level of carbon dioxide causes a greenhouse effect. Fig. 23.5 Venus

Excessive heating of Venus due to this makes it the hottest

planet. So, the surface temperature of Venus is very high. It is visible in crescent form

when it comes near the earth. But it appears the brightest due to the nearest distance.

Fact File - 5

The diameter of Venus is about 12035 km. Its average temperature is about
4800C.

Reasonable Fact-1

Life is not possible in venus though it contains water, oxygen and carbon dioxide,
give reason.

Ans: The surface temperature of venus is very high, i.e., about 8650F, or 462.770C
which is not suitable for the survival of living beings. Therefore, life is not possible
in Venus though it contains water, oxygen and carbon dioxide.

crater /ˈkreɪtə/ - a large hole in the ground caused by something large hitting it

crescent /ˈkrez(ə)nt/ - a curved shape that is wide in the middle and pointed at each end

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3. Earth

The third planet from the sun is the earth. It is the fifth biggest
planet in the solar system. It appears blue when viewed from
outer space. It is due to the reflection of light from the water
body from the earth. Earth is the only planet which supports
the existence of life. The existence of living organisms is due
to the following reasons:

i) Earth has a suitable temperature for the survival of life. Fig. 23.6 Earth
ii) Earth has sufficient amount of water.

iii) Earth has oxygen, carbon dioxide and nitrogen in its atmosphere.

iv) It has a protective layer of ozone gas, which protects living organisms from the
ultra-violet radiation coming from the sun.

4. Mars

The fourth planet from the sun is mars. It has an atmosphere

containing traces of carbon dioxide, hydrogen, oxygen and

nitrogen. The oxygen in the mars is too little for the survival

of living organisms. It is popular as the red planet due to the

presence of limonite (iron oxide) rock on it. Mars does not

have water on its surface, so it cannot support life on it. It

has a more elliptical orbit than that of the earth. Big craters Fig. 23.7 Mars

and volcanoes are seen in mars. Black spots are also seen one-

third of mars. Two white polar caps made of the ice of gases are present on two sides of the

mars. The shape of those caps decreases when they face the sun as ice melts. Mars has two

natural satellites, which are: Phobos and Deimos.

Reasonable Fact-2

Why is the mars called the red planet?

Ans: Mars appears red due to the presence of a mineral rock, i.e. limonite. So, the
mars is called the red planet.

5. Jupiter Fig. 23.8 Jupiter

Jupiter is the largest planet of the solar system. It is the fifth
planet from the sun. It is made up of hydrogen, helium,
methane and ammonia. It is seen as a colorful object when
seen through a telescope. Jupiter has thin rings around it. It is
believed that cloud is formed due to the freezing of methane
and carbon dioxide. Jupiter has a great red spot in its
atmosphere. It is believed that this is due to atmospheric
hurricane. The length of the red spot is about 40,000 km and its
breadth is about 32000 km. It is not visible due to the dense

hurricane /ˈhʌrɪk(ə)n/ - a violent storm with very strong winds

398 Oasis School Science - 10 Geology and Astronomy

cloud on its surface. In 1994 AD, a comet called Shoemaker Levy broke into several pieces
when it struck the Jupiter. Jupiter has 63 known planets. Among them, Ganymede is the
largest.

6. Saturn Fig. 23.9 Saturn

The sixth planet from the sun is Saturn. It is the second
biggest planet in the solar system. As jupiter, saturn also
has hydrogen and helium. It is surrounded by three
elliptical rings made of fragments of ice. This is the unique
feature of Saturn. This planet has minimum density among all
planets. This planet has 60 known satellites. Titan is the largest
satellite of this planet. The diameter of Titan is about 5140 km.
It has its own atmosphere which consists of nitrogen.

7. Uranus Fig. 23.10 Uranus
Fig. 23.11 Neptune
It is the seventh planet from the sun. It is the first planet
which was discovered by using a telescope. It is the third
biggest planet of the solar system. It is also made up of
clouds of minute crystals of methane, hydrogen and helium
gas. This planet rotates from the east to the west in its axis. It
is believed that water lies beneath the level of ammonia, and
a rocky core is present in its center.

8. Neptune

Neptune is the farthest planet of the solar system. It is the
eighth planet of the solar system. It has a ring-like structure
around it. It is an extremely cold planet. Its surface contains
hydrogen, helium, neon, silicate and water. It has a great
dark spot having the size as that of the earth. Its has a rocky
core made of liquid gas. It has 13 known satellites. Triton is
the biggest satellite among them. It has a diameter of about
2705 km. This satellite revolves around Neptune from a
distance of 33500km.

Reasonable Fact-3

Why is Pluto not considered as a planet of the solar system? Give three reasons.
Ans: Pluto is not considered as a planet of the solar system because:

(i) The size of Pluto is very small as compared to the average size of other planets.
(ii) The orbit of Pluto is coincides with the orbit of Neptune.
(iii) The orbit of Pluto does not lie in the same plane as the orbits of other planets.

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23.7 Satellite

A satellite is a heavenly body which revolves round a planet on its own orbit. There are two
types of satellites: natural satellite and artificial satellite.

1. Natural satellite

A satellite which is made by nature that revolves continuously around a planet is called
a natural satellite. Natural satellites of some planets are given below:

Planets Natural satellites No. of satellites discovered so far

Earth Moon 1
Mars Deimos, Phobos 2
Jupiter Gyanymede, Callisto 67
Saturn Titan, Rhea 62
Uranus Titenia, Ariel 27
Neptune Triton, Nereid 14

Fact File - 6

Mercury and Venus have no satellites.

23.8 Moon

Moon is the natural satellite of the earth. The diameter of the moon

is about 3456 km. The mean distance between the earth and the

moon is about 382400 km. Gravitational force of the earth holds

the moon in its orbit. The moon has no air and water. Its surface

is covered with hard and loose dust, craters and mountains. Days

are extremely hot and nights are very cold on the moon. The moon

appears to be much bigger than the stars as it is nearer the earth.

Actually, the moon is much smaller than the stars and planets. The

moon reflects the light of the sun but it has no light of its own. The Fig. 23.12 Moon

moon completes its revolution around the earth in 27 1 days. This
3
time period is called the sidereal month. The time period between one full moon (or new
gmroaovnit)yaonfdthaenomthooernfiuslal bmoouotn61(othronfetwhamt oofotnh)eiseacratlhle. dThtheeresylantiovdeicdmenosnittyho. Iftthhaesm2o9o21n
days. The
is 3.3.

Differences between Synodic month and Sidereal month

S.N. Synodic month S.N. Sidereal month

1. The time period between any two 1. The time required for one complete
consecutive full moons or new revolution around the earth by the
moons is called the synodic month. moon is called the sidereal month.

2. It has 29 1 days. 2. It has 27 1 days.
2 3

cosmic /ˈkɒzmɪk/ - connected with the whole universe

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2. Artificial satellite

Those satellites which are made by humans and launched in space are called artificial
satellites. For example, Sputnik, INSAT, METSAT, etc. They revolve around the planet from
a fixed distance. There are many artificial satellites sent to the space which revolve a round
the earth. Russians were the first to launch the artificial satellite Sputnik I on October 4th,
1957.

Purposes of launching artificial satellites Fig. 23.13 Sputnik

1. For the communication of radio, TV and
telephone signals across the world

2. For weather forecasting

3. To study space and different regions of
the earth

4. For the study of cosmic rays and solar
radiation

5. For surveying natural resources
6. For spying or military purposes

23.9 Asteroids

The rock and metal objects which are present in Fig. 23.14 Asteroid belt
between the orbits of Mars and Jupiter that revolve
around the sun are called asteroids or minor planets.
There may be as many as 100000 asteroids in the
solar system. The biggest asteroid is Ceres which
has a diameter of about 800 km whereas the smallest
asteroid is as small as a pebble. Examples of other
asteroids are Juno, Vesta, Pallus, Eros, etc.

Differences between Planets and Asteroids

S.N. Planets S.N. Asteroids

1. Those heavenly bodies which revolve 1. Those heavenly bodies which revolve

around the sun are called planets. around the sun mainly in between Mars

and Jupiter are called asteroids.

2. They are bigger than asteroids. 2. They are smaller than planets.

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23.10 Comets

When we observe the sky at night, we can see a tailed structure revolving around the sun. A
broom shaped shining object with a bright head is called a comet. It is made of gases, dust
and ice. The head is made up of ice. The head of the comet is called coma and the central
part of the coma is called the nucleus of the comet. Sometimes the normal path of the comet
is disturbed by the star, and it starts moving towards the sun. As the comet approaches the
sun, it develops a long glowing tail and becomes visible to us. A comet becomes visible only
when it approaches the sun as the ice and gaseous particles get evaporated due to heating
of the sun. The thus formed gas and particles of ice flow to the opposite direction of the sun
due to the solar wind and form a long tail. The rays of the sun make its gas glow, which
spread, out to form a tail millions of kilometers long. Comets have no light of their own.
They reflect the light from the sun.

Comets revolve around the sun in long elliptical orbits. Different comets have different
periods of revolution. Halley’s Comet is seen after every 76 years. It was last seen in 1986
AD. This comet was studied in detail by a scientist named Edmund Halley. So, it was named
after his name.

The comet's tail develops
as it gets closer to the sun

Sun Comet
A comet spends
most of its time in the
outer solar system

Fig. 23.15 Comet revolving around the sun

S.N. Name of Comets First Observed Revolution (years)
1 Halley’s Comet 240 BC 76
2 Temple- tutle 1366 AD 33
3 Enke 1786 AD 33
4 Schwasman- Washman 1927 AD 15
5 Bennet 1969 AD 1678
6 Shoemaker Levy 1992 AD unknown

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When the comets approach the sun, they lose some ice, gas and dust each time. Ultimately
they convert into small fragments like asteroids. Some of the fragments enter the earth's
atmosphere and with other heavenly bodies and get crumbled into pieces. As a result, some
comets disappear forever.

Reasonable Fact-4

Why does a comet develop a tail when it comes nearer to the sun?
Ans: When a comet approaches the sun, some of its frozen matter begins to evaporate into
gases due to the heat of the sun. These gases rush out by rapid vaporization in the form of
jets, carrying solid particles with them. In this way, a long tail of a comet is formed due to
the motion of the comet and effect of the solar wind.

Reasonable Fact-5

A comet loses its tail when it is far from the sun. Why?
Ans: The tail of a comet is made up of ice and dust particles. When the comet comes closer
to the sun, the ice vapourizes and a long tail appears due to the high speed of the comet
and effect of the solar wind. But when the comet moves away from the sun, the ice does
not vapourize due to low temperature and finally disappears.

Reasonable Fact-6

A comet is seen only after a long period, why?
Ans: Comets are seen in the sky when they approach the sun. Comets take many years
to complete one revolution around the sun. For example: Halley's comet completes one
revolution around the sun after 76 years. So a comet is seen only after a long period due
to its very long elliptical orbit.

Reasonable Fact-7

Why does a comet break into pieces on coming close to the planet Jupiter?
Ans: When a comet comes close to the Jupiter, the parts of the comet that are nearer to the
Jupiter experience much greater gravitational pull of the Jupiter than other parts of the
comet. This large difference in the gravitational pull of the Jupiter, on different parts of the
comet, breaks the comet into pieces. For example, in 1994, the comet called "Shoemaker
Levy' broke into many pieces when it came too closer to Jupiter.

23.11 Meteors (Falling stars or Shooting stars)

The pieces of stone or metal which enter the earth’s atmosphere are called meteors. These are
streaks of light in the sky at night, which disappear within a few seconds. Some meteors are
formed from the dust particles left behind by the comets, and others are pieces of asteroids
which have collided. When the heavenly body enters the earth’s atmosphere with high speed,
friction is developed between the body and air. Due to the friction, heat is produced in it, and a
burning object is seen in the atmosphere in the form of a streak of light. A meteor lasts for a very
short time because the small rock pieces burn and vaporize completely due to the excessive

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heat produced by atmospheric friction. Sometimes the Fig. 23.16 Meteor shower
big meteors do not burn completely and may reach the
surface of the earth. This object is called a meteorite. A
large number of meteors fall near the North Pole and
South Pole of the earth. A meteor shower can be seen in
the polar regions. An extremely large and bright meteor
shower is called fire ball. Depending on the composition
of the material, the meteorites can be classified into the
following three groups:

i. Stony meteorites: They are meteorites having more amount of silicon than iron and
magnesium.

ii. Iron meteorites: They are meteorites having more amount of iron and negligible amount
of silicon.

iii. Stony iron meteorites: They are meteorites having almost equal amounts of silicon and
iron.

Reasonable Fact-8

A meteor is finished before reaching the earth's surface. Why?
Ans: A burning stone resembling a falling star is called a meteor. When a meteor
comes towards the earth's surface at a great speed, it burns completely due to the
friction between the meteor and atmospheric gases. Therefore, a meteor is finished
before reaching the earth's surface.

About fifty thousand years ago, a meteorite fell in Arizona of
USA, and a deep crater was formed, which is shown in the
given figure. The crater was 1275 m wide and 175 m deep.
This can be seen nowadays. Here, the main stone entered
deep into the earth’s surface, but many broken pieces were
scattered around the crater. It is, said that meteors start to burn
at a height of 7km to 120 km. They have a speed of 70 km per
second. The meteorites found on a earth are mostly iron type. Fig. 23.17 Crater in Arizona, USA

The mass of meteorites found so far ranges from 100 grams to

20000 kilograms.

Differences between Comets and Meteors

S.N. Comets S.N. Meteors
1.
Broom-shaped shining objects with a 1. The pieces of stone or metal which
2. bright head made up of ice are called enter the earth’s atmosphere are called
comets. meteors.

They have a long glowing tail-like 2. They have streaks of light falling
structure. down towards the earth surface.

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23.12 Galaxy

Space contains billions of stars. They have different clusters or groups. This cluster of stars is
called a galaxy. Thus, a galaxy is a vast system of stars, dust particles and gases isolated from
a similar system in space. These stars in the galaxy revolve around a common center called the
galactic center. There are about 1011 galaxies in the universe. The diameter of a galaxy is about
1000 light years to 10 lakh light years. Our solar system is present in the Milky-way galaxy.

Types of Galaxies

On the basis of shape, there are three types of galaxies. They are:

a. Spiral galaxies: Galaxies which are spiral in
shape are called spiral galaxies. Examples:
Milky-way galaxy, Andromeda galaxy, etc.
Our solar system is located in one corner of the
Milky-way galaxy. This galaxy consists of 1011
stars. This galaxy has a disk-like structure at its
middle which tapers towards its sides. A dusty
cloud is found between the stars of this galaxy.

Fig. 23.18 Spiral galaxy (Milkway galaxy)

The mass of Milky-way galaxy is about 1.33 × 1011
times more than that of the sun.

b. Elliptical galaxies: The galaxies which are oval in shape are called elliptical-shaped
galaxies. These galaxies contain a little amount of interstellar matter. The stars found in
these galaxies are very old. Their peripheral part is dim and the central part emits bright
light.

Fig. 23.19 Elliptical galaxy Fig. 23.20 Irregular galaxy

c. Irregular galaxies: Galaxies that do not have a regular shape are called irregular galaxies.
They have bright stars at the central part. These galaxies are less brighter than elliptical
galaxies.

The distance between the galaxies can be found with the help of electromagnetic radiation
coming from them. Scientists say that the galaxies are moving apart at a very high speed.
This signifies that space is expanding.

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23.13 Big Bang Theory Fig. 23.21 Big Bang Explosion

According to this theory, all the matter in the universe was
originally concentrated in one vast lump called a primeval
atom. About 15 billions years ago, this super dense and
extremely hot body having neutrons and protons exploded
with a big bang, and the matter started flying in all directions
through space, leading to the formation of galaxies of the stars
and other heavenly bodies. Now, we are nearly 15 billion
years after the Big-Bang explosion, and it is believed that the
universe is expanding continuously and will continue in the
future as well.

23.14 Constellation

We have seen thousands of stars in a clear night sky. Some of them are in a group or pattern. The
group of stars in the sky which resemble an animal or any other shape is called a constellation.
Our ancestors named those stars or constellation after the object which they seemed to resemble.
Till now 88 constellations are known. That means 88 groups of stars have got names. Each
constellation has been given a name signifying an animal, a human being or some other objects
to which it appears to resemble. Some of the famous constellations are:

1. Ursa Major 2. Ursa Minor 3. Aries
4. Orion 5. Taurus 6. Gemini
7. Cancer 8. Leo 9. Virgo
10. Libra 11. Scorpio 12. Sagittarius
13. Capricorn 14. Pisces 15. Aquarius
16. Draco 17. Cepheus 18. Cassiopeia
19. Perseus 20. Musca 21. Tucana

Cassiopeia Ursa Major Ursa Minor Cepheus

Fig. 23.22 Some constellations

From 1400 AD to 1700 AD, sailors gave names of scientific material, animal, etc. to the
constellations seen on their ways to the southern hemisphere, e.g., Tucana, Musca, Telescopian,
etc. The constellations seen in a particular season are not visible in another season due to the
revolution of the earth around the sun. We can see different constellations from the north and
south hemisphere of the earth.

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23.15 Some Famous Constellations

1. Ursa Major Fig 23.23 Ursa major

Ursa major is a common and easily recognizable or
detectable constellation. It has seven big stars appearing
like the shape of a question mark. This group of stars
is called big dipper or Great Bear. In Hindu mythology,
Big Dipper is called ‘Saptarishi’. The Saptarishi includes
Dubhe, Merak, Phecda, Megrez, Alioth, Mizar and Alkaid. It
appears in the summer season in the northern sky.

2. Ursa Minor

This constellation is also known as the Little Bear. It is a group of seven stars that seem
to form the shape of a dipper or ladle. Out of the seven stars, four stars form the ‘bowl’
of the Little Dipper and three stars form the handle of the ladle. This constellation can be
seen in the northern hemisphere. The stars of this constellation are less bright and nearer
than those in the Big Dipper.

Fig 23.24 Ursa Minor

3. Orion

Orion consists of a large number of stars arranged in the shape of a
hunter. It is named after the name of a hunter in Greek mythology.
The stars present in it are Betelgeuse, Rigel, Saif, Mintaka, Alnilam,
etc. It appears in the winter season in the northern hemisphere.

Fig 23.25 Orion

23.16 Superstitions Regarding Zodiacs

The twelve special constellations of the solar path are called zodiacs. Out of 88 constellations, 12
constellations appear to move on the solar path throughout the year. Some other constellation
fall on the solar path, but only 12 of them are considered as zodiacs. These twelve zodiacs are
as follows:

1. Aries 2. Taurus 3. Gemini 4. Cancer

5. Leo 6. Virgo 7. Libra 8. Scorpius

9. Sagittarius 10. Capricorn 11. Aquarius 12. Pisces

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Aries Taurus Gemini Cancer

Leo Vigro Libra Scorpius

Sagittarius Capricorn Aquarius Pisces

Fig. 23.26

Some superstitions regarding zodiacs are mentioned below:

1. Astrologers match the zodiacs and stars of the bride and groom before marriage. However,
there are many examples of unsuccessful marriages seen as good by astrologers.

2. There is no scientific evidence about travel and starting work according to the zodiac,
name and days.

3. Astrologers believe that the nature and behavior of a person differ according to his/her
zodiac. But there is no scientific evidence.

4. In our society, people wear stones and rings according to their zodiac, thinking that these
stones and rings protect them from bad things. However, there is no scientific evidence.

5. There are only 12 zodiacs and millions of people. So one cannot forecast the future of
these people on the basis of their zodiac.

6. Some persons tease people connecting them with their zodiac. But the nature of all
persons having the same zodiac is not the same.

7. In our society, a person born on a new moon is married only with a person born on a new
moon, stating that it is dangerous to marry any other person. But, there is no scientific
evidence regarding this fact.

There is no scientific proof regarding the above mentioned facts. So we should not believe
and follow these superstitions.

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Importance of zodiacs

People study the zodiacs, and they find out the time at night, forecast the weather and identify
other stars. Similarly, navigators find their way in the sea on the basis of the location of different
zodiacs. Therefore, zodiacs are very important for human beings.

Differences between Galaxy and Constellation

S.N. Galaxy S.N. Constellation

1. It is a collection of billions of stars. 1. It is a collections of limited number of
stars.

2. It has no regular pattern. 2. It has a regular pattern.

3. There are about 1011 galaxies in the 3. There are 88 constellations named so far.
universe.

23.17 Stars

The heavenly bodies which have their own source of light are called stars. Stars have their
own source of light because of the thermonuclear fusion reaction. A star is a huge mass of hot
gases and big flames. Stars are made up of vast clouds of hydrogen, helium and dust particles.
There are billions of stars in the sky, but we can see about 2000 stars with the naked eye on
a clear moonless night. All the stars are very big in size but appear small as they are very far
from us. The sun is also a medium sized star. Some stars are bigger than the sun, but some are
even smaller than the earth. The colour of a star changes in the order of VIBGYOR.

Violet → Indigo → Blue → Green → Yellow → Orange → Red

The temperature of a blue star is more than that of a red star. The temperature of a blue star is
about 24000°C, and a yellow star has temperature of 5500°C. The rate of change of size of a star

depends on the energy produced by the thermonuclear fusion reaction and the mass of the star.

Differences between Meteors and Stars Stars mainly
They are made of gases
S.N. Meteors S.N. hydrogen and helium.
1. They are made up of stone, iron 1. They are luminous bodies.

or both.
2. They are non-luminous bodies. 2.

Differences between Planets and Stars

S.N. Planets S.N. Stars

1. Those heavenly bodies which revolve 1. Those heavenly bodies which do not

around the sun are called planets. revolve around the sun are called stars.

2. They are non-luminous objects. 2. They are luminous objects.

3. They do not twinkle at night. 3. They twinkle at night.

4. They have comparatively very low 4. They have comparatively very high

temperature. temperature.

5. They are small in size. 5. They are big in size.

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SUMMARY

• The universe is all of space-time and everything that exists therein
including all planets, satellites, stars, galaxies, constellations, comets, dust
particles, matter, energy, etc.

• Our solar system is located in the Milky-way galaxy. This galaxy consists
of more than one billion stars.

• The mass of the sun is about 740 times more than the total mass of the
planets of the solar system. It is a medium-sized yellow star.

• Planets are heavenly bodies which revolve around the sun in elliptical
orbits.

• There are eight planets in the solar system, including the Earth.

• Those planets which are present inside the asteroid belt are called inner
planets. They are Mercury, Venus, Mars and Earth.

• Those planets which are located outside the asteroid belt are called outer
planets.

• The moon appears to be much bigger than the stars as the moon is nearer
to the earth. Actually, the moon is much smaller than the stars and planets.

• Those satellites which are made by humans and launched in space are
called artificial satellites.

• The rock and metal objects which are present in between the orbits of the
Mars and Jupiter that revolve round the sun are called asteroids or minor
planets.

• A broom shaped shining object with a bright head is called a comet.

• The pieces of stone or metal which enter the earth’s atmosphere are called
meteors.

• A meteor lasts for a very short time because the small rock pieces burn and
vaporize completely due to the excessive heat produced by atmospheric
friction.

• An extremely large and bright meteor shower is called a fire ball.

• A group of stars in the sky which resemble the animal, god or materials is
called a constellation.

• The heavenly bodies which have their own source of light are called stars.

• Stars are made up of vast clouds of hydrogen, helium and dust particles.

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Exercise

Group-A

1. What is the universe? Write down its width.

2. What is solar system?

3. Name the galaxy in which our solar system is located.

4. What is 'light year'?

5. What is Astronomical Unit?

6. What is the diameter of the solar family?

7. Name any one natural satellite of the given planets.

i) Saturn ii) Jupiter

8. Name any one natural satellite of the given planets.

i) Mars ii) Neptune

9. Define satellite.

10. Write any two features of the moon.

11. Name the following celestial bodies:

i) Planet without natural satellite

ii) Farthest planet from the sun

12. Name the following celestial bodies:

i) Planet having polar caps

ii) Planet having big black spot

13. Name the following celestial bodies:

i) Nearest planet from the sun ii) Red planet having limonite rocks

14. What is a comet?

15. What is a meteor?

16. What is a meteorite?

17. What is galaxy?

18. How many types of galaxies are there? Name them.

19. What is a constellation?

20. Write the name of largest satellite of Saturn and name the gas abundantly found in its
atmosphere.

21. What is constellation?

22. Give two examples of constellation.

23. What is solar wind?

24. What is fire ball?

25. Name a constellation which can be seen with naked eyes.

26. Write name of two asteroids.

27. What is the distance on one light year?

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28. Write down the names:
i) Nearest planet from the sun ii) Largest satellite of the Saturn
50. Name the planet nearest to the sun and the planet nearest to the earth.

Group-B

1. Write any two differences between outer planets and inner planets.

2. Write any two differences between planet and satellite.

3. Write any two differences between galaxy and constellation.

4. Write any two differences between star and comet.

5. Write any two differences between sidereal month and synodic month.

6. Pluto is considered as a dwarf planet, why?

7. A meteor disappears before reaching the earth's surface, why?

8. A comet is not actually a star, why?

9. A comet appears only after a long period, why?

10. A tail develops in a comet when it approaches the sun, why?

11. Give reasons:

i) The surface temperature of the mercury reaches very high (about 420 0C).

ii) It takes about 248 years for the pluto to revolve round the sun.

12. Differentiate between constellation and zodiac.

13. Write any two differences between natural satellite and artificial satellite.

14. Write any two differences between light year and astronomical unit.

15. Mars is called a planet and the sun is called a star, why?

16. Some comets disappear forever. Give two reasons.

17. The comet is not a star, why?

18. Give the reasons of disappearing of meteors in the atmosphere.

19. A comet is not actually a star. Give two evidences in favour of this statement.

20. A comet loses its tail when it is far from the sun,

21. A meteor is finished before reaching the earth's surface, why?

Group-D

1. Write down the position of the sun in the universe and mention any three features of the sun.

2. Write short notes on:

i) Mercury ii) Jupiter

3. Write a short note on Milky way galaxy.

4. How are constellation named?

5. Write what can be estimated about the mean surface temperature of the planets as their
distance increases from the sun.

6. What do you know about big-bang theory? Describe in brief.

7. Introduce zodiacs and explain any two zodiacs with figure.

8. Write down importance of observation of constellation in our daily life.

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Compulsory Science

SEE Specification Grid-2074

Area Unit (K) (U) (A) (HA) Total Remarks
1. Physics 5×1 4×2 2×3
2. Chemistry 1. Force 1×4 23
4×1 4×2 2×3
3. Biology 2. Pressure 1×4 22
5×1 4×2 2×3
4. Geology and 3. Energy 1×4 23
Astronomy 1×1 1×2 -
4. Heat 15 13 6 1×4 7
15 26 18
5. Light 4 38
16 75
6. Current Electricity &
Magnetism

7. Classification of
Elements

8. Chemical Reaction

9. Acid, Base and Salt

10. Some Gases

11. Metals

12. Hydrocarbon and its
Compounds

13. Materials Used in
Daily Life

14. Invetebrate Animals

15. Human Nervous and
Glandular System

16. Blood Circulatory
System in Human Body

17. Chromosome and
Sex Determination

18. Asexual and Sexual
Reproduction and
Artificial Vegetative
Propagation in Plants

19. Heredity

20. Environmental
Pollution and
Management

21. History of the Earth

22. Climate Change and
Atmosphere

23. The Earth in the
Universe

Total

Grand Total

Geology and Astronomy Oasis School Science - 10 413

SECONDARY EDUCATION EXAMINATION (SEE)

Compulsory Science

New Model Question (Issued by CDC, 2074)

Time: 2 hrs. 15 min. Full Marks: 75

Note: All the questions are compulsory.

Group-A 15 × 1 = 15

1. Write short answer to the following questions.

a. Define Universal Gravitational Constant ‘G’.

b. State Pascal’s law.

c. What are the types of energy sources based on time of replacement? Write their

names.

d. What is short-sightedness?

e. Define 1 unit of electricity.

f. State the Modern Periodic Law.

g. What is meant by combination reaction?

h. Name any one base with its molecular formula.

i. Write two ores of aluminium metal.

j. Name two types of silkworms cultivated in Nepal.

k. What is hormone?

l. What is chromosomal disorder?

m. Name any two organisms which are reproduced by multiple fission.

n. What is mutation?

o. Define ozone layer.

Group-B 13 × 2 = 26

2. Study the given diagram and answer the following

questions.

i. What is the weight of weighted object in air?

ii. How much upthrust is exerted by the liquid on that

object?

iii. Calculate the mass of the object.

3. Write any two points to justify that the urbanization brings energy crisis.

4. Deserts are very hot during the day and very cold during the night. Give reason.

5. Which type of transformer is given in the figure? Which
substance is used to laminate its core? The number of turns
of primary coil and the number of turns of secondary coil in
a transformer are never made equal, why?

414 Oasis School Science - 10 Geology and Astronomy

6. What is the cause for placing calcium in IIA group of the modern periodic table?

7. How does heat enhance the rate of chemical reaction? Explain in short.

8. How is saturated hydrocarbon differed from unsaturated hydrocarbon? Write any two
differences..

9. Excessive uses of chemical fertilizers causes chemical pollution. How?

10. Honeybee is very important insect for human beings and plants. Write any two reasons.

11. Write any two differences between cerebrum and cerebellum.

12. What preventive measures should be adopted for the disease diabetes?

13. Why is vegetative propagation beneficial to the farmers? Justify it with two reasons.

14. Why does the tail of comet appear when it approaches near the sun? Explain in short.

Group-C 6 × 3 = 18

15. If the mass of the moon is 7.2 × 1022 kg and radius is 1.7 × 106 m, what will be the acceleration

due to gravity of the moon? What will be the weight of a person of 60 kg mass on the

moon? [Ans: 1.66 m/s2, 99.7N]

16. Study the table of specific heat capacities of the three different substances and answer the

following questions:

Substance Specific heat capacity

A 910 J/kg0C

B 380 J/kg0C

C 470 J/kg0C

i. What is meant by specific heat capacity of the substance A is 910 J/kg0C?

ii. Which one of the given substances will gain more temperature while heating equal

mass of all the three substances with equal amount of heat? Give reason.

iii. Which will go down more in depth while keeping equal mass at the three substances

heated for the same temperature of 1000C and kept on a wax slab, why?

17. In what way we use the neutralization reaction applied in our daily life? Write any three
examples.

18. Write any three application of ceramics.

19. How does artificial reproduction help in the excess production of fruits?

20. How would you conserve and manage the sources of water?

Group-D 4 × 4 = 16

21. Complete the ray diagram given alongside. Also, mention any

two nature of the image thus formed. If the power of hand lens

is +5D, what should be the distance between hand lens and

book to read it property?

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22. The given figure shows the laboratory preparation of ammonia gas. Answer the following
questions after observing the given figure.
i. Write the balanced chemical reaction of laboratory
preparation of ammonia gas by this method.
ii. Why is the mouth of hard glass test tube inclined
downward?
iii. Ammonia gas cannot be collected over water. Why?
iv. Which colour of litmus paper can help to confirm that the
gas jar is filled with ammonia gas?

23. Draw a chart to show both phenotype and genotype structure of the result obtained in
the first and second filial generation of offspring of mouse having black colour and white
colour according to Mendel’s experimental result. With the help of the same chart write
the ratio of phenotype and genotype of second generation.

24. Explain the evolution process occurred on the Mesozoic and Cenozoic era. Also, mention
their differences.



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