Astronomy_-_November_2020

Galileo as artist at the dawn of the telescope age p.24

NOVEMBER 2020

The world’s best-selling astronomy magazine

Galaxy
secrets
revealed

What the nearest galaxies
tell us about the universe p. 16

The strange history www.Astronomy.com Vol. 48 • Issue 11
of Jupiter’s moons p.46
BONUS
How the stars make gold p.40 ONLINE
CONTENT
Collect the cosmos in stamps p.50 CODE p. 4
Bob Berman on sketching at the eyepiece p.14



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Enter this code at: www.astronomy.com/code
VOL. 48, NO. 11
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ON THE COVER ON THE COVER: TARANTULA NEBULA: ESO/IDA/DANISH 1.5 M/R. GENDLER, C. C. THÖNE, C. FÉRON, AND J.-E. OVALDSEN. JUPITER: NASA, ESA, A. SIMON (GODDARD SPACE FLIGHT CENTER) AND M.H. WONG (UNIVERSITY OF CALIFORNIA, BERKELEY)

The Tarantula Nebula (NGC 2070)
is one of the largest star-forming
regions known, and lies within the
Large Magellanic Cloud.

CONTENTS 16 COLUMNS

FEATURES 32 46 Strange Universe 14

16 COVER STORY Sky This Month Observations of BOB BERMAN
Jupiter’s moons
A tale of two galaxies Planets shine morning Secret Sky 56
and night. MARTIN RATCLIFFE These remote satellites have
One large and one small, the revealed scant details to STEPHEN JAMES O’MEARA
Magellanic Clouds are familiar AND ALISTER LING earthbound observers for
sights in the southern sky — more than 400 years, and offer Observing Basics 58
and they can teach us a great 34 a great observing challenge.
deal about the Milky Way. GLENN CHAPLE
Star Dome and KLAUS BRASCH AND LEO AERTS
KNUT OLSEN Paths of the Planets Binocular Universe 60
50
24 RICHARD TALCOTT; PHIL HARRINGTON
ILLUSTRATIONS BY ROEN KELLY Collect the cosmos
How Galileo blended in stamps 7
science and art 40
While the universe is vast, this QUANTUM GRAVITY
Always drawing, sketching, or Gold from the stars selection of stamps can shrink
painting, Galileo Galilei saw it down to a manageable size. Everything you need to
the cosmos through an artist’s Humanity’s fascination with know about the universe
eye. DAN FALK this precious metal is increased KATRIN RAYNOR-EVANS this month: Perseverance
by knowing it comes from the begins its trip to Mars,
stars. RAYMOND SHUBINSKI 62 a hidden neutron star,
a new image of the Sun,
Ask Astro and more.

Spotting dark matter. IN EVERY ISSUE

ONLINE My Science Dave’s Picture of Sky This From the Editor 5
FAVORITES Shop Universe the Day Week Astro Letters 6
The inside Gorgeous Advertiser Index 61
Go to www.Astronomy.com Perfect gifts for scoop from photos from A daily digest Reader Gallery 64
your favorite the editor. our readers. of celestial Breakthrough 66
for info on the biggest news and science geeks. events.
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4 ASTRONOMY • NOVEMBER 2020

FROM THE EDITOR

Our little Editor David J. Eicher
neighbor galaxies Design Director LuAnn Williams Belter

The Large Magellanic Travelers to the Southern Hemisphere know that the sky EDITORIAL
Cloud is the most there is loaded with amazing sights, in some ways much Senior Editor Mark Zastrow
significant satellite richer than the sky we northerners are usually stuck with. Production Editor Elisa R. Neckar
galaxy of the Milky The jewel of the southern sky, the Large Magellanic Cloud (LMC) is Senior Associate Editor Alison Klesman
Way. It contains the a tiny barred spiral galaxy that orbits our Milky Way, lying at a dis- Associate Editor Jake Parks
Tarantula Nebula tance of 163,000 light-years. Found mostly in the constellation Associate Editor Caitlyn Buongiorno
(pink, upper right), Dorado, it shines at 1st magnitude and is so bright that it appears to Editorial Assistant Hailey McLaughlin
one of the largest naked-eye viewers as a detached portion of the Milky Way.
star-forming regions Lying relatively nearby in the sky is another little galaxy, the Small ART
known. ESO Magellanic Cloud (SMC), centered in the southern constellation Contributing Design Director Elizabeth M. Weber
Tucana. It is another barred spiral, some 200,000 light-years away, Illustrator Roen Kelly
that also appears as a detached portion of Milky Way nebulosity. Both Production Specialist Jodi Jeranek
these galaxies were “discovered” by sailors during Ferdinand
Magellan’s circumnavigation of the globe in 1519–1522, thus their CONTRIBUTING EDITORS
names. (But, of course, being naked-eye objects, they have been visible Michael E. Bakich, Bob Berman, Adam Block,
over the entirety of human history.) Glenn F. Chaple Jr., Martin George, Tony Hallas,
In his story, “A Tale of Two Galaxies” (page 16), Knut Olsen of the Phil Harrington, Korey Haynes, Jeff Hester, Alister Ling,
National Optical Astronomy Observatory describes his personal Stephen James O’Meara, Martin Ratcliffe, Raymond Shubinski,
encounters with the Magellanic Clouds. He has studied them using Richard Talcott
data from the Hubble Space Telescope, gazed at them during his observ-
ing time in Chile, and quite deeply pondered what they mean to us. SCIENCE GROUP
Olsen’s tale of discovery leads us to the significance of what the Executive Editor Becky Lang
Magellanic Clouds tell us. As satellites of the Milky Way, their com-
position and orbits hold secrets to both past and future. For example: EDITORIAL ADVISORY BOARD
In 1987, a telescope operator at Las Campanas Observatory in Chile Buzz Aldrin, Marcia Bartusiak, Jim Bell, Timothy Ferris,
spotted an unfamiliar star in the LMC. This turned out to be Alex Filippenko, Adam Frank, John S. Gallagher lll,
Supernova 1987A, the closest and brightest supernova observed on Daniel W. E. Green, William K. Hartmann, Paul Hodge,
Earth in nearly 400 years. Edward Kolb, Stephen P. Maran, Brian May, S. Alan Stern,
For years, astronomers have recognized that the LMC and SMC James Trefil
are an interacting pair of galaxies, and that a tidal stream of material
exists between them. They’ve found that the LMC has made off with Kalmbach Media
stars from its smaller neighbor, and that the future of the Clouds is
written in trouble. The two galaxies occasionally will slam into each Chief Executive Officer Dan Hickey
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sumed by the Milky Way, absorbed into our larger system of stars. Senior Vice President, Consumer Marketing Nicole McGuire
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WWW.ASTRONOMY.COM 5

ASTRO LETTERS

Perseverance blasted Getting ready for Mars Hats off to Kaler
off from Earth on
July 30, and is I just want to let you know The July special issue, “All About Stars,” was the best
planned to reach that I find Jake Parks’ issue of Astronomy ever! I always look forward to a
Mars in February articles in Astronomy to be learning experience when I read Astronomy, but this
2021. NASA/JPL-CALTECH some of the best written issue was a learning experience from cover to cover. I
— the piece on the NASA’s particularly enjoyed Jim Kaler’s comprehensive article
Perseverance probe is on the life of stars, but every single article was excellent.
absolutely fantastic! It’s Thanks for vastly increasing my understanding of the
clearly written, captures so stellar universe we live in. — Larry Crary, Stuart, FL
many interesting asides, is
beautifully illustrated, and At long last, a clear, concise, and complete description
was an absolute pleasure of how stars are born and die. The wonderful, fluid
to read. — Mike Schimpf, writing of Professor Emeritus Jim Kaler gives us a
picture rarely seen outside of textbooks and lengthy
Pacific Grove, CA treatises. While a lesser writer would be tempted to stop
and digress many times, Jim’s fluid writing caries us
Combining art through to completeness. I encourage all new students
and science of astronomy to clip this article and save it for future
reference. — Donald Craig Jr., Indianapolis, IN
As an artist, writer,
and science aficionado, I loved the way Bob Berman We welcome your comments at Astronomy Letters,
wound scientific notions with poetry in his article, “A P.O. Box 1612, Waukesha, WI 53187; or email to
Tribute to Carbon.” Not only was I introduced to new [email protected]. Please include your name, city,
information, it was done in such a beautiful, visual way. state, and country. Letters may be edited for space and clarity.
Good job! — Lynn Eckerle, Jackson, MI

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QG QUANTUM GRAVITYEVERYTHING YOU NEED TO KNOW ABOUT THE UNIVERSE THIS MONTH

SNAPSHOT

SOLAR ORBITER/EUI TEAM/ESA & NASA/CSL, IAS, MPS, PMOD/WRC, ROB, UCL/MSSL. BOTTOM FROM LEFT: NASA/BILL INGALLS; NAOJ; NASA/JPL-CALTECH/SWRI/ASI/INAF/JIRAM CAMPFIRES HOT DRAGON NOT SO VIEW FROM ABOVE
ON THE BYTES SPLASHDOWN SUPERMASSIVE NASA's Juno probe
SUN The SpaceX Crew The galaxy IC 750 has a made the first infrared
Dragon Endeavour lighter-than-expected map of the north pole
Solar Orbiter spacecraft safely supermassive black of Jupiter’s moon
captures the returned to Earth hole — less than Ganymede in 2019.
closest photos August 2 with 140,000 times the mass The ice there has no
of our star. NASA astronauts of the Sun, according to crystalline structure,
Bob Behnken and new data from the Very thanks to constant
On June 15, NASA and the Doug Hurley aboard. Long Baseline Array. plasma bombardment.
European Space Agency’s
Solar Orbiter made its first close
pass of the Sun, coming within
48 million miles (77 million
kilometers) of our star. During
the pass, the spacecraft’s suite
of 10 instruments went to work,
snapping the closest images of
the Sun ever taken. The shots
were meant simply to confirm
the instruments are working
properly. But they also revealed
a new discovery: an army of
small bright spots, each about
one-millionth to one-billionth
the size of a regular solar flare,
all over the Sun. Scientists are
now calling them campfires.

It’s possible campfires are
miniature versions of the flares
we spot from Earth. But they also
may be related to nanoflares —
small, brief, ubiquitous bursts of
energy across the Sun thought to
heat the corona (the Sun’s outer
atmosphere). The Solar Orbiter
team now plans to measure the
campfires’ temperatures, which
should reveal whether they’re just
mini solar flares or an important
heating mechanism for the
corona. —ALISON KLESMAN

WWW.ASTRONOMY.COM 7

QUANTUM GRAVITY

PERSEVERANCE BEGINS JOURNEY
TO THE RED PLANET

The rover will search for signs of ancient martian life, pluck oxygen
from Mars’ thin air, and gather samples for a future return mission.

After years of anticipation, in the past, looking for signs of ancient BLAST OFF. Perseverance lifts off aboard
NASA’s latest robotic explorer, the microbes within rocks and collecting
Perseverance rover, blasted off for Mars promising samples for a future return a United Launch Alliance Atlas V rocket the
July 30 at 7:50 A.M. EDT. Departing mission. But it also was designed with morning of July 30, officially kicking off the
atop an Atlas V-541 rocket from the the intention of paving the way for Mars 2020 mission. The rover will arrive at
historic Space Launch Complex 41 at human exploration. Mars on February 18, 2021. UNITED LAUNCH ALLIANCE
Cape Canaveral Air Force Station in
Florida, the ambitious rover is the latest "With the launch of Perseverance, PERSEVERANCE’S TOOLKIT
in the space agency’s long lineage of we begin another historic mission of
Red Planet explorers. Perseverance is exploration," NASA Administrator The new rover carries a sophisticated
expected to land in Mars’ Jezero Crater Jim Bridenstine said in a statement. suite of instruments capable of
on February 18, 2021. "This amazing explorer’s journey has collecting and preparing samples
The $2.7-billion mission will seek already required the very best from all that will one day be returned to
out sites that were potentially habitable of us to get it to launch through these Earth. Perseverance will drill into
challenging times.” intriguing rocks, seal samples in
titanium tubes, and deposit them on
the martian surface for a future (and
so far, unplanned) mission to pick
up and deliver back to Earth. Once
here, researchers will scrutinize them
in laboratories with more powerful
equipment than can be sent to Mars.

8 ASTRONOMY • NOVEMBER 2020

LAUNCHING A MISSION TO MARS QUICK
TAKES
PROPER LAUNCH WINDOW Spacecraft
is pulled into JAMES WEBB DELAYED
Earth Mars Mars’ orbit.
Sun Spacecraft and Spacecraft Due to technical challenges and the
Mars arrive at the is pulled ongoing COVID-19 pandemic, the
same place. back toward
Earth’s orbit. target launch date for NASA’s James
LAUNCHED TOO LATE OR TOO EARLY Webb Space Telescope has been
pushed back from March 2021
Earth Mars to October 31, 2021.

Sun Size and distance ASTRONOMY: ROEN KELLY SENDING MARS HOPE
Spacecraft misses not to scale.
Mars and cannot In July, the United Arab Emirates
be captured. became the first Arab nation to
launch an interplanetary probe. The
THE RIGHT TIMING. When sending a spacecraft to the Red FAST FACT spacecraft, named al-Amal (Hope),
will arrive at Mars in February 2021 for
Planet, efficiency is key. Since space travel isn’t cheap, any In 2003, Mars a two-year mission to study the Red
craft leaving Earth needs the perfect window of opportunity. came within Planet’s dynamic atmosphere.
The course between two circular orbits that uses the least 35 million
FILLING THE VOID
energy is known as the Hohmann transfer orbit. In the case of miles
New data from the Sloan Digital Sky
travel between Earth and Mars, a rocket flings the object away (56 million Survey has allowed astronomers to
create the largest-yet 3D map of the
from Earth and into an elliptical orbit around the Sun. The kilometers) universe, filling in gaps about how it
expanded over the past 11 billion years.
craft coasts around to meet Mars on the other side, arriving of Earth,
within seven to nine months. Mars and Earth don’t have marking the ULTIMATE TELESCOPE
perfectly circular orbits, so launch windows are also timed for
when the planets are closest to each other. But this window planets’ A 100-meter-wide telescope on the
only opens every 26 months, meaning delays can force closest Moon would be powerful enough to
missions to wait until the planets align again. — CAITLYN BUONGIORNO approach in detect the cosmos’ first generation of
60,000 years. stars, says a team at the University of
Texas. They’ve dubbed the fanciful
Perseverance is also ferrying a small the atmosphere. Also a proof-of-concept facility the Ultimately Large Telescope.
helicopter drone named Ingenuity, just experiment, the technology could one
under 2 feet (0.6 meter) tall and weigh- day support astronauts or even produce WHAT A VIEW
ing less than 4 pounds (1.8 kilograms). locally sourced rocket fuel.
Intended as a technology demonstra- The spot on Earth with the steadiest
tion, Ingenuity can take off, hover a few If astronauts eventually gain access skies for astronomy is atop Dome A, an
dozen feet above the surface, and land to water on Mars — a reliable source Antarctic ice dome, according to a new
on flat ground. of hydrogen — scientists can tweak study. The previous record-holder for
MOXIE’s basic technology to make
Another mission objective is to pave more complicated products, Michael the site with the least atmospheric
the way for humans to explore Mars. Hecht, MOXIE’s principal investigator, turbulence (which distorts images)
The rover is carrying the Mars Oxygen tells Astronomy. “Once you have water
In-Situ Resource Utilization Experiment and you have electrochemistry,” Hecht was Dome C, also in Antarctica.
(MOXIE), which will use electricity to says, “you can start making anything
extract oxygen from carbon dioxide in from paraffin to beer.” — JAKE PARKS VENUSIAN VOLCANISM

Scientists have discovered 37
volcanoes on Venus that are still
active. The new work, which suggests
the interior of the planet is still
churning, may help researchers
choose geologically active locations

for future missions to target.

DANCING PLANETS

For the first time, researchers have
used a ground-based telescope to
detect two exoplanets orbiting in
a resonance that allows them to
gravitationally interact, tugging on
each other and disrupting the timing
of their passes. — MARK ZASTROW, C.B., J.P.

QUANTUM GRAVITY JAMES JOSEPHIDES (SWINBURNE ASTRONOMY PRODUCTIONS) AND THE S5 COLLABORATION

A neutron star lurking
in Supernova 1987A

On February 24, 1987, an unex- THE BLOB. ALMA RISING
pected cosmic explosion rocked FROM THE
the astronomical community. Dubbed captured high-resolution ASHES
Supernova 1987A (SN 1987A), the fiery images that revealed a hot,
event — triggered by the implosion of a slightly off-center “blob” The Milky Way is home
massive star — was the closest observed (inset) within the core of to around 150 globular
supernova since the invention of the tele- Supernova 1987A. The clusters — compact col-
scope. It occurred just 170,000 light-years material seen by ALMA in lections of stars orbiting
away in the Large Magellanic Cloud, a radio wavelengths is largely in the far reaches
satellite galaxy of the Milky Way. SN 1987A colored red and yellow. of the galactic halo. Stars
was so bright that naked-eye observers Hubble’s visible view is in these ancient clusters
could spot it for several weeks. displayed in green and are old enough to have
The event wasn’t just a visual feast. It Chandra’s X-ray view is watched the Milky Way
also gave astronomers an unprecedented shown in blue. grow up over billions of
opportunity to investigate the processes years. But sometimes,
that trigger supernovae, as well as how these ALMA (ESO/NAOJ/NRAO), P. CIGAN AND gravitational forces
powerful blasts ripple through their sur- R. INDEBETOUW; NRAO/AUI/NSF, B. SAXTON; wrench star clusters
roundings. Despite their destructive power, NASA/ESA apart. Recently, scientists
supernovae leave remnants, typically in the discovered one such
form of a black hole or neutron star, depend- ALMA’s high-resolution images revealed unlucky cluster: The
ing on the mass of the exploding star. In the a hot “blob” lurking in the core of SN Phoenix Stream was
case of SN 1987A, one mystery has endured: 1987A, located right where astronomers torn apart by our galaxy
What did the blast leave behind? think its suspected neutron star should be. more than 2 billion years
In a new paper published July 30 in The blob itself is not the neutron star — ago. It is likely that the
The Astrophysical Journal, astronomers because neutron stars compress about 1.4 Phoenix Stream will one
report they’ve found compelling evidence times the mass of the Sun into a sphere just day be absorbed into the
that SN 1987A is still harboring a neutron 15 miles (25 kilometers) across, they are Milky Way, ultimately
star, which, at just 33 years old, would impossible to see directly. following a path similar
make it the youngest such stellar corpse to other ancient clusters
yet found. Using the Atacama Large Instead, the blob is a giant gas cloud that have long since
Millimeter/submillimeter Array (ALMA) dramatically outshining its surroundings. disappeared. — C.B.
radio telescope in Chile, they were able to It spans about 4,000 astronomical units —
pierce through the dust and gas left behind 1 astronomical unit, or AU, is the average
by the supernova to see what lies within. Earth-Sun distance — and it’s estimated to
have a temperature of some 9 million degrees
Fahrenheit (5 million degrees Celsius).

“There has to be something in the
cloud that has heated up the dust and
which makes it shine,” co-author Mikako
Matsuura of Cardiff University said in a
press release. She argues the most likely
culprit is a neutron star, dubbed NS 1987A.

Now that astronomers have found the
likely location of the neutron star, the
real quest for understanding can begin.
One question is whether NS 1987A is a
run-of-the-mill neutron star or a pulsar
— a more exotic type of neutron star that
emits powerful beams of radiation as
it spins. To find out, astronomers must
continue to monitor the blob for periodic
variations in its brightness that might give
away the consistent rhythm of a pulsar
within. — YVETTE CENDES

10 ASTRONOMY • NOVEMBER 2020

You’re contemplating a photograph of 550 million pixels..
But you can only see a small part of it.

Immersive and interactive
online exploration

vaonis.com/mosaic

Stellina,
the observation station that
simplifies astronomy reveals
one of the Universe’s most
magnificent images.

QUANTUM GRAVITY

Black hole loses its crown DECROWNED. The left panel of this artist’s
— then gets it back
rendering shows a black hole consuming a star
Ravenous supermassive black optical and ultraviolet light. But then, (the red trail). This process disrupts gas within
holes at the centers of galaxies are X-ray telescopes including NASA’s the accretion disk surrounding the black hole
often accompanied by a glowing corona Neutron star Interior Composition (yellow-orange), potentially cutting off the black
of superhot gas, which hovers around the Explorer mounted to the International hole’s corona — a cloud of ultra-hot electrons
black hole and emits powerful X-rays. Space Station, plus three other NASA that shines brightly in X-rays (white) — from
These X-rays can vary significantly in and European Space Agency space its source of power. NASA/JPL-CALTECH
brightness over time, flickering under the telescopes, watched the black hole’s
influence of the processes that power them. X-ray corona abruptly disappear. The of MIT in a press release. Even more
In March 2018, astronomers around observations were published in The curious: Over the next 100 days, the
the world aimed their telescopes at a Astrophysical Journal Letters July 15. corona reappeared, gathering strength
galaxy roughly 270 million light-years until it was ultimately 20 times brighter
away named 1ES 1927+654, whose central Over the course of 40 days, the than it originally had been.
black hole was spotted undergoing a par- corona faded to a mere 1/10,000
ticularly dramatic transformation, flaring its original brightness. “It became The team speculate that the dramatic
up to 40 times its original brightness in undetectable, which we have never seen death and rebirth of the X-ray corona
before,” said study co-author Erin Kara may have occurred as the supermassive
black hole gobbled up a star, ripping it
apart in the process. Simulations pub-
lished last year show that during such an
event, called a tidal disruption, the stream
of debris would collide with the accretion
disk of gas that circles a black hole’s event
horizon. This would cause the inner disk
to quickly fall in and disappear. Without
the disk’s magnetic field to feed on, the
corona would be cut off from its energy
source and vanish — only to gradually
rebuild itself as material originally
farther out in the accretion disk flowed
inward to replenish the inner disk.

But how exactly a black hole’s
corona is powered remains unclear.
Astronomers hope more observations of
events like this one can help them better
pin down the source of the corona’s
energy. — M.Z.

19 Two exoplanets seen circling a Sun-like star ESO/BOHN ET AL.

The number Astronomers using the European Southern Observatory’s
of asteroids in Very Large Telescope (VLT) have captured the first-ever image
our outer solar of multiple worlds circling a star that resembles a younger
system recently version of our Sun. The system, called TYC 8998-760-1, is roughly
determined by 300 light-years away in the southern constellation Musca.
researchers at
São Paulo State The inner planet lies about 160 astronomical units from its
University to have host star (1 astronomical unit, or AU, is the average Earth–Sun
origins in other distance) and is roughly 14 times the mass of Jupiter. The more
star systems. distant planet is located about 320 AU from its star and weighs
about 6 Jupiter masses. To make such a challenging detection,
the VLT used its state-of-the-art adaptive optics to correct for
image distortion caused by Earth’s turbulent atmosphere, and a
coronagraph to help block excess light from the target star. —M.Z.

12 ASTRONOMY • NOVEMBER 2020

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STRANGE UNIVERSE — and most of us do, at least some of the time — your
sky session brims with distractive choices. Should I

change to a binoviewer? Phone a friend to join me? Insert

a filter? Take some pictures? Boost the magnification?

Anatomy of the View something else?
In some states, teachers now give instruction in

mindfulness. Children take to it readily and it converts

observer restless, knee-shaking energy into a quiet, enjoyable
focus on whatever is in front of them. For adults, medita-
tion does the same thing. Calmly placing full attention

Amateur astronomers are, by nature, mindful watchers. on a single object, whether one’s breath or a candle’s
flame, helps the mind perceive whatever’s happening

with a pleasurable clarity that’s absent when attention

darts between myriad things or mental chatter.

Observing — extensively watching an object — is a

quiet activity with focused attention, a form of medita-

tion. It is like nothing else. We observers are mindful

without trying. By losing ourselves in the countless

details of whatever’s in the eyepiece, we “grok” the celes-

tial object with a satisfying completeness.

It’s said that backyard astronomers perform useful

science and, while that’s sometimes true, it’s more often

the case that the activity is as wonderfully purposeless

as playing jazz. Or, if one must cite a goal, it’s simply to

be amazed, or to have revelations.

For example, there’s a break in the lunar Apennine

mountain chain, a gap equaling the distance between

Washington, D.C., and Baltimore. It looks like a place

where lava flowed. But which way? A careful look-see

reveals wrinkle patterns that make it clear the magma

went from Mare Serenitatis into Mare Imbrium, not the

other way around. Good luck getting anyone else excited

about this — but, for observers, seeing exactly what hap-

pened 3.8 billion years ago confers an oddly profound

Astronomy Editor Astronomy Editor David J. Eicher recently satisfaction.
Dave Eicher made shared a drawing he’d made long ago at the Sometimes it’s not details that hold our focus.
this sketch of M13 in eyepiece of his 17.5-inch reflector. Myriad dots
Hercules years ago, depict a globular cluster, M13. But what the sketch really Sometimes the pleasure comes from observing some-
using a 17.5-inch f/4.5 reveals is patience — and that introduces thing intensely alien. Who among us hasn’t deliberately
reflector at 50x. looked at the 8th-magnitude star HDE 226868 in

DAVID J. EICHER Cygnus solely because, once a week, this

today’s topic: the makeup of an observer. Observing — massive star is hurled around like a wrestler
Being an observer is a quality you and I extensively flung disrespectfully by its companion X-1,
the sky’s surest black hole? There’s nothing
have in common. In the 21st century, it’s an

attribute unusual enough to merit examina- watching an visually special here. And yet we cannot
tion. That’s because modern humans tend object — is a resist.
to be busy and non-observational. This quiet activity
busyness means we are often scattered and with focused And who hasn’t taken the trouble to
unfocused. attention, a observe the violent version of West Side
Story unfolding in Virgo? This is the strange,
In seeking examples of common activities blue, near-lightspeed jet being hurled off the

in which one might naturally be an observer, form of west side of the monster galaxy M87. Its
motorcycling comes to mind. On my big old meditation. color largely comes from Cherenkov radia-
800-pound (363 kilograms) touring bike, tion, emitted when electrons break the light-

the word touring suggests I get to watch the speed barrier. How can we not stare?

BY BOB BERMAN changing scenery in a relaxed manner. But no such luck. And how can I not feel a kinship with you, my fellow

Bob’s newest book, A biker’s attention is typically split in multiple direc- observers, at star parties and meets? Our bodies may be
Earth-Shattering tions. You’re obsessively watching the road for ruts and just as carbon-based as the other 8 billion members of
(Little, Brown and gravel, while also focusing on the edge of the woods to Homo bewilderus. But we are not like them.
Company, 2019), spot any deer ready to spring out.
explores the greatest BROWSE THE “STRANGE UNIVERSE” ARCHIVE
cataclysms that have It’s not usually very relaxing. And neither is using a AT www.Astronomy.com/Berman
shaken the universe. telescope, if we’re honest. If you have a restless mind

14 ASTRONOMY • NOVEMBER 2020

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A tale of TWO
One large and one
small, the Magellanic I FIRST SAW THE MAGELLANIC
Clouds are familiar
sights in the southern Clouds with my own eyes when I arrived
sky — and they can at the Cerro Tololo Inter-American
teach us a great deal Observatory (CTIO) as a postdoctoral
about the Milky Way. researcher in 1998. The Large and Small
Magellanic Clouds (LMC and SMC) —
BY KNUT OLSEN a pair of dwarf galaxy companions to
the Milky Way — had, of course, been
observed by countless people before. But
it still felt surreal to marvel at them while
standing in a dark Chilean desert.

The clouds are part of the culture and
lore of many groups of Indigenous peoples
in South America, Australia, and southern
Africa, where they were named to represent
things like the feathers of rheas, a South
American relative of the ostrich; the tracks
of celestial animals (Setlhako); a pair of
cranes (Prolggi); and an old couple sitting
by a campfire (Jukara). Polynesian and
European sailors also used the Magellanic
Clouds as celestial guides, and Europeans
later named them to recognize Ferdinand
Magellan’s 16th-century circumnavigation
of the globe.

16 ASTRONOMY • NOVEMBER 2020

The Milky Way stretches above
Cerro Tololo Inter-American
Observatory, where the author
worked for eight years studying the
Large Magellanic Cloud (lower left)
and the Small Magellanic Cloud
(upper left). ANJA VON DER LINDEN

GALAXIES

This stunning ground-based The SMC is chock-full of obscuring
image of the LMC reveals the clouds of interstellar dust that block
largest star-forming region in visible light. But the European Southern
our Local Group of galaxies: Observatory’s Visible and Infrared
the Tarantula Nebula, also Survey Telescope for Astronomy,
known as 30 Doradus (the equipped with infrared capabilities,
bright red patch slightly left allows astronomers to peer through the
of center). ECKHARD SLAWIK dust, revealing myriad stars. ESO/VISTA VMC

WWW.ASTRONOMY.COM 17

The Milky Way’s Orion Nebula, seen in this
composite image captured by the Hubble
Space Telescope, is the closest massive
star-forming region to Earth.

The Tarantula Nebula (30 Doradus), located in In fact, they’ve been featured in more at night! At the center of 30 Doradus is ORION NEBULA: NASA, ESA, M. ROBBERTO (SPACE TELESCOPE SCIENCE INSTITUTE/ESA) AND THE HUBBLE SPACE TELESCOPE ORION TREASURY PROJECT TEAM
the LMC, is the most luminous known starburst than 15,000 research papers, a total a dense, massive cluster of stars called
region in the Local Group of galaxies. DAMIAN PEACH to which my thesis added two. There R136, which, with an age less than about
are many reasons for their popular- 2 million years, houses stars so young
But what made seeing the LMC and ity, including their proximity. They that even the most massive members
SMC special to me was that I had spent are as nearby as galaxies get, roughly have yet to finish their short lives.
the previous three years working with 160,000 light-years for the LMC and
data on the clouds, collected by the some 200,000 light-years for the SMC. The stars just outside R136 but still
Hubble Space Telescope. This served as This means they are close enough to be within 30 Doradus formed a few million
the basis of my Ph.D. thesis, which studied in detail, yet far enough away years earlier, giving them more time to
focused on the star formation history and that their stars can be approximated as evolve. The light from one of these stars,
the oldest star clusters in the LMC. Yet I being at uniform distances — unlike caught in the act of ending its brief
had never seen the clouds in person. those of the Milky Way, where it can be career by exploding as a supernova,
difficult to see the forest for the trees. famously first reached Earth in 1987.
My Ph.D. adviser at the University of (At that point, I was in high school and
Washington, astronomer Paul Hodge, The clouds also have a number of more interested in electric guitars than
who sadly passed away late last year, had notable features, such as the LMC’s astronomy.) Oscar Duhalde, a telescope
taken a boat to South Africa and spent Tarantula Nebula, usually referred to operator at Las Campanas Observatory,
weeks at Boyden Observatory to collect as 30 Doradus, which is the largest discovered the unfamiliar “new” LMC
his own thesis data on the clouds. But my star-forming region in our Local Group star when he stepped outside to gaze at
data had arrived on digital tapes in the of galaxies. Northern Hemisphere astron- the skies. The event, named SN 1987A,
mail. Moving to Chile was going to be omers are generally more familiar with kicked off a frenzy of observations and
the start of my own scientific adventure. the Orion Nebula (M42), a nursery for renewed focus on the study of supernova
And my personal encounter with the massive stars in our own galaxy. But, explosions, particularly how they can be
Magellanic Clouds surely was an if placed at the distance of the Orion used to measure distances. This culmi-
unforgettable experience. Nebula, 30 Doradus would span across nated in the 1998 discovery of dark
one-fifth the sky, even casting shadows energy by two supernova survey teams.
The Magellanic Clouds
My journey to the clouds
Besides being spectacular nighttime
objects, the Magellanic Clouds are popu- Because massive stars evolve quickly and
lar targets for professional astronomers. with high complexity, they challenge
our ability to model and understand the
physical processes that occur within
them. Phil Massey is one of the promi-
nent astronomers who have spent their
careers studying them. In 2001, he was

18 ASTRONOMY • NOVEMBER 2020

scheduled to observe the LMC’s red ODDLY ORBITING STARS
supergiants, which evolved from stars
with masses between about 10 and 25 –69 km/s 66 km/s
times the mass of the Sun, but his travel
plans were interrupted by the tragedy of The LMC is tilted with respect to our line of sight. As its disk spins clockwise, the stars at the
September 11. top right appear to recede, stretching (or redshifting) their light to redder wavelengths. In the
same way, the stars at the bottom left appear to approach us, blueshifting their light to shorter
I was both the local instrument scien- wavelengths. About 95 percent of the LMC’s stars follow this pattern, but the other 5 percent
tist for the spectrograph Massey was — shown here as red and blue circles, indicating whether their light is redshifted or blueshifted,
scheduled to use and had overlapping respectively — have the opposite pattern. The deviation suggests these stars did not originate
scientific interests, so he invited me to in the LMC, but instead have been captured by the LMC from the SMC. SPITZER IMAGE: MARGARET MEIXNER
join the project if I would collect the
data. The Blanco 4-meter telescope’s AND KARL GORDON (SPACE TELESCOPE SCIENCE INSTITUTE/AURA/NASA); COMPILATION BY K. OLSEN (NOIRLAB/AURA/NSF)
Hydra-CTIO spectrograph was a finicky
instrument, but it had great capabilities. faster the supergiants were moving, the has since stood the test of time; it is now
It could collect light from more than 100 more Doppler shifted their spectra would central to our consensus understanding
objects at a time using optical fibers be. To determine their speeds, I would that galaxies formed through the settling
mounted to small magnetic buttons that digitally slide each star’s spectrum over a of ordinary matter onto concentrated
were precisely placed on a metal plate by reference spectrum for which I knew the dark matter halos.
a high-speed robotic arm. corresponding velocity. I’d then simply
measure the shift between the lines. The presence of dark matter means
When it worked smoothly, watching it that the stars located in the outskirts of
go was pure joy. The spectra, which chart In the 1970s, Vera Rubin and other disk-shaped galaxies typically maintain
an object’s light across a range of ener- astronomers used similar techniques to constant high orbital speeds, despite the
gies, rolled in by the dozens. But when it measure the velocities of the stars orbit- fact they are far from their galactic cores.
misbehaved, it was misery, forcing trips ing in galaxies such as Andromeda and In other words, the galaxies’ rotation
to the Cassegrain cage where it was M33. They found that as they looked curves are “flat.” And because the red
mounted to the telescope to disentangle farther from the galactic centers, the supergiants located in the outskirts of
a rat’s nest of crossed fibers, leading to orbital velocities were too high to be the LMC fall on a flat rotation curve,
hours of lost time. Luckily, Massey’s run explained by just the gravitational pull they indicate the Milky Way’s largest
was scheduled right after two nights of from the luminous matter within the satellite galaxy also has a significant
work aimed at fixing Hydra’s technical galaxies. This discovery of dark matter amount of dark matter.
problems. The observing run was nearly
flawless, yielding hundreds of spectra of
LMC red supergiants.

From those and other spectra, Massey,
along with astronomer Emily Levesque of
the University of Washington, developed
techniques to measure the temperatures
of red supergiants, resulting in a revised
temperature scale that resolved a previ-
ous disagreement with theoretical stellar
models. They also identified several stars
with radii of about 1,500 times that of the
Sun, making them some of the largest
stars known.

The pair also recently applied these
techniques to observations of the red
supergiant Betelgeuse, demonstrating
that the star’s temperature had changed
little even while it famously dimmed by
more than a magnitude. They concluded
that the dimming was caused by an epi-
sodic release of dust grains from the
star’s atmosphere.

My own interest in red supergiants
lay in using them as probes of the LMC’s
gravitational structure. The spectra of
the stars allowed us to measure their
velocities along the line of sight. The

WWW.ASTRONOMY.COM 19

ECHOES OF SUPERNOVA 1987A have to be moving at the speed of light.
He soon looked at the full-size difference
TOP LEFT: The LMC’s ethereal nebulosity and rich star field are apparent in this October 2001 image. images, rather than the postage stamp
TOP RIGHT: Subtracting the first shot from a second image taken in December 2001 highlights changes versions, and noticed that the ghosts
in brightness, revealing a nested set of circles. White pixels were brighter in the December image, formed concentric circles on the sky. At
black pixels were fainter, and gray pixels did not change. BOTTOM ROW: Subtracting the original shot the center of those circles was SN 1987A.
from others taken in 2002 (left) and 2004 (right) shows that the circles are rippling outward from the
center — the site of SN 1987A — at the speed of light. These echoes are reflected light from the original We were seeing light echoes — the
supernova, observed almost 20 years after the initial blast. ARMIN REST (HARVARD)/SUPERMACHO/EHS COLLABORATION original light from the supernova
reflected off surrounding dust clouds in
Dark matter leads dark matter, but more events are needed the LMC, like sound waves bouncing
to light echoes before definitive conclusions can be made. through the Alps. The echoed light’s
pinball path meant it took extra time to
Fifty years after its discovery, we still Around 2005, I participated in a make it to Earth, arriving about 15 years
don’t know what dark matter is made of project led by physicist Christopher after the light that came straight from
— but not for lack of trying. In the 1990s, Stubbs of Harvard University and astron- the supernova. These light echoes form
a leading candidate for the composition omer Armin Rest of the Space Telescope rings tracing the surfaces of surrounding
of dark matter was massive compact halo Science Institute, in which we observed dust clouds that are located the same dis-
objects (MACHOs): unseen black holes, fields in the LMC every other night. The tances from the supernova. Individual
neutron stars, or dim brown dwarfs. goal was to detect brightness changes rings with different radii represent
in stars that would be indicative of reflections from sheets of dust at differ-
Several groups looked for signs of such microlensing events. Rest developed soft- ent distances from the explosion. It
objects by observing stars in the LMC ware that subtracted every microlensed turned out that these light echoes had
and hoping to catch the sudden brighten- image from a previous template image, been discovered before by another proj-
ing that would occur if a MACHO passed carefully tracking the offsets, distortions, ect, so we had simply rediscovered them.
directly in front of it. The foreground and resolution of the pair. He would then
MACHO would act as a gravitational identify objects that varied between the But as Rest continued to scrutinize
lens, with its invisible mass bending the two images and trace how their bright- the observations, he started finding
light rays from the background star and nesses evolved over time. The team additional light echoes with arcs that
amplifying the light we see. (This is would visually scour these light curves, corresponded to locations other than
technically an example of a microlens, as well as postage stamp-sized versions that of SN 1987A. These new echoes
because the distorted shape of the of the difference images, separating true were from supernovae that had exploded
background star would be measured in astronomical objects from image artifacts in the LMC centuries ago, yet we were
micro-arcseconds.) The result would be and other junk. still seeing the original explosions
a predictable increase in brightness of in delayed form. These light echoes
the background star as the MACHO In late 2003, Gajus Miknaitis, then revealed a unique way to study superno-
approached, followed by a dimming as it a graduate student at the University of vae long after their initial blasts. And
moved away; the whole event might last Washington working on the project, while our project ultimately did not find
for hours, days, or weeks. Astronomers found strange objects that he called compelling evidence for MACHOs as an
have found a few microlensing events in “moving nebular ghosts.” I calculated important source of dark matter, we still
the LMC, and thus a potential source of that if these were in the LMC, they would found something totally unexpected —
and potentially quite powerful.

Following my work analyzing red
supergiants in the LMC, my colleagues
and I used the Hydra-CTIO spectro-
graph to measure velocities of other stars
in the LMC. We concentrated on stars
much older than the young red supergi-
ants to see how the passage of billions of
years would affect their dynamics, and
eventually gathered thousands of spectra.

After dissecting the data, we found
that most of these older stars had veloci-
ties that traced the same flat rotation
curve as the red supergiants; however,
they also exhibited a bit more random
noise, which is expected given they’ve
experienced billions of years of orbital
evolution. But roughly 5 to 10 percent of
the total had velocities that suggest they

20 ASTRONOMY • NOVEMBER 2020

are orbiting in the opposite direction as A COSMIC CONNECTION
the rest — very strange! It would be just
as weird if one of the planets in our own Leading
solar system orbited the Sun in the arm
wrong direction.
SMC LMC
Because we could only measure the Magellanic Stream
velocity of the stars along the line of sight Magellanic
(motion toward or away from us), Bridge
another possibility was that the stars are
orbiting in the same direction as the rest The Magellanic Stream stretches almost halfway around the Milky Way, as revealed by 21-centimeter
but are highly inclined, traveling well (radio) emissions from neutral hydrogen atoms (pink). This long stream of gas leads and trails behind
above and below the disk of the LMC. the LMC and SMC, as well as connects the two clouds via a bridge of neutral hydrogen.
We concluded this was a more likely
situation, and recently confirmed it by
obtaining full 3D velocities of the stars
using data from the Gaia satellite. But
that still didn’t explain how this small
subset of oddly orbiting stars got on
their current track.

MAGELLANIC STREAM MAP: L. NIDEVER, ET AL., NRAO/AUI/NSF AND MELLINGER, LEIDEN/ARGENTINE/BONN SURVEY, PARKES OBSERVATORY, WESTERBORK OBSERVATORY, AND ARECIBO OBSERVATORY Tracing stars back of neutral hydrogen gas that astrono- 30 Doradus. Viewed from the LMC, the
through time mer David Nidever of Montana State streamers have the same velocities as
University found extends over more those of the strangely moving stars we
We have known for a long time that than half the sky. had previously found. Moreover, we
the LMC and SMC are a pair of gravi- measured the abundance of iron in some
tationally interacting galaxies. The This ribbon includes streamers that of our weird stars, finding they had
most obvious result of this interaction connect to both the LMC and SMC, with surprisingly little iron compared to other
is the Magellanic Stream and its lead- two of these filaments converging on stars in the LMC. However, they were
ing arm, which form of a twisted ribbon a good match for SMC stars.

MIXING THE MAGELLANIC CLOUDS Based on the streamers and seemingly
migrant stars, we concluded that the
Magellanic latitude 20 LMC had stolen stars from its smaller
0 Magellanic Stream sibling, the SMC. These displaced stars
are now orbiting in front of and behind
–20 LMC disc the LMC’s disk. Plus, the arms connect-
ing the LMC and SMC were apparently
–40 Combined stars of The orbital trajectory ripped out along with these stars and are
the LMC and SMC of the LMC and SMC now falling onto the LMC’s disk, right at
the location of 30 Doradus. This scenario
Magellanic latitude 20 would explain why 30 Doradus is form-
0 Magellanic Stream ing stars so aggressively. The infalling
material provides external pressure on
–20 LMC disc The orbital trajectory 30 Doradus and keeps the stellar winds
of the LMC and SMC and supernovae within from completely
–40 Stars of SMC blowing away the nearby gas, which
would halt further star formation. These
50 0 –50 –100 –150 ripped-out, massive stars might also be
Magellanic longitude the source of the microlensing events
that were seen in the 1990s, which would
A simulated collision of the LMC and SMC reproduces many of the observed features of the Magellanic further rule out MACHOs as a signifi-
system, including the leading arm and trailing stream of material, as well as the presence of SMC stars cant source of dark matter scattered
in the LMC’s disk. The top panel shows the combined stars of the LMC and SMC in the simulation, throughout the Milky Way.
while the bottom panel shows only the SMC stars, demonstrating that most of the stellar debris
polluting the system likely originates from the SMC. GURTINA BESLA; REPRODUCED FROM BESLA ET AL.2013, MONTHLY NOTICES With better data and more sophisti-
cated theoretical models, exactly how the
OF THE ROYAL ASTRONOMICAL SOCIETY, 428, 2342 Magellanic Clouds have been interacting
with each other over the eons is becom-
ing clearer by the year. Astronomer Nitya

WWW.ASTRONOMY.COM 21

LEFT: The powerful
Dark Energy Camera,
with its 2.2° field of
view, features 62
charged-coupled
devices (seen in blue),
allowing it to capture
570-megapixel images.

U.S. DEPARTMENT OF ENERGY

RIGHT: The 4-meter
Blanco Telescope
(center) and its Dark
Energy Camera are
an ideal pair for
investigating the LMC
and SMC. FERMILAB VISUAL

MEDIA SERVICES

Kallivayalil of the University of Virginia University of Wisconsin-Madison and The Victor M. Blanco Telescope in
and others have been hard at work mea- the other by Sergey Koposov of Carnegie Chile collects observations for the Dark
suring the 3D motions of nearby galaxies, Mellon University — used the DES data Energy Survey, as a nearby astronomer
including the Magellanic Clouds. They to discover eight new extremely faint, takes in the spectacular night sky and
have determined that the clouds are only low-mass dwarf galaxies. Some of these the goliath scope. ESO/A. TUDORICĂ
loosely bound, if at all, to the Milky Way. galactic specters have locations, dis-
Astronomer Gurtina Besla of Steward tances, and velocities that make them while simultaneously accelerating toward
Observatory has led work to model the likely satellites of the Magellanic Clouds the Milky Way. As they race to meet our
motions of the clouds, finding that the — in other words, satellites of satellites. galaxy, they occasionally slam into each
LMC and SMC have made several close other, tossing out great plumes of stars
passes over the past few billion years — The Survey of the MAgellanic Stellar and gas both ahead of and behind them.
and that they likely collided with each History, or SMASH, collaboration, led by During their tango, the pair occasionally
other about 300 million years ago. Nidever, and the DES Collaboration have flares up as colliding gas kicks off bursts
also found stars from the Magellanic of intense star formation. And all the
Such a collision would naturally Clouds as far as 20° from the LMC and while, a small audience of faint dwarf
explain how the LMC stripped stars and SMC, showing that they extend much satellites sits on the periphery.
gas from the SMC, as well as how the farther than previously thought. Finally,
Magellanic Stream formed. Furthermore, astronomers Vasily Belokurov of the Some of this picture might be exag-
it predicts that stars from the clouds University of Cambridge and Denis Erkal gerated by my imagination, but it is also
should have been flung far from their of the University of Surrey have used data almost certainly missing some fascinat-
parent galaxies, meaning they’d now from the Gaia satellite to map the clouds’ ing details that I couldn’t yet dream of.
be spread out over large areas of the stars with stunning detail. Their 2018 I’ve learned that scientific research is like
Southern Hemisphere’s night sky. This paper, “Clouds in arms,” shows that the jumping into a canoe on an uncharted
is why my current interest, and that of SMC and LMC span roughly 15° and river — even with a goal in mind, you
many others, is to map the sky in search 30°, respectively, and they both have often have little idea of what lies ahead,
of these stars. arms that extend far beyond that. other than almost certain adventure.

Charting the nearby It has been 22 years since I first saw Acknowledgements
southern sky the Magellanic Clouds with my own
eyes. Since then, I’ve learned just how I dedicate this article to Paul
One of the best instruments for map- closely connected they are to so many Hodge, my trusty guide to graduate
ping large areas of southern sky is the astronomical discoveries. But, even more school, the Magellanic Clouds,
Dark Energy Camera, or DECam, which importantly, I’ve realized they still hide astronomy, and the Cascades. He
is also mounted on the Blanco telescope many surprises. was exceptional in his kindness,
at CTIO. This instrument has a field humility, intelligence, and curiosity,
of view 4.5 times wider than the Full When I gaze at them now, I imagine and I miss him deeply. I thank all
Moon and was built to conduct the what they might have looked like over of my collaborators and colleagues,
Dark Energy Survey (DES), which aims their lifetimes: a pair of galaxies, con- who have made this astronomical
to measure the properties of dark energy, densed from gas settling onto lumps of adventure fun and exhilarating.
as well as chart the halo of the Milky dark matter, dancing around each other
Way and explore the outskirts of the Knut Olsen is an astronomer at the Optical-
Magellanic Clouds. Infrared Astronomy Research Laboratory. He
now lives in Tucson, Arizona, but will always
In 2015, two groups — one led by remember his time under the southern sky.
astrophysicist Keith Bechtol of the

WWW.ASTRONOMY.COM 23

HOW

GALILEO

blended science and art
Always drawing, sketching, or painting, Galileo Galilei
saw the cosmos through an artist’s eye. BY DAN FALK

GALILEO GALILEI (1564–1642) Earthshine occurs when sunlight reflecting off Earth on the remarkable object, speculating on
illuminates the portion of the Moon still in shadow. its significance.
is often recognized as the founder of Galileo ultimately — correctly — concluded this was
modern physics, perhaps even the father the source of what he called the Moon’s “secondary Galileo was teaching mathematics at
of modern science itself. But this popu- light.” This image, taken from New South Wales, the University of Padua in 1609 when he
lar image neglects one important facet Australia, shows the daylight side of the Moon learned of a curious optical device from
of his Renaissance personality: Galileo illuminated directly by the Sun at right, with Holland that was said to make distant
the artist. earthshine illuminating the nighttime portion objects appear as if they were much
of the Moon at left. DYLAN O’DONNELL closer. Improving on the original Dutch
Art and science have always been invention, Galileo made a device that
intertwined, and Galileo exemplified from an early age. By the 1590s, he was could magnify 20 or even 30 times. In
how they can inspire and inform one already drawn to the Copernican model the fall of 1609 and the winter of 1610,
another. In addition to being a skilled of the heavens, in which the Sun, rather he aimed this instrument at the night
observer and a keen thinker, he was a than Earth, is recognized as the center sky and made a series of jaw-dropping
talented artist, trained in cutting-edge of our system of planets. When a new discoveries. With his telescope, he
perspective techniques pioneered by his star appeared in the sky in 1604 — the observed that the Moon has an irregular
fellow Italian artists. His artistic sensi- supernova now known as Kepler’s Star surface peppered with mountains, cra-
bility played a key role in his scientific — Galileo delivered a series of lectures ters, and flat plains; that the Milky Way
insights, leading some 400 years ago is made up of thousands of stars too
to a new picture of the universe. faint to see with the unaided eye; and
that Jupiter is accompanied by four
A MAN OF SCIENCE “stars” seemingly in orbit around the
great planet. All of these are recounted
Galileo is remembered first and fore- in Sidereus Nuncius (Starry Messenger),
most as a scientist. His father was a which Galileo published in March 1610.
skilled musician, teacher, and music He would later analyze sunspots and
theorist who produced several surviv- discover that Venus, like the Moon,
ing compositions. Galileo’s mother was displays distinct phases.
an educated woman from a well-to-do
family who could claim a cardinal Physics also commanded Galileo’s
among her relatives. In 1581, the young attention. Throughout his life, he stud-
Galileo set off to Pisa to study medicine ied motion — especially accelerated
— more to satisfy his father’s desires motion — by experimenting with falling
than his own. It soon became clear that bodies and by rolling objects down
his real interest was in mathematics; he inclined planes. He also studied what
had also been interested in astronomy

24 ASTRONOMY • NOVEMBER 2020

Galileo Galilei was not only a man of science,
but also an accomplished artist with a keen
eye. Historians speculate his talent for art
ultimately helped him decipher the physical
reality of the objects he observed. GALILEO GALILEI

(1564-1642). OIL PAINTING AFTER JUSTUS SUSTERMANS, 1635. COURTESY OF

THE WELLCOME COLLECTION, ATTRIBUTION 4.0 INTERNATIONAL (CC BY 4.0)

ABOVE: This line engraving of Galileo depicts the
astronomer alongside a drawing that shows Earth’s
orbit around the Sun, as well as the Moon’s orbit
around Earth. GALILEO GALILEI. LINE ENGRAVING BY BOUTROIS &

JOUANNIN AFTER J. A. LAURENT, 1822. COURTESY OF THE WELLCOME COLLECTION,

ATTRIBUTION 4.0 INTERNATIONAL (CC BY 4.0)

RIGHT: Galileo turned his telescope on familiar
constellations, including Orion (left). With the aid of
greater magnification, he identified numerous “new”
stars (drawn as small star shapes) amidst the
previously known naked-eye stars (depicted with
larger star-shaped outlines) of the Hunter’s belt and
sword. Similarly, he identified many new stars
among the familiar luminaries of the Pleiades (right).

GALILEI, GALILEO. SIDEREUS NUNCIUS. APUD THOMAM BAGLIONUM, 1610.

COURTESY OF THE SMITHSONIAN LIBRARIES (HTTPS://DOI.ORG/10.5479/

SIL.95438.39088015628597)

we now call inertia, investigated the Galileo also appears to have struck being very interested in the arts and
strengths of various materials, and devel- up lasting friendships with some of the in visual representation in general.”
oped the modern science of mechanics. leading artists of his day. They often
sought out his opinions, recognizing his SCIENCE THROUGH ART
All of these facts paint the traditional skill as a draftsman and as a master of
picture of “Galileo the scientist.” But he perspective. Galileo collected paintings This specialized knowledge paid off
was also a skilled artist, drawing in part and loaned money to artists, as well. “He when Galileo first aimed his telescope
from knowledge that he acquired at the really thought of himself as being deeply at the Moon, although he initially strug-
Accademia delle Arti del Disegno involved in the art world,” says Eileen gled to interpret what he saw. While light
(Florentine Design Academy), where Reeves, a professor of comparative litera- and dark areas on the Moon are visible
painters, sculptors, and architects gath- ture at Princeton University and the to the naked eye, his telescope revealed
ered to discuss the intricacies of their author of Painting the Heavens: Art and what appeared to be mountains and val-
profession. Galileo is believed to have Science in the Age of Galileo (Princeton leys. But how could he be sure? After
studied there in 1585 and was elected to University Press, 1997). “I see Galileo as all, he was viewing them from above, as
its membership in 1613. At the Academy, well as from about a quarter of a million
he would have been exposed to key ideas
such as linear perspective — the tech-
nique employed by artists to render
objects in three dimensions, developed a
century earlier by the architect and
designer Filippo Brunelleschi (1377–
1446). Artist and polymath Leon
Battista Alberti (1404–72) had produced
two lavishly illustrated treatises in
which he expounded on the importance
of realism and three-dimensionality; it’s
likely that Galileo absorbed these ideas.

26 ASTRONOMY • NOVEMBER 2020

ABOVE: These engravings of the Moon (top), based
on Galileo’s wash drawings, show a crater on the
terminator larger than any that truly exists. It may be
the crater Albategnius (indicated by an arrow on the
bottom photo), clearly embellished by Galileo or his
engraver. GALILEI, GALILEO. SIDEREUS NUNCIUS. APUD THOMAM BAGLIONUM,

1610. COURTESY OF THE SMITHSONIAN LIBRARIES (HTTPS://DOI.ORG/10.5479/

SIL.95438.39088015628597); NASA’S SCIENTIFIC VISUALIZATION STUDIO

miles (384,400 kilometers) away. So, he observed the play of sunlight on those One likely source of inspiration for
sketched what he saw and tried to make lunar mountains, Galileo was reminded these insights was a book by Daniele
sense of it. “He must have drawn on the of familiar sights on our own planet. As Barbaro called La Pratica della
tricks of perspective that he had learned he wrote in Sidereus Nuncius, “There is a Perspettiva, published in 1569. It con-
years before,” says Reeves. For Galileo, similar sight on earth about sunrise, tained, among other things, lessons on
“drawing was a means of discovery, a when we behold the valleys not yet how to draw spheres — not only per-
form of thinking.” flooded with light though the mountains fectly smooth spheres, but also spheres
surrounding them are already ablaze with various protuberances. Another
Galileo paid particular attention to with glowing splendor on the side oppo- book, Lorenzo Sirigatti’s La Pratica di
the features visible along the terminator, site the sun. And just as the shadows in Prospettiva, published in 1596, contained
the line that divides the light and dark the hollows on earth diminish in size as similar practical instructions. Galileo
parts of the Moon. He noticed how the the sun rises higher, so these spots on also sat in on lessons on Euclidean
peaks of mountains on the dark side the moon lose their blackness as the illu- geometry taught by the Florentine math-
are lit up first, with the sunlight slowly minated region grows larger and larger.” ematician Ostilio Ricci (1540–1603).
making its way down their sides. As he

WWW.ASTRONOMY.COM 27

These innovations certainly helped LEFT: References such are “artistically superb.” Galileo’s skill at
artists render the world around them as Lorenzo Sirigatti’s applying the wash, carefully revealing
more vividly — but some scholars argue La Pratica di Prospettiva, the paper below only in specific areas,
they also could have helped pave the way a page from which is required enormous talent, Olson says.
for the Scientific Revolution itself. Writing shown here, guided “Only a very highly trained and sophisti-
in Art Journal in 1984, Samuel Edgerton, Galileo’s understanding cated artist would know how to do that.”
an emeritus professor of art history at of perspective. Such
Williams College in Massachusetts, books taught how to Edgerton, too, has praised the artistic
claimed there is “a clear case of cause and draw geometric shapes nature of Galileo’s lunar sketches. In his
effect between the practice of Italian with various surface book The Heritage of Giotto’s Astronomy
Renaissance art and the development of features. This (Cornell University Press, 1991), he writes:
modern experimental science.” Edgerton, knowledge likely helped “With the deft brushstrokes of a practiced
now 94, says he “absolutely” stands by Galileo understand that watercolorist, he laid on a half-dozen
that assessment more than 30 years later. he was looking down at grades of washes, imparting to his images
The key, he says, was the discovery of the mountains and crater an attractive soft and luminescent
idea of “viewpoint” by Renaissance art- walls on the Moon. quality.” Galileo’s use of an “almost
ists. When we look at a set of railway impressionistic technique” in rendering
tracks converging toward the horizon, the ARTOKOLORO/ALAMY STOCK PHOTO lighting effects “reminds us of Constable
convergence is not a property of the tracks and Turner, and perhaps even Monet.”
(which are, after all, parallel), but a prop- RIGHT: Galileo made
erty of our minds. The effect “is in your these watercolors from Interestingly, the published drawings
head and in your eyes,” Edgerton says, observations of the that appear in Sidereus Nuncius are quite
“and the artists knew that.” Moon through his different from the wash drawings. Most
telescope in late 1609. obviously, a gigantic crater larger than
And only someone as skilled as They are the first any that actually exists on the Moon’s
Galileo could see that mountains on the realistic depictions of surface figures prominently on the
Moon were just like the mountains here the Moon ever created, Moon’s terminator as depicted at First
on Earth — once he understood the view- and later served as a Quarter or Last Quarter. (The closest
point from which they were being seen. basis for the engravings real-life candidate for this oversized fea-
in Sidereus Nuncius, ture is a medium-sized crater known as
although the engraver Albategnius; however, either Galileo or
likely took some artistic his engraver seems to have embellished it
liberties. FIRENZE, BNC, almost beyond recognition.) Historians
speculate that Galileo gave his drawings
GALILEIANO 48, F. 28R; BY PERMISSION to the engraver as a guide but also
encouraged him to employ his artistic
OF MINISTERO PER I BENI E LE license, exaggerating certain features
to support the accompanying text.
ATTIVITÀ CULTURALI E PER IL
IN ANOTHER LIGHT
TURISMO/BIBLIOTECA NAZIONALE
Another phenomenon that challenged
CENTRALE DI FIRENZE. THIS IMAGE Galileo as both an artist and a scientist
was earthshine — the faint illumina-
CANNOT BE REPRODUCED WITHOUT tion of the dark part of the Moon’s face
caused by light from the Sun reflecting
PERMISSION FROM THE NATIONAL off of Earth. It is most readily seen in the
first few days following New Moon. In
LIBRARY OF FLORENCE. Galileo’s time, this ghostly shine, which
he referred to as the Moon’s “secondary
A TRAINED ARTIST light,” was far more mysterious.

Galileo’s depiction of the lunar surface, As he described it in Sidereus Nuncius,
as rendered in a series of engravings, “When the moon is not far from the sun,
are one of the highlights of Sidereus just before or after new moon, its globe
Nuncius. Instead of the perfect Moon offers itself to view not only on the side
imagined by the ancients, we see the where it is adorned with shining horns,
rugged, pockmarked Moon that we but a certain faint light is also seen to
know today. The book’s engravings were mark out the periphery of the dark part
preceded by a series of wash drawings which faces away from the sun … This
— paintings made with a technique in remarkable gleam has afforded no small
which brown ink is diluted in water so perplexity to philosophers.”
the brushstrokes are nearly invisible,
often allowing the underlying paper or
canvas to be seen. These drawings, along
with some of Galileo’s original note-
books, are now housed in the Biblioteca
Nazionale Centrale in Florence.
Astronomers and historians agree that
the drawings are based on observa-
tions of the Moon carried out between
November 30 and December 18, 1609.

The wash drawings are more than just
instructions for the engraver — they are
works of art in their own right, says
Roberta Olson, an art historian and
Curator of Drawings at the New York
Historical Society. She describes the wash
drawings as “illusionistic studies” that

28 ASTRONOMY • NOVEMBER 2020



Galileo published Sidereus Nuncius, whose title page appears here, in 1610. The With his telescope, Galileo observed four “stars” that appeared to orbit the
book contained results of his telescopic observations of the skies and included planet Jupiter. In reality, these are moons: Io, Europa, Ganymede, and Callisto.
drawings of the Moon, star clusters, constellations, and Jupiter’s four largest Sidereus Nuncius contains numerous pages of observations showing the moons
moons, later christened the Galilean moons. GALILEI, GALILEO. SIDEREUS NUNCIUS. APUD THOMAM in various configurations around the gas giant. GALILEI, GALILEO. SIDEREUS NUNCIUS. APUD

BAGLIONUM, 1610. COURTESY OF THE SMITHSONIAN LIBRARIES (HTTPS://DOI.ORG/10.5479/SIL.95438.39088015628597) THOMAM BAGLIONUM, 1610. COURTESY OF THE SMITHSONIAN LIBRARIES (HTTPS://DOI.ORG/10.5479/SIL.95438.39088015628597)

Galileo eventually concluded that the bodies that appeared to change their IN GOOD COMPANY
phenomenon originates in light reflected positions from night to night, but always
from our own planet, and again, his remained close to the planet itself. The Evidence that artists held Galileo in the
interpretation may have leaned on his only reasonable conclusion was that highest regard can be found in a paint-
artistic knowledge. The principles of these were moons revolving around ing by the Flemish artist Peter Paul
reflected light were already quite famil- Jupiter. But his notebooks reveal that he Rubens. In his Self Portrait in a Circle of
iar to artists. Edgerton points out that was struggling to make sense of what he Friends from Mantua, dating from about
Alberti offered a description of the phe- was seeing. For starters, the moons 1604, we see six figures: Rubens; his
nomenon not for the Moon specifically, didn’t always appear in a straight line. brother; the son of a merchant; the son
but in terms of general principles, in his “At first, Galileo ‘corrects’ his drawings,” of a nobleman; a Flemish scholar; and a
treatise Della Pittura (On Painting). says Reeves. “He figures they should be young man near the center of the canvas,
Alberti noted that the “reflection of rays lined up.” But eventually, Galileo con- pegged by some historians as Galileo.
always takes place at equal angles” and cluded that the moons’ orbits around We know that Galileo was friendly with
that such rays “assume the color they Jupiter must be inclined to our line both Rubens and his brother and that
find on the surface from which they of sight, and drew the moons as they “they probably shared similar philosoph-
are reflected. We see this happen when actually appear in the sky. ical ideas,” says Reeves. It’s also possible
the faces of people walking about in that they shared the Copernican view of
meadows appear to have a greenish Galileo was always drawing, sketch- the cosmos, though this is much harder
tinge.” Artists had long applied Alberti’s ing, and painting. “I think he found it to prove. If they did, however, then this
logic to depicting terrestrial objects, but hard to think without drawing,” Reeves intriguing painting could be “a sly way
Galileo may have been the first to apply says. If he was unsure how something of doing it,” without overtly identifying
it to the heavens. ought to be treated, he would ask his oneself as a Copernican, she says.
artist friends — and they would likely
Galileo faced a very different chal- consult him, too. This back-and-forth Artists were also inspired by Galileo’s
lenge when he aimed his telescope at the “was a constant process with Galileo, astronomical discoveries. Most notable
great planet Jupiter. He saw four small and with his friends.” is the painter Lodovico Cardi, better
known as Cigoli (1559-1613). Cigoli’s most

30 ASTRONOMY • NOVEMBER 2020

important commission came when he was In his Immacolata fresco adorning the Basilica di
asked to paint the chapel of Pope Paul V in Santa Maria Maggiore in Rome, Cigoli painted the
the Basilica of Santa Maria Maggiore in Moon beneath the Virgin Mary’s feet as it appeared
Rome. He began the work that would adorn through his friend Galileo’s telescope. Previous
the inside of the cupola, often called the paintings with similar imagery depicted our satellite as
Immacolata, in September of 1610, and com- smooth and featureless, rather than its true pockmarked
pleted it by 1612. The biblical scene it depicts, and cratered form. LIVIOANDRONICO2013/WIKIMEDIA COMMONS
based on the book of Revelation, shows the
Virgin Mary as the Queen of Heaven stand- Flemish artist Peter Paul
ing on the Moon, wearing a multicolored Rubens completed Self
robe and carrying a scepter in her right Portrait in a Circle of Friends
hand. A halo of 12 stars looms above her from Mantua around 1604.
head; at the bottom we see a coiled serpent. In addition to himself, seen
looking toward the viewer,
The fresco’s most striking feature is the Rubens painted his brother,
lunar surface, clearly pockmarked with the sons of a merchant and
craterlike features. Scholars have concluded a nobleman, and a Flemish
that Cigoli’s depiction of the Moon is scholar. Some historians
directly indebted to one of the lunar images identify the sixth figure —
published in Sidereus Nuncius, in which the the bearded man, third from
Moon is seen at its First Quarter phase. But the left, with the prominent
it is also possible that Cigoli made his own white collar — as Galileo.
observations, perhaps peering through one
of Galileo’s telescopes. “I would think that RUBENS, PETER PAUL; SELF PORTRAIT IN A
[Cigoli] had, at the very least, access to a CIRCLE OF FRIENDS FROM MANTUA,
telescope,” says Reeves. WALLRAF-RICHARTZ-MUSEUM & FONDATION
CORBOUD (DEP. 0248, KÖLN). RHEINISCHES
Interestingly, while the traditional BILDARCHIV KÖLN, WALZ, SABRINA,
Aristotelian view of the Moon was RBA_D038880
that of an unblemished, perfectly
spherical body, Cigoli appears to WWW.ASTRONOMY.COM 31
have had no hesitation in
depicting it as irregular and
mountainous, just as Galileo
had. While Galileo would be
hauled before the Inquisition
some 20 years later in 1633 —
in part for his vocal support of
Copernican astronomy — the
Catholic authorities do not seem
to have been particularly bothered
by Cigoli’s bold depiction of the Moon.

Clearly, Galileo was much more than
a single-minded man of science; rather, he
was a polymath with artistic leanings that
deserve greater attention. Those artistic
skills helped him beyond measure as he
struggled to comprehend the sights revealed
by his telescope and to communicate those
sights to a mass audience.

“It was all about discovery,” says Olson.
“Discovery of the physical world, discovery
of the principles that make it work.” The
scientists of Galileo’s day, as well as the
artists, wanted “to see how the cosmos
worked.”

Dan Falk (@danfalk) is a science journalist
based in Toronto. His books include The
Science of Shakespeare and In Search of Time.

SKY THIS MONTH Visible to the naked eye
Visible with binoculars
THE SOLAR SYSTEM’S CHANGING LANDSCAPE AS IT APPEARS IN EARTH’S SKY. Visible with a telescope
BY MARTIN RATCLIFFE AND ALISTER LING

NOVEMBER 2020 A spectacular fireball lights up the Michigan sky in this 2018 shot. Fast-moving Leonid meteors
may leave similar trains of ionized gas in the sky when the shower peaks this month. TONY HEBERT
Planets
shine
morning
and night

With the seven major through increasingly more of month only 2.3° apart. The pair dims by 0.1 magnitude in one
planets on display, our atmosphere. Refraction makes a stunning spectacle in week. The disk spans 37" and
this month is a busy time for worsens, too, causing color binoculars. Mount them on a shrinks to 34" by November 30,
observers. Jupiter and Saturn fringes around the planets. tripod and soak in the sight. as the planet’s distance from
continue their dramatic pairing Some of Jupiter’s moons are Earth increases. November
in the southern sky. Mars Jupiter and Saturn start visible in binoculars as well. opens with a fine transit of
remains near its peak and November 5.1° apart. Both have Ganymede’s shadow underway.
begins its retreat from Earth; resumed direct easterly motion A waxing crescent Moon Not long after the moon’s
catch it early in the month while relative to the background stars. stands west and then east below shadow makes it halfway across
you can. Neptune is near a By virtue of being closer, Jupiter the duo on November 18 and the disk, Io reappears from
bright star, while Uranus appears to move more quickly 19, respectively. Jupiter’s huge shadow. Watch
remains in a sparse region of than Saturn, catching up with the empty space some 20" from
sky and is up all night. The the ringed planet. They end the Jupiter is a spectacular mag- Jupiter’s eastern limb for Io’s
predawn sky hosts Venus and nitude –2.2 on November 1 and reappearance at 7:43 P.M. EST.
Mercury, a treat for early risers. Ganymede’s shadow leaves
The window for observing Bright lights before sunrise Jupiter’s face at 9:06 P.M. EST.
Jupiter and Saturn is narrowing. There are several more transits
In early November, the planets Arcturus Porrima and occultations in the first half
set an hour before midnight. BOÖTES of November, but progressively
Four weeks later, they’re gone by VIRGO fewer throughout the month.
9:30 P.M. local time. The longer
nights afford an early start — Venus Saturn sits east of Jupiter,
the best time to begin observing shining at magnitude 0.6. At
is as soon as twilight starts and Moon Spica nearly twice the distance of
the Sun has gone down. Jupiter, Saturn’s disk — in
On November 1, when day- Mercury 10° reality comparable in size to
light saving time ends, you can Jupiter’s — appears half the
begin at 5:30 P.M. Jupiter and November 13, 1 hour before sunrise size in our telescopes: 16".
Saturn stand 27° and 29° high, Looking east
respectively, in the south. Catch Saturn’s atmospheric features
them early because at lower A thin crescent Moon joins planets Mercury and Venus in Virgo the morning are more subtle than Jupiter’s.
altitudes, their light passes of November 13. Virgo’s bright alpha star, Spica, shines nearby. ALL ILLUSTRATIONS: Use a good-quality eyepiece
with well-corrected color trans-
ASTRONOMY: ROEN KELLY mission to see subtle details.

32 ASTRONOMY • NOVEMBER 2020

RISING MOON I Swinging between opposites

GLIDING QUIETLY across the solar system’s Byrgius A
dance floor is the endearing couple of Terra and

OBSERVING Luna. From our earthly perspective, the latter N
HIGHLIGHT appears to circle us, at times leading and other E
times following. But our Moon never actually
VENUS, MERCURY, and the moves backward relative to the audience of Byrgius
stars. We simply elegantly swap places while
crescent Moon share the always moving forward around the broad circle
November 13 predawn sky. The we call the ecliptic.
trio hangs near the bright star
Concentrate on Luna’s face to notice its
Spica in Virgo. monthly rise and dip. In the far southwest (lower

left for observers north of the equator), Byrgius A A
is small impact crater surrounded by a bright

apron and rays, quite prominent in binoculars.

(The same goes for Jupiter.) The From night to night immediately following
the Full Moon on Halloween, this dazzling

northern side of Saturn’s rings dimple lifts to the upper right as Luna

is tilted toward us by 22°. This rises slightly “above” us in its orbit, Watching the small impact crater
value diminishes over the next which is tilted 5.1° to the ecliptic. Byrgius A can easily illustrate the
few years until the next ring Moon’s orbit around Earth. CONSOLIDATED
plane crossing in 2025. During the passage through
New Moon, we swap places. Arriving at LUNAR ATLAS/UA/LPL; INSET: NASA/GSFC/ASU
Titan shines at 8th magni- First Quarter, we find ourselves leading while
tude. It is due north of Saturn peering “down” at Luna in the bottom of its dip. last nights of the month. The remaining two dark
November 3 and 20, and due With binoculars on the 25th or 26th, look for a spots are tucked right against the limb when we
south of Saturn November 11 trio of dark spots at the upper right of its face: reach Full phase on the 30th. In December, you
and 27. Look also for a trio of Lacus Spei, Endymion, and, at the very edge, can watch the dimple of Byrgius A climb up from
fainter, 10th-magnitude moons Mare Humboldtianum. (See last month’s “Rising the lower left once again.
closer in: Tethys, Dione, and Moon” for more details on this region.)
Rhea. Closer to the rings’ edge We've come back face-to-face, relative to
is 12th-magnitude Enceladus. With each step toward Full, Luna spins a bit the spotlight of our Sun, but Luna's graceful
too fast while rising. As a result, that trio of spin, rise, and dip combination does not repeat
Iapetus reaches greatest braids rotates to the upper right and Mare exactly. That grander cycle takes some 18 years,
western elongation November 4. Humboldtianum disappears from view in the a saros, to complete.

This is the brightest Iapetus can

appear, glowing near magni- METEOR WATCH I A lion of a shower
tude 10.2, 8' due west of Saturn.
The moon dims to near magni-

tude 11 as it swings to superior Leonid meteor shower THE LEONID METEOR SHOWER
conjunction on November 25.

November evenings are a Denebola Radiant LEO Castor is active between November 6
great time to try imaging dwarf and 30, peaking the morning of
planets. Pluto is in the southern Pollux November 17 with a projected
sky near Jupiter, Ceres is in the GEMINI zenithal hourly rate of 15 meteors
south, and Eris is in the east. per hour. It’s a favorable year with
Regulus Betelgeuse the Moon out of the way.

Pluto shines near 15th mag- CANIS ORION Meteor rates increase as the
nitude in Sagittarius and is a Procyon MINOR radiant climbs higher, so early
morning hours from 3 A.M. to 6 A.M.
mere 41' due south of Jupiter on Alphard Sirius Rigel offer the best views. The Leonids
November 12. A one-minute CANIS LEPUS produce fast-moving meteors,
guided exposure through an MAJOR many of which show persistent
80mm refractor should catch it. trains — luminous trails of ionized
Ceres is a binocular object at HYDRA gas that can take many seconds to
fade away. Sometimes trains are
magnitude 8.7. Find it in south- caught by high-level winds, produc-
ing intriguing shapes. The Leonid
ern Aquarius all month. You’ll 10° meteor shower is associated with
Comet 55P/Tempel-Tuttle, which
want to catch Ceres as it LEONID METEORS November 17, 5 A.M. last reached perihelion in 1998.
cruises within 1° of the Looking south
Helix Nebula (NGC 7293) Active dates: November 6–30 WWW.ASTRONOMY.COM 33
between November 18 and Peak: November 17 The Leonids’ radiant lies in the sickle of
24. Eris is a challenge Moon at peak: Waxing crescent Leo the Lion, which rises shortly after
Maximum rate at peak: midnight. Wait a few more hours for the
— Continued on page 38 greatest meteor rates.
15 meteors/hour

STAR DOME N

_

HOW TO USE THIS MAP M82 k _
M81
This map portrays the sky as seen
near 35° north latitude. Located NE
inside the border are the cardinal
directions and their intermediate a
points. To find stars, hold the map `
overhead and orient it so one of
the labels matches the direction LYNX _ Polaris
you’re facing. The stars above NCP
the map’s horizon now match E M _
what’s in the sky. URSA
CA MINOR
The all-sky map shows
how the sky looks at: e _c Capella D R PA `
d
9 P.M. November 1 L A LO ` b
8 P.M. November 15 ` CEPHEUS a
7 P.M. November 30 MM3368AU R I G A S I

Planets are shown d M35 M37 `
at midmonth
¡ C

N¡GCNG86C9884 d P a I S ` `

M1 b Algol l a b O AS +c b d
c _ f
EIA
f P _

¡ E L A C E RTA
eb
R

S _

E A N D R O M E DA ` M33
a
U

S

c Pleiades TR _
d
`

/ I

ORION A

ha _ N k
Aldebaran
MAP SYMBOLS TAU R U S ` M31

Open cluster ¡h GU
Globular cluster
Diffuse nebula L
Planetary nebula
Galaxy U

STAR E M
MAGNITUDES
ARIES _ b _ `
Sirius Uranus _ +d
0.0 3.0
1.0 4.0 `
2.0 5.0 a

d PEGASUS

i PISCES

a_ ¡

_ c

_ Mars Path of a e
a k Mira (ecliptic)A
the Sun R I U S _

b Q U A

a ERIDANUS

d

CETUS b

o

STAR COLORS _ FORNAX `
SGP NGC 253
A star’s color depends _ Fomalhaut
on its surface temperature. _
SE PIS CIS
The hottest stars shine blue SCULPTOR AU STR

•• Slightly cooler stars appear white I N
• Intermediate stars (like the Sun) glow yellow
• Lower-temperature stars appear orange a _ PHOENIX GRU
• The coolest stars glow red `
• Fainter stars can’t excite our eyes’ color `

receptors, so they appear white unless you
use optical aid to gather more light

S

BEGINNERS: WATCH A VIDEO ABOUT HOW TO READ A STAR CHART AT
www.Astronomy.com/starchart.

NOVEMBER 2020 SAT.

SUN. MON. TUES. WED. THURS. FRI.

a HERCULES d 1 234567 ILLUSTRATIONS BY ASTRONOMY: ROEN KELLY

`i / M13 NW 8 9 10 11 12 13 14
c
c 15 16 17 18 19 20 21
d
22 23 24 25 26 27 28
DRAC
29 30
f
Note: Moon phases in the calendar vary in size due to the distance
b from Earth and are shown at 0h Universal Time.

¡ Vega + CALENDAR OF EVENTS
_
r d CYGNUS ` 1 Asteroid Flora is at opposition, 2 A.M. EST
De 3 Mercury is stationary, 3 A.M. EST
b LY R A 8 Asteroid Juno is in conjunction with the Sun, 4 A.M. EST

`a M57 Last Quarter Moon occurs at 8:46 A.M. EST
_ 10 Mercury is at greatest western elongation (19°), noon EST
_ VULPECULA 12 The Moon passes 3° north of Venus, 4 P.M. EST
a 13 The Moon passes 1.7° north of Mercury, 4 P.M. EST
14 The Moon is at perigee (222,350 miles from Earth), 6:43 A.M. EST
c M27 W 15 New Moon occurs at 12:07 A.M. EST
¡
Venus passes 4° north of Spica, 8 A.M. EST
Enif M15 `_ DELPHINUS a ` _a b AQUILA c Mars is stationary, 2 P.M. EST
Altair S A G I T TA 17 Leonid meteor shower peaks
EQUULEUS d _ 19 The Moon passes 2° south of Jupiter, 4 A.M. EST
The Moon passes 3° south of Saturn, 10 A.M. EST
_ h 21 First Quarter Moon occurs at 11:45 P.M. EST
23 The Moon passes 5° south of Neptune, 7 A.M. EST
e M11 25 The Moon passes 5° south of Mars, 3 P.M. EST
UM 26 The Moon is at apogee (252,211 miles from Earth), 7:29 P.M. EST
S 27 The Moon passes 3° south of Uranus, noon EST
29 Neptune is stationary, 4 A.M. EST
U T 30 Full Moon occurs at 4:30 A.M. EST; penumbral lunar eclipse

N U

` R C

O S

C

I

PR

_

A

C

` Saturn
Jupiter
a
b

NUS MICROSCOPIUM SW

a

US

WWW.ASTRONOMY.COM 35

PATHS OF THE PLANETS

UMa LMi AUR
CVn
BOÖ GEM
CrB TRI

COM ARI

SER LEO Eunomia Psyche TAU Uranus
Vesta CNC ORI PSC
Sun
LIB Path of the Moon (ecliptic) CMi Mars
Path of the Sun
Mercury shines VIR SEX MON Parthenope
brightly before dawn Venus Papagena
CRV CRT
in mid-NovLeUmPber CET

H YA Asteroid Flora reaches
LEP opposition November 1
CMa
ERI FOR
SCL

ANT PYX
VEL
PUP COL CAE PHE

CEN

Dawn Midnight

Moon phases

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

To locate the Moon in the sky, draw a line from the phase shown 30 29 28 27 26 25
for the day straight up to the curved blue line.

THE PLANETS Uranus THE PLANETS IN THE SKY
IN THEIR ORBITS
Jupiter Neptune These illustrations show the size, phase,
Arrows show the inner Saturn and orientation of each planet and the two
planets’ monthly motions brightest dwarf planets at 0h UT for the dates
and dots depict the in the data table at bottom. South is at the top
outer planets’ positions to match the view through a telescope.
at midmonth from high
above their orbits.

Mars

Venus

Mercury

Pluto

Mercury PLANETS MERCURY VENUS
Greatest western elongation
Date Nov. 15 Nov. 15
is November 10 Magnitude –0.7 –3.9
Angular size 6.1" 12.4"
Earth Illumination 73% 85%
Distance (AU) from Earth 1.101 1.350
Mars Distance (AU) from Sun 0.351 0.719
Right ascension (2000.0)
Venus Declination (2000.0) 14h12.1m 13h22.6m
–11°00' –6°47'
Ceres

Jupiter

36 ASTRONOMY • NOVEMBER 2020

This map unfolds the entire night sky from sunset (at right) until sunrise (at left). Arrows NOVEMBER 2020
and colored dots show motions and locations of solar system objects during the month.

CYG LYR HER BOÖ Callisto 1
2
VUL CrB Europa 3
DEL SGE 4
PEG Io
5 Jupiter
EQU AQL SER OPH SER Ganymede Ganymede
Sun 6 Callisto
Celestial equator SCO JUPITER’S 7
ARA LUP MOONS 8
Neptune VIR 9
Dots display 10
AQR Saturn Jupiter SCT positions of
Galilean satellites 11 Europa
Ceres Pluto at 8 P.M. EST on
the date shown. 12
CAP South is at the
top to match the 13 Io
PsA Comet 88P/Howell view through a
GRU CRA telescope. 14
15
TEL 16
17
Early evening 18
19
24 23 22 21 20 19 18 17 16 15 14 20
21
Jupiter Saturn S 22
Ceres WE 23
24
N 25
26
10" 27
28
Uranus Neptune Pluto 29
30
MARS CERES JUPITER SATURN URANUS NEPTUNE PLUTO

Nov. 15 Nov. 15 Nov. 15 Nov. 15 Nov. 15 Nov. 15 Nov. 15
–1.7 8.9 –2.1 0.6 5.7 7.9 14.8
17.5" 0.5" 35.6" 16.0" 3.7" 2.3" 0.1"
95% 97% 99% 100% 100%
0.536 2.677 5.532 100% 100%
1.450 2.972 5.112 10.388 18.821 29.494 34.647
9.994 19.778 29.928 34.161
0h56.4m 22h27.9m 19h39.3m 19h55.7m 2h22.4m 23h17.3m 19h38.5m
5°06' –22°17' –21°56' –21°08' 13°40' –5°47' –22°40'

WHEN TO

SKY THIS MONTH — Continued from page 33 VIEW THE

Saturn’s small moons get in line east-northeast of Phi. Shining PLANETS

at magnitude 7.9, a pair of 7x50 EVENING SKY

Titan S Enceladus, Tethys, binoculars will snag it. With a Mars (east)

and Dione line wider field of view, you’ll notice Jupiter (south)
up east of Saturn two 6th-magnitude stars form- Saturn (south)
the night of ing a triangle with Phi; they’re Uranus (east)
November 27, located twice as far from Neptune (southeast)
while Rhea stands
due north of Dione. MIDNIGHT
Only moons glowing the star as the planet, with

W Enceladus at magnitude 11 and Neptune in the center of the Mars (southwest)
Tethys brighter are shown. triangle. A telescope will reveal Uranus (southwest)
its bluish disk, spanning 2".
Dione Neptune (west)

Saturn Rhea Uranus is only one day past MORNING SKY
opposition on November 1 and Mercury (east)

visible all night at magnitude Venus (east)
30" 5.7. It lies in a bland region Uranus (west)

November 27, 10 P.M. EST Iapetus 10.5° southeast of Hamal, Aries’
brightest star. With binoculars,

follow a meandering line of horizon. On November 1, it

reserved for larger telescopes the 4th-magnitude star 5th-magnitude stars until you rises among the stars of Virgo

(14 inches or greater) and lon- Phi (ϕ) Aquarii all month reach 19 Arietis. Uranus stands the Maiden nearly three hours

ger exposures with a camera. If long. If you can center the 3° southeast of this star on before the Sun. Mercury rises

you can reach magnitude 19, bright star in binoculars, you’re November 1. The gap shrinks later, 20° farther east along the

give it a shot. It lies about 12° also looking at Neptune. The to 2.5° by November 30. A ecliptic. The two planets main-

southeast of Mars in a bland ice giant drifts westward telescope reveals a bluish-green tain their social distance dur-

region of sky 2° due north of a against the starry background 4"-wide disk. ing November.

5th-magnitude field star, until November 29, when it Soon after 4 A.M. local time, Venus is a bright magnitude

HIP 7999, in northern Cetus. reaches its stationary point 44' Venus appears above the eastern –4. Grab a pair of binoculars

Mars is stunning, high in

the east an hour after sunset. It COMET SEARCH I A fuzzy familiar
stands out at magnitude –2.1,

equivalent to Jupiter’s glow, in

the dim constellation Pisces THE EARLY EVENING COMET Comet 88P/Howell
the Fish. Now a few weeks past CRUISE continues. Unlike the

its mid-October opposition, narrow loops of most icy visitors, Algedi N
Mars continues westward Comet 88P/Howell’s 5.5-year orbit i
for half the month, halting is nestled between that of Mars

against the background stars and Jupiter. Like Mars after oppo- ` p

November 15 before resuming sition, it runs on the racetrack just c l1 l2
its eastward direct motion. outside ours, barely losing speed.
As a bonus for northerners, CAPRICORNUS M75 Saturn SAGIT TARIUS / j1
As Mars recedes from Howell climbs higher in the sky, E k j2
Earth, its brightness dips, thanks to Earth’s tilt. Jupiter Pluto
reaching –1.1 by month’s end. 30
Its diameter shrinks from 20" Ensure you’re set up early with 25
to 15", so make the most of an unobstructed southwest hori- s 20 15 Nunki
early November for your best zon. As time ticks past nautical
views of the planet. You’ll also twilight, Howell is only 20° high. t Path of 10 5 Nov 1 q
see its phase change from 98 to Comet Howell
92 percent lit. The next time
the planet achieves an apparent The dark sky window opens for 2° M55 c
diameter over 20" will be 2033, one hour on November 4th, but M54
when it will be best seen from widens thereafter. At midmonth,
the Southern Hemisphere. it glides 3.5° beneath gas giants Comet Howell passes several objects this month. Jupiter, Saturn, and Pluto
Northern hemisphere observ- Jupiter and Saturn at almost 1° per are shown as they will appear on November 15, when Howell glides beneath
day. By the 18th, the Moon's light them. While you’re exploring the region, compare Howell’s appearance to
M75, described by discoverer Pierre Méchain as a “nebula without a star.”

becomes an issue once again.

Flex your observing muscles by comparing the comet’s appearance to the nearby globular star cluster

ers will have to wait until 2035. M75. At magnitude 8.6 and 6' across, M75 will masquerade as a near twin. Push the magnification past

This month, Neptune is 150x to see if one is more oblong than the other. Does each brighten at the center to a starlike core? Do

an easy target within 1° of their edges have similar softness?

38 ASTRONOMY • NOVEMBER

LOCATING ASTEROIDS I

The Bull noses a flower

A picture-perfect pairing ASTEROID 8 FLORA starts the month in the same field of view
as magnitude 3.5 Gamma (γ) Ceti, the middle of three modest
68 N points of light in a lonely eastern sky at midevening. The face of
E 30 Taurus, made of the V-shaped Hyades, points right at it. Ruddy
Aldebaran lights the trailhead.
p 25 NGC 7293 41
Night by night, Flora appears to shift westward by nearly half
20 47 the apparent width of the Moon each evening. Shining with
15 reflected sunlight, the magnitude 8.3 dot outshines many of
A Q UA R I U S the field stars of the celestial whale. From the 8th to the 10th,
Flora passes just above an upside-down triangle of 8th- to
Path of Ceres 10 9th-magnitude stars, perfect for catching its displacement with
a simple sketch — everyone can draw four dots, right?
5
Flora orbits between Mars and Jupiter in the main belt. It’s an
Nov 1 80-mile-wide, out-of-round planetesimal. It took four decades to
double the asteroid count up from 4 Vesta, with Flora’s discovery
PISCIS 2° by Englishman John Hind in 1847. By then, the evidence opposing
AUSTRINUS the theory that asteroids were the leftovers of an exploded planet
had begun piling up.
¡
Flora floats through the celestial whale
Dwarf planet Ceres is a binocular target that stays in Aquarius all month.
Astrophotographers will want to take note, as it spends several days near N
the Helix Nebula (NGC 7293).

and center the planet on the Mercury appears in a Path of Flora 30
first morning of the month to the morning sky of early Nov 1
spy Zaniah (Eta [η] Virginis) November, joining Venus as E 25
just 20' away. It’s almost as if two morning “stars.” It is mag- 5 10 15 20
Venus has a satellite. nitude 1.6 on November 1 and
brightens to match Spica at CETUS
Venus moves more than 1° magnitude 0.9 the next morn-
along the ecliptic each day. By ing. Mercury and Spica stand b 0.5°
November 5, it’s adjacent to side by side, separated by 4°, M77
Porrima (Gamma [γ] Virginis), rising an hour before the Sun.
with just 1° between them. A The rapidly brightening sky Asteroid Flora is not only relatively bright this month, but located
crescent Moon enters Virgo on offers a narrow window to against a backdrop of easy-to-spot stars as well.
November 11 and is 6.5° from catch the pair. To find the
Venus an hour before sunrise elusive planet, draw a line in brighten even though its See how far you can follow
on November 12. At the same your mind’s eye from Venus distance from Earth is increas- Mercury as it sinks lower each
time, Venus lies 18' from 4th- east toward the horizon, where ing because its phase is also morning. By November 20, it
magnitude Theta (θ) Virginis. you expect the Sun to rise. increasing. With a telescope, stands about 10° high in the
Look for two specks of light in you can follow it from 16 per- eastern sky 45 minutes before
Venus sits 4° due north of the twilight glow. Mercury and cent lit on November 1, through sunrise. That elevation drops to
Spica, Virgo’s brightest star, Spica stand a little less than 5° 50 percent on November 8, to 7° five days later, As November
on November 15. Both Venus high 45 minutes before sunrise. 85 percent lit by November 20. closes, the winged messenger
and Mercury are moving in The disk’s diameter shrinks flies into the brilliant glow of
tandem, now separated by 13°. Mercury increases in eleva- from 9" to 6" over the same the Sun, advancing into the
As Mercury is lost in twilight, tion and brilliance through period. evening sky in late December.
Venus maintains its brilliance, November 10, when it achieves
dimming by only 0.1 magni- greatest elongation (19°) from Don’t miss the stunning Martin Ratcliffe provides
tude. It quickly crosses the rest the Sun. Now an easy magni- view of a slender crescent Moon planetarium development for
of Virgo to reach neighboring tude –0.5, Mercury stands 13° standing 5° above Mercury Sky-Skan, Inc., from his home
Libra November 28. high at 6:15 A.M. local time for (now magnitude –0.7) in the in Wichita, Kansas. Alister
mid-northern latitudes in the predawn sky November 13. Ling, who lives in Edmonton,
Venus changes little this U.S. Venus is nearly 25° high. Spica shines 7° southwest of the Alberta, has watched the skies
month. On November 1, the Moon, while Venus is 8.5° west since 1975.
13"-wide disk is lit 82 percent. Following greatest elonga- of our satellite.
By November 30, it is 12" wide tion, Mercury continues to
and 89 percent lit.

GET DAILY UPDATES ON YOUR NIGHT SKY AT
www.Astronomy.com/skythisweek.

WWW.ASTRONOMY.COM 39

Gold from the

Humanity’s fascination
with this precious metal
is increased by knowing
it comes from the stars.

BY RAYMOND SHUBINSKI

Two neutron stars collide
somewhere in the depths
of space in this artist’s
concept. In addition to
generating gravitational
waves, such an event
can produce many heavy
elements, including gold.

UNIVERSITY OF WARWICK/MARK GARLICK

40 ASTRONOMY • NOVEMBER 2020

stars Gold is a child of Zeus;
neither moth nor rust
devour it; but the mind
of man is devoured by
this supreme possession.”

— Pindar, Greek poet,
5th century B.C.

a remote galaxy, two neutron
stars circled one another in a
ballet of ultimate destruction
and inevitable creation. Both
objects were the remnants of
massive stars, probably from a binary
system, that had become supernovae long
before. Each was incredibly massive, with
neutrons so closely packed that their
cores became diamond. The dance, alas,
could not go on forever and the stars
collided, releasing unimaginable energy
and sending gravitational waves speeding
through the fabric of space-time.
In 2017, 1.3 billion years later, astron-
omers detected those waves with the
Laser Interferometer Gravitational-wave
Observatory. Albert Einstein’s prediction
that the universe should be filled with
such faint ripples caused by gravity from
massive objects included sources such as
neutron star mergers. Yet finding a dis-
turbance in the fabric of space-time from
this kind of event had proven elusive
until then. When news of the detection
of gravitational waves broke, the media
wanted to know what else happens when
neutron stars collide. Astronomers
explained that, beyond the destruction
of the stars and the ripples in space, such
events also create all the heavy elements

we know in the blink of
an eye. But what did the
media key into? That
gold comes from
outer space.

This Minoan Gold-plated
gold bead was history
made between
2300 and 2100 It’s not surprising that
B.C. METROPOLITAN of the many elements
formed in the cataclysmic
MUSEUM OF ART destruction of massive
stars, gold should be the
one that captures our
imaginations the most.

WWW.ASTRONOMY.COM 41

scarcity made it desirable, and its
unchanging nature made it allur-
ing: Unlike silver, which turns
black, copper that goes green,
or iron that rusts, gold never
changes. It seems to be immortal
— a gift from the gods.

It took 20th-century science to
unravel this mystery. Iron, silver,
and copper rust or turn colors
due to reactions with oxygen.
Oxygen is always hungry for elec-
trons. Iron will give up two or
three electrons to oxygen and
will oxidize (rust) as a result.
Other elements also fall victim
to oxygen. But not gold. It’s the
most nonreactive of all metals
because it refuses to share elec-
trons with oxygen.

ABOVE: The mask of Elements necessary for life, such part of the grave goods Elemental facts
the Egyptian pharaoh as carbon, oxygen, potassium, belonging to a mysterious
Tutankhamun is one and sulfur, should rank higher on individual from Europe. Like all the heavy elements on
of the most famous a list of favorites. But we have an the periodic table, there just isn’t
ancient artifacts on emotional connection with gold. The ancient Egyptians had much gold to be found. If all the
Earth. Made mostly of vast gold mines far south of gold mined in human history
gold decorated with Thousands of years ago, their capital of Thebes, allowing were formed into one solid cube,
semiprecious stones, someone may have seen a shiny them to encase the mummy of it would measure about 70 feet
it weighs 22.6 pounds object in a stream and picked up Tutankhamun in the precious (21.3 meters) on a side. That
(10.23 kg). ROLAND UNGER/ a piece of gold. It must have metal. Few other ancient civiliza- would be around 183,000 tons
looked intriguing — though, tions had such wealth. When the of gold. Sounds like a lot, but if
WIKIMEDIA COMMONS because the metal is so soft, it’s mummy was unwrapped, archae- melted, it would fill only three
not very useful. Archaeologists ologists found two daggers. One and a half Olympic-size swim-
RIGHT: This gold coin have found a 6,500-year-old gold was made of what is now known ming pools. In 2018, Barrick Gold
from the First Persian bead in Bulgaria and recovered a to be meteoritic iron, and the Corporation’s mines in Nevada
Empire was struck nearly 3,000-year-old gold coin other was made of pure gold. processed millions of tons of ore
around 420 B.C. It from the Black Sea. The oldest to recover just 4 million ounces
honors King Darius II. known gold artifacts in England Gold was treasured, though (125 tons) of gold.
were found buried at Stonehenge, useful only as decoration or for
DEFLIM/WIKIMEDIA COMMONS trade, and not much else. But its Because it is so dense and
heavy, most of Earth’s gold
sank to the core of our planet.
Australian geologist Bernard
Wood estimates that 99 percent
of the world’s gold is buried thou-
sands of miles below our feet. He
also estimates that 1.6 quadrillion

42 ASTRONOMY • NOVEMBER 2020

The 1933 Saint-Gaudens double eagle is one of the rarest U.S. coins. Most of the more
than 445,000 minted were melted into gold bars. Only 13 specimens remain. NATIONAL

NUMISMATIC COLLECTION, NATIONAL MUSEUM OF AMERICAN HISTORY

tons of gold lie within the core. Sun: helium. Carbon, nitrogen, of meteors plunging into the The original Golden
Wood calculates that all this gold, iron, and all the heavier elements Sun. But scientists soon proved Spike, driven in by
if brought to the surface, would of the periodic table — including that the corona was made of Leland Stanford,
form a layer of the shimmering gold — were eventually identi- ultra-thin gas and demonstrated connected the Union
metal just 16 inches (40.6 centi- fied in a gaseous state in the that meteors would be an insuf- Pacific and Central
meters) thick. Compared to Sun’s atmosphere. ficient source of solar energy. Pacific railways in
Earth’s total size, that’s not much 1869 near Ogden,
gold. There is actually six times In the late 18th and early 19th Eventually, scientists calcu- Utah. It is on display
more platinum in our planet’s centuries, rock and mineral col- lated that the Sun contains almost at the Cantor Arts
core, which contains about 1 part lecting became the science of 2.5 trillion tons of gold, enough Center at Stanford
per million of gold. Gold is, in geology. Men and women such as to fill Earth’s oceans and more. University. WJENNING/
fact, quite rare. Charles Lyell, James Hutton, and Still, that’s just eight atoms of
the great fossil collector Mary gold for every trillion atoms of WIKIMEDIA COMMONS
Our golden Sun Anning, discoverer of the first hydrogen — a tiny amount when
Ichthyosaurus skeleton, clearly compared to the mass of the Sun.
Working one night in 1859, chem- demonstrated that Earth was far But how did gold come to be in
ists Robert Bunsen and Gustav older than the 6,000 years sug- the Sun and Earth?
Kirchhoff saw a fire raging in the gested by many contemporary
town of Mannheim, Germany, theologians. Lyell and Hutton Science is golden
about 10 miles (16 km) from their said Earth must be millions or
Heidelberg University labora- even billions of years old. If this For more than a millennium,
tory. They rolled their newly was true, what could keep the alchemists struggled to trans-
improved spectroscope (a device Sun and stars shining for such mute one element into another.
they invented that breaks light an incredibly long time? They were in search of the phi-
into its component wavelengths, losopher’s stone, which could
which allows chemical elements German physicist Julius turn base metals like lead and
to be identified) to the window Robert Mayer strongly favored mercury into gold. Even the great
and quickly detected the elements the meteoric theory of solar heat. Isaac Newton was fascinated
barium and strontium within He had calculated that, lacking
the bright glow given off by the an external source of energy, the
flames. Bunsen wrote that the Sun could shine for only 5,000
“same mode of analysis must be years. In 1848, he suggested the
applicable to the atmospheres of Sun was fueled by billions of
the Sun and the bright stars.” The meteorites raining down on it,
second half of the 19th century which provided its energy. This
saw an explosion of discoveries material also, supposedly, would
using this powerful tool. have brought heavy elements to
our star.
During the total solar eclipse
on August 18, 1868, several During the 1878 total solar
astronomers using spectroscopy eclipse, Cleveland Abbe,
detected a new element — and, it America’s first U.S. Weather
turned out, the universe’s second Bureau meteorologist, suggested
most abundant one — in the that the Sun’s corona, visible at
totality, was in fact this swarm

WWW.ASTRONOMY.COM 43

During the total solar by the idea of transmutation. of hydrogen into helium could magnets together gives a feel for
eclipse July 29, 1878, Indeed, some historians refer to be the powerhouse of the Sun. such repulsion. But collisions
Cleveland Abbe, him as “the last great alchemist.” Einstein’s famous equation showed happen, and protons fuse
America’s first U.S. But the tremendous forces of that incredible energy would be together. When four protons
Weather Bureau nature that create the elements released in such a process. eventually fuse, helium–4 forms,
meteorologist, were beyond the grasp of these releasing energy and making the
suggested that the early experimenters. Almost two decades after Sun shine.
solar corona was a Eddington and others began to
swarm of meteorites The origins of heavy elements explore fusion, German-American Our Sun contains enough
that provided the started to come into focus with physicist Hans Bethe described hydrogen to continue this fusion
energy for the Sun the publication of Einstein’s the now famous proton-proton process for another 5 billion
to shine. MICHAEL E. BAKICH general theory of relativity in chain reaction that explains how years. Eventually, helium will
1905. It was in this seminal work hydrogen fuses into helium. begin to fuse, forming the final
LIBRARY that the equation E=mc2 first Deep within the Sun is a vast products of carbon, nitrogen,
appeared. It wasn’t obvious at “soup” of hydrogen atoms con- and oxygen (element No. 8).
first just how important this sisting of one proton and one Within more massive stars,
equation was to our understand- electron each, which are in con- whose stronger gravity creates
ing of the universe, but its appli- stant, rapid motion. Most of the more pressure and heat, elements
cation to the problem of the Sun’s time, the electromagnetic force beyond oxygen can fuse. But this
immense energy output would repels any collisions. Trying process can continue only until
have far-reaching implications. to stick similar poles of two iron (element No. 26) forms at
Not only did it explain why the the center of giant stars, and
Sun and other stars could shine GOOD AS GOLD that’s when fusion shuts down.
for billions of years, but it also Finally, the star’s core will col-
helped show how elements The spectrum of gold shows the lapse and then rebound in a
heavier than hydrogen form. element’s unique fingerprints, which supernova explosion.
are used to identify its presence.
Most of us think of the first As the outer layers of the star
atomic bomb and splitting atoms MCZUSATZ/WIKIMEDIA COMMONS are blasted into space, one of two
— the process of nuclear fission neutron capture reactions takes
— when E=mc2 comes to mind. place. In both, free neutrons pen-
In 1920, however, Sir Arthur etrate the nuclei of nearby atoms
Eddington, then at Cavendish and are “captured” by elements
Laboratory in Cambridge, released in the explosion. Slow
England, thought that the fusing neutron capture (called “slow”
because radioactive decay into
other elements can occur before
other neutrons are captured)
creates about half of the elements
heavier than iron. But that still
leaves a lot of heavyweights on
the periodic table. To make the
rest, you need massive colliding
stars that produce rapid neutron
capture.

Once astronomers had pin-
pointed the source of the 2017

Atomic number 79
Atomic weight 196.96657

Density 19.3 grams/cm3
Melting point 1,947.52° F

(1,064.18° C)

44 ASTRONOMY • NOVEMBER 2020

SOLAR ENERGY Proton Gamma ray
Hydrogen-2 Helium-3
Proton

Neutron

Neutrino Hydrogen
Positron
Hydrogen Helium-3

Helium-4

The proton-proton cycle is the chain
reaction by which hydrogen fuses into
helium in the Sun’s core. The tiny bits of
mass that are converted to energy
satisfy Albert Einstein’s famous
equation, E=mc2. ASTRONOMY: ROEN KELLY

gravitational waves, researchers at computer. We coat sunglasses This illustration
the Max Planck Institute for and astronaut visors with it. Gold shows the
Astronomy were able to detect thread is used in electronics and spectroscope that
strontium in the maelstrom of in clothing. Nations pay their Joseph Norman
matter expanding into space at debts with gold. We make precious Lockyer used to
nearly 30 percent the speed of objects out of it, from jewelry to discover helium in
light. This element and others were religious artifacts. We put gold in the Sun’s atmosphere
formed by the rapid neutron cap- our teeth and even make toilets in 1868. WELLCOME IMAGES
ture reaction. The merger of these with it. Doctors inject patients
stars sent 1022 free neutrons flying with gold to help relieve rheu- WWW.ASTRONOMY.COM 45
through just 1 cubic centimeter of matoid arthritis. You can
space every second. even eat chocolate covered
in gold.
Such a high density of neutrons
creates conditions that allow exist- Carl Sagan
ing elements to quickly capture famously said
free neutrons. Strontium, thorium, we are made
uranium, and even gold form in a from the stuff
literal flash. And off they go into the of stars. So is the
depths of space. During the nearly world around us.
14-billion-year life span of our The next time you
universe, this has happened enough glance at the gold ring on
times to seed the nebulae that even- your finger or feel the gold
tually collapse to form solar systems chain around your neck, remem-
such as ours with gold — and all the ber that they are indeed a gift from
other heavy elements, too. the stars.

Gold standard Raymond Shubinski is a
contributing editor of Astronomy
Gold pervades our lives. The ele- who enjoys items made of gold.
ment is in every cellphone and

ObJsueprivtaert’isonmsooofns
These remote satellites have revealed scant
details to earthbound observers for more than
400 years, and offer a great observing challenge.

BY KLAUS BRASCH AND LEO AERTS

THE FOUR LARGE all four Galilean moons.
Moreover, under really steady
satellites of Jupiter, discovered seeing with a medium-size
in 1610 by Galileo Galilei, have scope, experienced observers
been viewed by more people can occasionally glimpse elu-
than any other planetary sive markings on Ganymede,
satellites besides the Moon. Jupiter’s largest moon.
They are favorites at star par-
ties and make an attractive Observational
sight alongside Jupiter. The history
famous moons also comprise
a distinctive association of Exactly what could be
bodies which individually observed on the jovian moons
would qualify as planets in was a topic of consider-
their own right. But, linked able dispute in the late 19th
with Jupiter, they are instead and early 20th centuries. In
considered a small analog 1900, astronomers Andrew
of the larger solar system. E. Douglass and William
H. Pickering published an
If the seeing (atmospheric extensive monograph in the
steadiness) is good, a 6-inch Annals of Lowell Observatory,
or larger telescope at high Volume II, detailing obser-
magnification will reveal the vations of Jupiter and its
tiny but distinct disks of

ABOVE: William H.
Pickering, along with
Andrew E. Douglass
and Percival Lowell,
founded Lowell
Observatory in
Flagstaff, Arizona. While
there, Pickering made
extensive observations
of planetary satellites.

LOWELL OBSERVATORY ARCHIVES

LEFT: Douglass made ABOVE: Douglass discovered a
this map of Ganymede relationship between the sunspot
showing the general cycle and tree rings, thus establishing
locations of features he the science of dendrochronology. He
observed through was also instrumental in founding the
Lowell Observatory’s Steward Observatory at the University
24-inch Clark refractor. of Arizona. LOWELL OBSERVATORY ARCHIVES

LOWELL OBSERVATORY ARCHIVES

46 ASTRONOMY • NOVEMBER 2020

Edward E. Barnard was an American astronomer best known for discovering Douglass made these drawings of Ganymede at Lowell Observatory in 1894
Barnard’s Star, unique for having the highest proper motion, and for creating and 1895, as he observed through 12-, 18-, and 24-inch refractors.
a catalog of dark nebulae within the Milky Way. INTERNET ARCHIVE BOOK IMAGES
LOWELL OBSERVATORY ARCHIVES

These sketches of
Ganymede and Callisto
were made in 1983 by
Astronomy columnist
Stephen James
O’Meara, using the
9-inch refractor at
Harvard College
Observatory.

STEPHEN JAMES O’MEARA

moons that they made in 1894 in 1897, including a map of dismissed by Lowell for San Jose, California, renowned
and 1895. the features he recorded. doubting their reality. After astronomer Edward E.
moving to the University of Barnard used the then-largest
Working in Mexico and Pickering was a rather Arizona in 1906, Douglass telescope in the world, the
at Lowell Observatory in eccentric individual; among became head of Steward 36-inch Clark refractor, to
Flagstaff, Arizona, with two other extraordinary theories, Observatory and founded the undertake similar observa-
refractors — an 18-inch he believed that Jupiter’s new science of dendrochro- tions of Ganymede and
Brashear and a 12-inch Clark moons were not solid bodies nology, which dates historic Callisto from 1893 through
— mounted in tandem, the but low-density aggregates of events using the annual 1895. His results were also
astronomers undertook an dust and meteoric debris. growth rings of trees. published in Astronomische
ambitious visual program. That undoubtedly colored Nachrichten in 1897, in a paper
Their goal was to estimate the his impressions that they At Lick Observatory, near
ellipticity, rotational periods, appeared elliptical through Dale P. Cruikshank
and surface features of what the telescope, as well as reported seeing detail
they called satellite I (Io), II accounts for his obsession on Ganymede on
(Europa), III (Ganymede), and with measuring their “elliptic- November 3, 1963, while
IV (Callisto). The common ity.” Other observers subse- observing through a
names, originally assigned by quently showed that the 16-inch reflector at 800x
Galileo’s contemporary Simon presumptive ellipticity of the at Kitt Peak National
Marius, did not become offi- moons reported by Pickering Observatory. D.P. CRUIKSHANK
cial until the 20th century. was illusory, likely due to con-
trast or astigmatic effects.
Douglass subsequently
undertook a more detailed Douglass, a talented
study of Ganymede with the astronomer and botanist, was
newly commissioned 24-inch at that time strongly influ-
Clark refractor at Flagstaff. enced by his boss, Percival
He published the results in Lowell, regarding his views of
the prestigious journal Mars and its putative network
Astronomische Nachrichten of canals. He was later

WWW.ASTRONOMY.COM 47

19h02 UT

Co-author Aerts took the image of Ganymede on the left through a DMK webcam
attached to a 14-inch Celestron with a 2.5x PowerMate, with the addition of a red
filter. The comparative image of Ganymede on the right was generated using the
Solar System Simulator provided by Jet Propulsion Laboratory (JPL). LEO AERTS

described: “On February 20th estimated at less than 0.1"

… an interval of extremely or 200 miles. In appearance,

good seeing revealed the from the drawings, these

19h05 UT Great Northern Belt in markings very much resemble

longitude 260° to 20°, with those seen at the same obser-

perfect distinctiveness and vatory upon Mars, Venus and

definition.” Mercury.”

In sharp contrast to These strident comments,

Douglass and Pickering, well documented in William

Barnard’s drawings of Sheehan’s memorable biogra-

Ganymede and Callisto show phy of Barnard, The Immortal

far more diffuse features: Fire Within, point to the

19h07 UT “Though conspicuous enough, rivalry and disagreements

Compare the images of Ganymede above, taken May 5, 2016, to the one generated they were so vague in form between the two observatories.
by JPL’s Solar System Simulator (this page, top right). All were taken through a that at no two times was it They were most glaring with
14-inch Celestron with a 1.8x Barlow lens, and an ASI 120MM-S webcam. LEO AERTS possible to say definitely that respect to the putative martian

the same marking was under canals and similar features as

observation.” He goes on to depicted by Percival Lowell

titled “On the Third and 15 minutes. The north polar say, “I have been very much and others. Much of the diver-

Fourth Satellites of Jupiter.” cap seen by some observers is interested in Mr. Douglass’ gence hinged on Lowell’s

Differences arise immediately north of this con- paper on the third and fourth claims that while his tele-

spicuous northern belt and is satellites of Jupiter.” After scopes were of smaller

The Lowell observations show probably caused by contrast.” Barnard mentioned that he aperture, seeing conditions at

predominantly banded and Other astronomers later used the much larger 36-inch the high and dry elevation of

crossed streaks on all four showed that Jupiter’s main Lick refractor to make his Mars Hill were unequaled.

satellites, and also provide moons are tidally locked and observations, he wryly added, To that, Barnard countered

detailed descriptions of each. rotate synchronously with “According to Mr. Douglass’ that it was his belief that no

Ganymede is summarized their planet like our Moon. drawings and statements, he existing telescope, except the

as: “The third satellite was In his subsequent 1897 paper, finds these satellites covered 40-inch Yerkes refractor, “is

observed with much greater Douglass appears more cer- by a series of fine dark lines, so capable of showing the sur-

ease and gave more satisfac- tain of the key markings he the maximum width being face features of these satellites

tory results. The detail is

conspicuous, and consists of

northern and southern belts

parallel to the equator, and

other markings. The northern

belt becomes visible 2.2 [days]

after superior conjunction. Its

position is easily determined,

and between 1894 and 1895

gives a means for measur-

ing very exactly the rotation

period. It shows that the rota-

tion of detail agrees with revo- In 2015, co-author Aerts captured the webcam image at left of Ganymede transiting Jupiter with a 14-inch Celestron
lution about Jupiter within
Schmidt-Cassegrain telescope. He also made a simultaneous sketch of the satellite, at right. LEO AERTS

48 ASTRONOMY • NOVEMBER 2020

A Hubble Space Telescope image of Ganymede emerging
behind Jupiter is shown at left. Co-author Aerts took the
comparable image at right through a 14-inch Celestron
Schmidt-Cassegrain telescope. LEO AERTS

as the Lick 36-inch. I also visible details on all four and Callisto with this same as instrumental and atmo-
believe there are brief inter- Galilean moons. They were telescope. Regarding the latter, spheric variances, it seems
vals of good seeing at the observing with a 24-inch he advises, “Seeing detail on clear that visual reports of fea-
Lick Observatory which are refractor at Pic du Midi the jovian moons requires tures on Jupiter’s largest moon,
not excelled if indeed they Observatory in France, exceptional seeing, and the Ganymede, must be taken
are equaled at any other known for its legendary steady best views are [obtained] with considerable skepticism.
observatory.” seeing and clear skies. through astronomical twi- While there is general agree-
light. Spend a minimum of ment that the satellite exhibits
Well over a century later, Current observations 30 minutes looking, waiting diffuse dark and light regions,
what can we conclude as to for moments of perfect seeing, and there are references by
who was right and what in One can argue that jovian and confirm and reconfirm several of the early observers
fact can be observed of the moon detail should be well any initially suspected struc- to “bright polar caps,” the
jovian moons’ features using within visual reach of large, ture at least three times.” notes of Barnard, O’Meara,
earthbound telescopes? Both professional telescopes, but and Cruikshank all urge cau-
authors of this piece have what about smaller, more Likewise, during his stu- tion in their accompanying
spotted vague detail on typical amateur instru- dent days, Cruikshank notes: “extremely difficult”;
Ganymede through a 14-inch ments? Clearly, it depends reported detail on Ganymede “probably unreliable”; “seemed
Schmidt-Cassegrain telescope on a number of factors: the with his 12-inch reflector, a real, but …”; and so on.
on rare occasions of out- quality of the optics, the see- 16-inch reflector at KPNO,
standing seeing. And one ing, the magnification, and and the 40-inch refractor at On the other hand, today,
of us, Brasch, even saw ruddy perhaps most importantly, Yerkes Observatory. More thanks to the tremendous
patches on Io while observing the observer’s experience and recently, co-author Aerts advances in digital imaging
with Lowell Observatory’s visual acuity. sketched and simultaneously and processing, amateur
4.3-meter Discovery Channel imaged details on Ganymede astronomers with just
Telescope. Well-known Before the Voyager space- with a 14-inch Schmidt- medium-size telescopes can
planetary scientist Dale P. craft flybys of Saturn in 1980 Cassegrain telescope. capture outstanding images
Cruikshank likewise observed and 1981, Astronomy maga- of Jupiter and its moons,
details as a student with the zine’s eagle-eyed Stephen These results once again unheard of just a decade ago.
82-inch Otto Struve telescope James O’Meara (then a raise questions as to the reli- It is indeed a golden age of
at McDonald Observatory, student) spotted the spokes ability of visual reports. In an amateur astronomy.
as well as with smaller instru- in the planet’s B ring. He effort to answer them, we
ments at Kitt Peak National also accurately determined undertook a side-by-side com- Klaus Brasch is a retired
Observatory (KPNO) and the rotation period of Uranus parison of visual observations bioscientist and volunteer at
elsewhere. with the 9-inch Clark refrac- from several sources, with Lowell Observatory in Flagstaff,
tor at Harvard College modern digital images of the Arizona. Leo Aerts is a Belgian
In addition, in the 1940s, Observatory. In 1983, Galilean moons. Making amateur astronomer specializing
French astronomer Bernard O’Meara went on to spot mot- allowances for stylistic differ- in solar system imaging.
Lyot and others reported tled markings on Ganymede ences among observers, as well

WWW.ASTRONOMY.COM 49

While the universe is vast, this
selection of stamps can shrink
it down to a manageable size.

BY KATRIN RAYNOR-EVANS

IMAGINE CARRYING You may have guessed that The author exhibits a
I’m talking about postage collection of stamps
the universe in your pocket stamps. I’ve had a lifelong inter- and first day covers
before sending it halfway across est in astronomy, but I didn’t at a celebration of
the world. Of course, you can’t turn my attention to stamp the 50th anniversary
actually carry the entirety of collecting until a few years ago. of the Moon landing,
the universe, but you can carry This new hobby ignited when, at National Museum
a small, weightless surrogate while leafing through my Wales in Cardiff.
that’s just as beautiful. These father’s stamp collection,
could include a colorful array I spotted a science-fiction-
of astronauts, rockets, galaxies, themed stamp. I soon won-
and nebulae, on canvases about dered what other topics
1 inch in size.

50 ASTRONOMY • NOVEMBER 2020