your guide to planets stars and galaxies

8112019 Your Guide to Planets Stars and Galaxies

httpslidepdfcomreaderfullyour-guide-to-planets-stars-and-galaxies 114

5 0 0

F A C T S I N S I D

EYour guide to

planets starsand galaxiesby Richard Talcott

A supplement to Astronomy magazine

8129copy 2012 Kalmbach Publishing Co This material may not be reproduced in any formwithout permission from the publisher wwwAstronomycom



Saturn

Mars

Marsrsquo ruddy appearance arisesbecause the sand on the planetrsquossurface consists largely of ironoxides mdash rust NASAJPLMSSS

Saturnrsquos rings consist of icy particlesranging in size from tiny motes tohouse-sized icebergs NASATHE HUBBLE

HERITAGE TEAM 983080STSCIAURA983081

F U N

Mars boasts the largest vol-canoes in the solar system

although theyrsquore all extinctThe biggest mdash OlympusMons mdash spans nearly 400miles and rises 13 milesabove the surrounding plain

F A C T

Earth may seem extraordinary to those who call it homebut itrsquos not a land of superlatives Earth is neither too hot

nor too cold too big nor too small Itrsquos just right in so

many ways mdash the perfect ldquoGoldilocksrdquo planet Of course

as the only known abode of life in the universe Earth

does have one major claim to being special The other planets in

the solar system leave their marks in different ways

The planets divide into two broad categories terrestrial and

jovian The small rocky terrestrial planets include Mercury

Venus Earth and Mars Mercury the closest to the Sun bakes

at temperatures up to 800deg Fahrenheit at noon But Mercuryrsquos

razor-thin atmosphere canrsquot hold heat at night the temperature

plummets far below freezing Venus most resembles Earth inmass and diameter but a thick atmosphere of carbon dioxide

has led to a runaway greenhouse effect Venusrsquo surface remains

a scorching 865deg F year-round

Earth and Mars are the water worlds of the solar system

Our home planet is the only one with liquid water at the surface

now but spacecraft observations during the past 15 years leave

no doubt that Mars once had loads of surface water Even now

Mars has permafrost and permanent polar caps of water ice

Winds up to 70 mph blow around the ubiquitous martian dust

creating shifting seasonal patterns

The jovian planets mdash Jupiter Saturn Uranus and Neptune

mdash are all gaseous behemoths They consist mostly of hydrogen

and helium the most abundant elements in the universe Jupiter

dwarfs the others It contains more than twice as much matter

as all the other planets combined All the jovian planets pos-

sess ring systems but only Saturnrsquos appears bright Its icy rings

span 170000 miles and measure just 100 feet thick Uranus

and Neptune are the true twin planets of the solar system with

nearly equal diameters masses compositions and rotations

Most scientists no longer consider small distant Pluto to be a

major planet A mixture of ice and rock this world more closely

resembles the thousands of so-called Kuiper Belt objects that

lurk beyond Neptune In 2006 astronomers demoted Pluto to a

ldquodwarf planetrdquo a category that also includes the asteroid Ceres

Planetsof thesolar system

2 Your guide to planets stars and galaxies



Planet Distance from Sun Orbital period Diameter Mass De (Earth=1) (Earth=1) (Earth=1) (wa

Mercury 039 8797 days 0383 0055 5

Venus 072 22470 days 0949 0815 5

Earth 100 36526 days 1000 1000 5

Mars 152 68698 days 0532 0107 3

Ceres 277 460 years 0075 00002 1

Jupiter 520 1186 years 11209 317832 1

Saturn 958 2946 years 9449 95159 0

Uranus 1920 8401 years 4007 14536 1

Neptune 3005 16479 years 3883 17147 1

Pluto 3948 24768 years 0187 0002 1Note Ceres and Pluto are officially considered to be dwarf planets

Solar system planets

rcurys high density meansre than half of it must be madehe heavy elements iron and

kel NASAJPLUSGS

Venus

Pluto amp Charon

Jupiter

ercury Earth

ranus Neptune

Nearly three-quarters ofEarthrsquos surface is covered withwater Itrsquos what makes our homeworld conducive to life NASA

The orbit of dwarf planet Pluto (left along with its moon Charon) brings it cto the Sun than Neptune for 20 years out of its nearly 250-year-long circuit ESA

Thick clouds blanket Venus so astronomers use radar toits surface The atmospheric pressure there is nearly 100 tithat at Earthrsquos surface NASAJPL

Jupiter is so big that it would take 11 Earths wedged side by side to cross thegiantrsquos girth and more than 1000 Earths to fill its volume NASAJPLUNIVERSITY OF AR

nusrsquo bland cloud tops maskfact that its rotation axis lies in

orbital plane so night and day atpoles last 40 years each NASAJPL

Storms rage in Neptunersquos atmos-phere as they do in the massiveatmospheres of most of the jovianplanets NASAJPL

F U N

Saturn has the lowest densityof any planet In fact if youfilled a solar-system-sized

basin with water the ringedworld would float

F A C T

F U N

Sunlight takes just eight min-utes to reach Earth but more

than four hours to cross thevoid to Neptune and Pluto

F A C T




After the Sun and planets therersquos not much else in the

solar system mdash certainly not in terms of mass But

in sheer number (and in a few notable instances

prominence) the small objects hold their own The

biggest of the small bodies actually outrank the small-

est planet Both Ganymede a Jupiter moon and Titan a Saturn

moon have diameters larger than Mercury More than 170

moons have been discovered orbiting the eight planets although

the vast majority are little more than flying boulders

The smaller planets tend to have fewer moons Earth has just

one which formed when an object the size of Mars struck the

proto-Earth ejecting debris that eventually coalesced Mercuryand Venus have no moons and Mars possesses just two small

ones Oddly enough Plutorsquos large moon Charon is half the diam-

eter of the dwarf planet mdash the largest ratio in the solar system

The hefty moons of the gas giants garner most of the atten-

tion Jupiterrsquos four big moons mdash Io Europa Ganymede and

Callisto mdash form a miniature solar system Io ranks as the most

volcanically active object in the solar system Europa hides an

ocean of liquid water mdash perhaps larger than all of Earthrsquos oceans

mdash beneath its frigid ice crust Giant Ganymede also may harbor

an ocean and has a surface covered with intriguing grooved ter-

rain And Callisto sports more craters than any other object in

the solar system At the top of Saturnrsquos family of moons is Titan

which possesses a significant atmosphere and methane lakes

More than half a million asteroids also inhabit the solar system

The biggest Ceres has a diameter of 600 miles Yet most are far

smaller If you add them all up asteroids donrsquot equal the weight

of Earthrsquos Moon Most asteroids circle the Sun between the orbits

of Mars and Jupiter although a few wander into Earthrsquos vicinity

Perhaps the most spectacular small bodies are comets

Billions of these ldquodirty snowballsrdquo lurk in the outer solar sys-

tem If their long looping orbits bring them close to the Sunrsquos

warmth they shed gas and dust The Sun then blows this mate-

rial back to create a long tail Although a cometrsquos nucleus may be

only a mile or two across its tail can stretch millions of miles

Small bodiesof the solarsystem

Titan

Europa

Io

Titanrsquos hazy atmosphere glows as it scatters incom-ing sunlight The atmosphere of Saturnrsquos moon isthicker than Earthrsquos and like ours contains mainlynitrogen NASAJPLSSI

Ridges crack the surface of Jupiterrsquos moonEuropa Such ridges could be sites whereslushy water erupted through the icy surfaceand then froze NASAJPL

More than 100 active volcanoes dot the surfaceof Jupiterrsquos moon Io The plumes can reach 100miles high and spread debris over thou-sands of miles NASAJPL




Moon Planet Distance from Orbital period Diameter Den

planet (miles) (days) (miles) (wat

Moon Earth 238900 2732 2160 3

Io Jupiter 262100 177 2263 3Europa Jupiter 417000 355 1940 3

Ganymede Jupiter 665100 715 3271 1

Callisto Jupiter 1169900 1669 2994 1

Enceladus Saturn 147900 137 313 1

Tethys Saturn 183100 189 660 1

Dione Saturn 234500 274 698 1

Rhea Saturn 327500 452 949 1

Titan Saturn 759200 1595 3200 1

Iapetus Saturn 2212600 7933 913 1

Ariel Uranus 118600 252 719 1

Umbriel Uranus 165300 414 727 1

Titania Uranus 271100 871 980 1

Oberon Uranus 362600 1346 946 1

Triton Neptune 220400 588 1681 2Charon Pluto 12200 639 753 1

Major moons

ErosHale-Bopp

Callisto

One of the brightest comets of the past40 years Hale-Bopp wowed observersin 1997 It had a nucleus 25 miles wideand a tail that stretched more than 100million miles BILL AND SALLY FLETCHER

Saturnrsquos icy moon Enceladus reflectsmore than 90 percent of the sunlightthat reaches it the highest percentageof any object in the solar system NASAJPL

PhobosLike most small moons in the solarsystem Marsrsquo Phobos measures just a

few miles across and has an irregularshape NASAJPLMSSS

F U N

Iorsquos active volcanoes andEuroparsquos underground oceanof liquid water both stemfrom enormous tidal forcesmdash which flex and heat themoonsrsquo interiors mdash exerted

by Jupiterrsquos massive gravityF A C T

Multi-ringed impact basins some stretching more than1000 miles formed on Jupiterrsquos Callisto when massiveimpacts left concentric fractures and faults NASAJPL

Potato-shaped asteroid Eros some 20 miles long looks likea lot of other modest-sized asteroids but this object mightone day wander dangerously close to Earth NASAJHUAPL

Triton

nceladus

eyser-like plumes eposited the darktreaks seen on Nep-unersquos moon Triton At aemperature of ndash390deg F Tritonas the coldest surface known in

he solar system NASAJPL

F U N

Saturnrsquos enigmatic outermoon Iapetus has a splitpersonality Half of its surface

appears as dark as freshly laidasphalt while the oppositehemisphere reflects as muchlight as newly fallen snow

F A C T



Protostar

A

ll stars begin their lives in the vast clouds of gas and

dust that litter galaxies like the Milky Way A single

cloud can produce hundreds or even thousands of

stars Something triggers the cloud to start collaps-

ing mdash perhaps strong winds from a massive star ora nearby supernova explosion mdash and gravity works its magic

The cloud fragments and each pocket of material continues to

contract and heat up

The contracting star becomes stable when it starts to gener-

ate energy by nuclear fusion Four hydrogen atoms combine to

form one helium atom Because one helium weighs slightly less

than the four hydrogens combined the reaction creates energy

according to Einsteinrsquos equation E=mc2

The biggest stars contain up to about 120 times as much

material as the Sun They burn hot and use their fuel rapidly

These luminaries may have a surface temperature of 70000deg F

radiate nearly a million times the Sunrsquos light and survive onlya few million years

The Sun shines at about 10000deg F and will last some 10

billion years (itrsquos about halfway through now) The smallest

stars have 8 percent of the Sunrsquos mass and glow at only 3000deg

to 4000deg F mdash so dim that they can shine for a trillion years

Once a star exhausts its hydrogen fuel the end is nigh First

it swells into a red giant expanding to a diameter of hundreds of

millions of miles and cooling to a few thousand degrees It may

tap into more nuclear reactions converting helium to carbon

for example but eventually those

fuels run out as well Stars with up

to about eight times the Sunrsquos mass

eventually puff off their outer layers

and form glowing gas clouds known

as planetary nebulae The star itself

settles down as a white dwarf

More massive stars typically die

in supernova explosions Such explo-

sions scatter the heavy elements built

up during the starrsquos life forming

the raw material for new stars and

perhaps planets The collapsed remnant of the exploded star

becomes either a rapidly spinning neutron star or a black hole

whose gravity is so strong that not even light can escape

Stars inour galaxy

The Sun

Most people think of the Sun as the anchor of our solar system mdash andthatrsquos certainly true It contains 998 percent of all the matter in the solasystem But to astronomers the Sun has even more importance It is theonly star in the universe that appears as more than a point of lightthrough a telescope Detailed observations of the Sun led scientists tounderstand how stars shine how they radiate energy and even howhuge storms wrack their surfaces NASASOHO

The life of a Sun-like star

N49

Heavy elements forged in a massive star spreadout at thousands of milesper second in supernovaremnant N49 One daythese elements may beincluded in a new stellargeneration NASATHE HUBBLE

HERITAGE TEAM 983080STSCIAURA983081F U N

Astronomers divide stars intoseven main spectral classesGenerations of students havelearned the sequence byusing the first letters in thesentence ldquoOh Be A Fine Girl(or Guy) Kiss Merdquo

F A C T




Main sequencesolar-type star

Red giant Asymptotic-giant-branch star Protoplanetary nebula Planetary nebula White dw

Spectral Mass Temperature Main sequence Examples class (Sun=1) (Fahrenheit) radius (Sun=1)

O 20ndash120 greater than 55000deg 12ndash25 Zeta (ζ) Puppis

B 4ndash20 17100degndash55000deg 4ndash12 Rigel Spica

A 2ndash4 12300degndash17100deg 15ndash4 Sirius Vega

F 105ndash2 10300degndash12300deg 11ndash15 Canopus Procyon

G 08ndash105 9000degndash10300deg 085ndash11 Sun Capella

K 05ndash08 6700degndash9000deg 06ndash085 Aldebaran Arcturu

M 008ndash05 3100degndash6700deg 01ndash06 Antares Betelgeus

Star characteristics

Stars like the Sun condense out of a gaseous cloud The growing protostar develops a disk (which may form planets)and shoots out material before settling down as a main sequence star converting hydrogen to helium Once the hydro-gen runs out the star swells to a red giant and becomes unstable as an asymptotic-giant-branch star before puffing offits outer layers as a planetary nebula The starrsquos core remains as a dense white dwarf ASTRONOMY ROEN KELLY

Surface of the SunCatrsquos Eye Nebula

Cone Nebula

New stars form from clouds of gas and dust such asthe Cone Nebula Hot stars ionize the surroundinghydrogen gas which glows with a characteristic redcolor NASAESATHE ACS SCIENCE TEAM

When the Sun dies in 5 billion years it may resem-ble the symmetric Catrsquos Eye Nebula Here glowingstrands of ionized gas mark where a dying starrepeatedly shed its outer layers NASAESAHEIC

THE HUBBLE HERI TAGE TEAM 983080STSCIAURA983081

An intricate honeycomb on the Sunrsquos surface marks regionswhere heat (bright areas) rises and cooler material (dark areasinks in a process called convection ROYAL SWEDISH ACADEMY OF SCIE

F U N

To shine as brightly as it doesand nourish life on Earth theSun must convert 600 milliontons of hydrogen into heliumevery second

F A C T



S c u t

u m - C

e n t a

u r u s

A r m

Norma Ar m

C e n t r a l b a r

S a g i t t a r i u s A

r m

P e r s e

u s A

r m

O r i o n

S p u r

Sun

The MilkyWay Galaxy

Head outside on a clear dark summerrsquos night and your

eyes will be greeted by thousands of stars All of them

belong to our galaxy as does virtually everything

else you can see with the naked eye If you let youreyes adjust to the darkness yoursquoll see a gauzy whitish

band running across the sky This is the Milky Way mdash the com-

bined light of countless stars mdash and the feature that lends its

name to our galaxy

The Milky Way is a giant barred spiral galaxy that stretches

about 120000 light-years from end to end but whose disk mea-

sures only some 1000 light-years thick The central bar extends

28000 light-years The Sun lies about halfway between the gal-

axyrsquos center and edge and revolves at approximately 150 miles

per second taking roughly 225 mil-

lion years to complete one circuit of

the galactic hubThe most obvious sights of the

galaxy are stars Astronomers esti-

mate between 200 and 400 billion

populate the Milky Way Galaxy

(most are hidden from view or

extremely faint so a precise count

isnrsquot possible)

Because the hottest brightest stars

are also short-lived mdash and the spiral

arms are the only place in the galaxy

with active star formation mdash the arms stand out The clouds

of gas and dust from which stars form also call the spiral arms

home as do the open star clusters that emerge from them

The nuclear bulge of the galaxy consists mostly of old stars

It measures about 12000 light-years across At the galaxyrsquos heart

lies a supermassive black hole that weighs approximately 4 mil-

lion Suns Surrounding the bulge and disk is a vast spherical

halo that stretches some 300000 light-years

The most prominent members of the halo are globular

clusters These ancient collections of up to a million stars each

were born at the same time as the galaxy some 12 billion to 13

billion years ago They contain few heavy elements because they

formed before supernova explosions had enriched the inter-

stellar medium with them

Structure of the Milky Way

The Pleiades M3

Star formation in Cygnus

F U N

Most naked-eye stars aremassive and highly luminousones that shine across greatdistances But this gives a dis-torted view of the galaxy as awhole In actuality cool dimM-type stars make up abouttwo-thirds of all stars in theMilky Way

F A C T

A stellar nursery in Cygnus harbors many massive young stars Invisibloptical light the DR21 complex shows up when viewed in dust-penetratinfrared radiation NASAJPL983085CALTECHA MARSTON 983080ESTECESA983081

Open star clusters like the Pleiadescontain dozens to hundreds of starsThese groups lie in our galaxyrsquos spi-ral arms and disperse over billionsof years JASON WARE

Globular star clusters have eas long as the Milky Way M3 p500000 stars in a sphere 160 years across S KAFKA AND K HONEYC

INDIANA UNIVERSITYWIYNNOAONSF

The Sun lies in the Orion Spur one of several arms and smaller appenda

where our galaxy creates stars Astronomers name the spiral arms after tconstellation where they appear prominent NASAJPL983085CALTECHR HURT 983080SSC983085CALT8 Your guide to planets stars and galaxies



F U N

Much of the Milky Way Galaxyand its structure remain hid-den to earthbound observersbecause dust chokes the spi-ral arms Itrsquos like being in thewoods and trying to discernthe forestrsquos form

F A C T

F U N

In measuring distances inthe galaxy and the universeastronomers use a unitknown as the l ight-year Itrepresents the distance abeam of light travels in oneyear At 186000 miles persecond light traverses 59trillion miles in a year

F A C T

band of dust cuts through the Milky Way blocking light

om distant stars If not for all the dust the galaxyrsquos centerould shine brighter than the brightest star STEVE THORNTON

F U N

A century ago astronomersthought the Sun occupiedthe center of the galaxy Butcareful studies of globularclusters which orbit theMilky Wayrsquos center and tendto gather in the constellationSagittarius show we livehalfway to the edge

F A C T

F U N

How do astronomers knowa black hole resides at theMilky Wayrsquos center They havefound stars near the centralhub orbiting so fast that theymust be circling an invisibleobject containing 4 millionsolar masses

F A C T



T

he collections of stars gas and dust known as galaxies

form the building blocks of the observable universe

Roughly 125 billion galaxies populate the cosmos and

they come in all shapes and sizes Astronomers divide

galaxies into three major categories spirals ellipticalsand irregulars A spiral has a broad disk containing clouds of gas

and dust and from two to several spiral arms a nuclear bulge of

old stars and a spherical halo that envelops both

Approximately one-third of spirals exhibit central bars mdash a

symmetric concentration of stars and sometimes gas and dust

that crosses the nucleus and connects with the outer spiral arms

(Recent studies show the Milky Way possesses a significant bar)

The diameters of spirals range from roughly 20000 to more

than 100000 light-years and they contain anywhere from sev-

eral billion to several hundred billion stars

Elliptical galaxies appear spherical or flattened in shape

They possess little of the gas and dust seen in the disks of spiralgalaxies so they donrsquot generate any new stars Ellipticals show

the widest range in size of any galaxy type Giant ellipticals can

span 1 million light-years and contain several trillion stars

dwarf ellipticals may be only a few thousand light-years across

and have millions of stars An important intermediate type of

galaxy has a disk like a spiral galaxy but contains no gas or dust

Astronomers call this type of galaxy a lenticular

Irregular galaxies donrsquot show any symmetry or organized

spiral structure The category exists basically as a catchall for

galaxies that donrsquot fit either the spiral or elliptical classification

Irregulars can be big containing up to 100 billion stars or as

small as dwarf ellipticals Astronomers think most irregulars

result from the collisions or mergers of two or more galaxies

The gravitational interactions disrupt normal spiral or elliptical

structure leaving behind a chaotic appearance

Most galaxies belong to groups with dozens of members or

to clusters with up to thousands of members The Milky Way

joins with the slightly larger Andromeda Galaxy to form the

cornerstones of the Local Group a collection of roughly 50 gal-

axies that spans several million light-years The vast majority of

Local Group galaxies are dwarf ellipticals and irregulars Small

groups generally have a few dozen member galaxies but clusters

can contain several thousand galaxies The Virgo cluster located

50 million light-years away is the nearest large cluster to Earth

Galaxies

in theuniverse

The Mice

NGC 4414

Multiple spiral arms wind out from the nucleus ofNGC 4414 Young blue stars throng the armswhile older redder stars populate the nuclearbulge NASATHE HUBBLE HERITAGE TEAM 983080STSCIAURA983081

The ldquoMicerdquo are two spiral galaxies in the process of merging Gravity haspulled material out of each to form long tails while compressed gas cloufuel new star formation NASAESATHE ACS SCIENCE TEAM

M87

A high-speed jet shoots from the heart of the giant

elliptical galaxy M87 (upper left) in the Virgo cluster A black hole of some3 billion solar masses drives this activity NASATHE HUBBLE HERITAGE TEAM 983080STSCIAUR

Giant elliptical galaxies M84 (left) and M86 (right)each contain a trillion stars These two dominate the central regionof the nearby Virgo cluster a collection of some 2000 galaxies NOAOAURA

M84 amp M86




NGC 68221760 kly

Ursa Minor Dwarf 225 kly

Draco Dwarf

248 kly MilkyWay

SMC189 kly

NGC 1852020 kly

NGC 1472460 kly

Andromeda Galax

2510 kly

Pinwheel Galaxy (M33)

2770 kly

Leo I818 kly

Leo II750 kly

Sextans

Dwarf 293 kly

LMC160 kly

The Local GroupThe Milky Way and Andromeda galaxiesrule the Local Group accounting for morethan half its mass Distances from our galaxy

are given in thousands of light-years (kly) ASTRONOMY ROEN KELLY

F U N

If you examine the brightestgalaxies some 75 percent arespirals 20 percent ellipticalsand 5 percent irregularsIncluding faint dwarfs skews

the numbers to 30 percentspirals 60 percent ellipticalsand 10 percent irregulars

F A C T

ndromeda Galaxyghtly bigger than the Milky Way the Andromeda Galaxy (M31) containsme 500 billion stars Located 25 million light-years away the galaxy can bempsed with the naked eye MICHAEL STECKER

he LMC

e Large Magellanicoud (LMC) is an irregular

axy about 160000ht-years from Earth Thedish cloud at top righthe Tarantula Nebula

e largest known regionstar formation LUKE DODD

F U N

The Large and SmallMagellanic Clouds (LMCand SMC) are satellite galax-ies to the Milky Way They liedeep in the southern sky andwere not seen by Europeansuntil Magellanrsquos around-the-world voyage

F A C T

F U N

The Andromeda Galaxy mayseem a good neighbor tothe Milky Way but it wonrsquotalways be so Astronomersthink that in approximately 5billion years our two galaxieswill collide and merge

F A C T



H

ow did the universe get to be the way it is today It

might seem a hopeless question at first at least until

scientists invent a time machine to take us back But

astronomers have invented such an instrument mdash they

call it a telescope Herersquos how it works Because lighttravels at a finite speed (186000 miles per second) the light we

receive on Earth left its place of origin some time ago The far-

ther we look into space the further we peer back in time

When astronomers first studied galaxies in the early 20th

century they found the farther a galaxy was from Earth the

faster it appeared to be moving away If you think of this expan-

sion as a movie and run it backward then all of the galaxies

must have been much closer together in the past This led to

the idea of the Big Bang mdash the theory that all matter in the uni-

verse started out together and then something triggered a rapid

expansion that continues today

But is there any proof of such an extraordinary beginningYes mdash lots of it Astronomers looking ever deeper into space

find that the universe was surprisingly different Instead of the

stately spiral and elliptical galaxies we see now there were lots

of galactic fragments that were colliding merging and creat-

ing general havoc The activity dumped fuel onto supermassive

black holes at the centers of nascent galaxies creating highly

luminous quasars All this action took place mdash in fact could

only take place mdash in a universe much smaller than todayrsquos

Radio astronomers have even discov-

ered the echo of the initial fireball

which has cooled to a few degrees

above absolute zero

An even more shocking discovery

came at the end of the 20th century

By looking at supernova explosions

in the distant universe astronomers

discovered that the blasts did not

appear as bright as expected The conclusion The universal

expansion is accelerating In essence a long-range repulsive

force must be driving the universe to expand at ever greater

speeds As the Scottish geneticist J B S Haldane once famously

said ldquoThe universe is not only queerer than we imagine it is

queerer than we can imaginerdquo

Probingthe distantuniverse

F U N

Galaxies do not spreadevenly but gather in clustersthat themselves form vastfilaments leaving huge voidsin between

F A C T

Abell 1689

Thousands of galaxies cluster together in Abell 1689 The concentratioluminous matter and dark matter (stuff we canrsquot see but which adds to gity) creates a fun-house mirror of arcs and wisps NASAESATHE ACS SCIENCE TEA

F U N

For decades astronomershave known that the universecontains lots we canrsquot seeThis mysterious dark mattersurrounds galaxies and bindsclusters Scientists suspectexotic subatomic particlesare the culprit

F A C T




Dark ener

Atoms 5

Dark matter

F U N

Quasars mdash short for quasi-stellar radio sources mdash arethe brightest objects in theuniverse They radiate asmuch energy as an entire gal-axy from a volume no biggerthan our solar system

F A C T

F U N

Black holes are so dense thattheir gravity prevents evenlight from escaping Theyrange in size from monstersin galactic cores to star-sizedremnants of supernovaeSome scientists think thereeven may be mini-black holesleft over from the Big Bang

F A C T

Cosmic microwave background

The atoms that make up stars planets and us add up to just 5 percent of thuniverse Invisible dark matter makes up 23 percent more while the dark enthat drives the accelerating cosmos accounts for 72 percent ASTRONOMY ROEN K

The Great Attractor

The biggest concentration of matter in the nearby universe is a string ofhuge galaxy clusters known as the Great Attractor which is pulling the LoGroup and the Virgo cluster in its general direction EUROPEAN SOUTHERN OBSERV

The microwave background glows at a nearly constant temperature of 49deg above absolute zero Tiny variations in the glow are subtle density fluctuationthat gave rise to the galaxies and voids we see in the universe NASAWMAP SCIENC

What is the universe made of



Y

ou can make a connection to the universe at large

on any clear night Simply head outside and look up

You donrsquot need binoculars or a telescope (although

they wonrsquot hurt) mdash all you need are your eyes The

simplest thing to do is trace the patterns of stars Inwinter look for the commanding figure of Orion the Hunter

Spring brings the Big Dipper probably the most recognizable

stellar group in the sky

In the summertime look for the Northern Cross and trace the

path of the Milky Way which appears most prominent this time

of year The Great Square of Pegasus beckons on autumn eve-

nings You can find these patterns and from them hunt down

the less conspicuous constellations with the help of the circular

star map that appears at the center of every issue of Astronomy

Next use ldquoThe Sky this Monthrdquo in the magazine to home in

on the most visually arresting events in a given month It could

be a nice meteor shower where you might see a ldquoshooting starrdquoevery minute or so Or maybe therersquoll be a pretty conjunction

of the Moon with a bright planet or two (events like this usually

happen several times a month) Or perhaps yoursquoll be lucky and

get to witness a solar or lunar eclipse After all in the world of

backyard astronomy the sky is the limit

You and theuniverse

Conjunctions

Solar eclipses

When worlds align observers can expect a treat Here the Moon passes

front of the Sun blocking the brilliant solar disk and revealing the coronadisplays are possible because by cosmic coincidence the Sun is 400 timesfarther from Earth than the Moon and 400 times bigger than the Moon D

Lunar eclipses

A ruddy Moon signals a total lunar eclipse when the Moon dips completelyinto Earthrsquos shadow Earthrsquos atmosphere acts like a filter scattering out blue

When a crescent Moon passes a bright star or planet during the twilighhours itrsquos a sight that thrills any skywatcher experienced or not RANDALL

Meteor showers

Meteors storm from the sky at speeds of up to 44 miles per second Fric-tion with Earthrsquos atmosphere heats the tiny dust particles until they flare

Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14



Saturn

Mars

Marsrsquo ruddy appearance arisesbecause the sand on the planetrsquossurface consists largely of ironoxides mdash rust NASAJPLMSSS

Saturnrsquos rings consist of icy particlesranging in size from tiny motes tohouse-sized icebergs NASATHE HUBBLE

HERITAGE TEAM 983080STSCIAURA983081

F U N

Mars boasts the largest vol-canoes in the solar system

although theyrsquore all extinctThe biggest mdash OlympusMons mdash spans nearly 400miles and rises 13 milesabove the surrounding plain

F A C T

Earth may seem extraordinary to those who call it homebut itrsquos not a land of superlatives Earth is neither too hot

nor too cold too big nor too small Itrsquos just right in so

many ways mdash the perfect ldquoGoldilocksrdquo planet Of course

as the only known abode of life in the universe Earth

does have one major claim to being special The other planets in

the solar system leave their marks in different ways

The planets divide into two broad categories terrestrial and

jovian The small rocky terrestrial planets include Mercury

Venus Earth and Mars Mercury the closest to the Sun bakes

at temperatures up to 800deg Fahrenheit at noon But Mercuryrsquos

razor-thin atmosphere canrsquot hold heat at night the temperature

plummets far below freezing Venus most resembles Earth inmass and diameter but a thick atmosphere of carbon dioxide

has led to a runaway greenhouse effect Venusrsquo surface remains

a scorching 865deg F year-round

Earth and Mars are the water worlds of the solar system

Our home planet is the only one with liquid water at the surface

now but spacecraft observations during the past 15 years leave

no doubt that Mars once had loads of surface water Even now

Mars has permafrost and permanent polar caps of water ice

Winds up to 70 mph blow around the ubiquitous martian dust

creating shifting seasonal patterns

The jovian planets mdash Jupiter Saturn Uranus and Neptune

mdash are all gaseous behemoths They consist mostly of hydrogen

and helium the most abundant elements in the universe Jupiter

dwarfs the others It contains more than twice as much matter

as all the other planets combined All the jovian planets pos-

sess ring systems but only Saturnrsquos appears bright Its icy rings

span 170000 miles and measure just 100 feet thick Uranus

and Neptune are the true twin planets of the solar system with

nearly equal diameters masses compositions and rotations

Most scientists no longer consider small distant Pluto to be a

major planet A mixture of ice and rock this world more closely

resembles the thousands of so-called Kuiper Belt objects that

lurk beyond Neptune In 2006 astronomers demoted Pluto to a

ldquodwarf planetrdquo a category that also includes the asteroid Ceres

Planetsof thesolar system





Mercury 039 8797 days 0383 0055 5

Venus 072 22470 days 0949 0815 5

Earth 100 36526 days 1000 1000 5

Mars 152 68698 days 0532 0107 3

Ceres 277 460 years 0075 00002 1

Jupiter 520 1186 years 11209 317832 1

Saturn 958 2946 years 9449 95159 0

Uranus 1920 8401 years 4007 14536 1

Neptune 3005 16479 years 3883 17147 1




kel NASAJPLUSGS

Venus

Pluto amp Charon

Jupiter

ercury Earth

ranus Neptune








F U N



F A C T

F U N



F A C T








































Titan

Europa

Io









Moon Earth 238900 2732 2160 3






Dione Saturn 234500 274 698 1

Rhea Saturn 327500 452 949 1

Titan Saturn 759200 1595 3200 1

Iapetus Saturn 2212600 7933 913 1

Ariel Uranus 118600 252 719 1



Oberon Uranus 362600 1346 946 1


Major moons

ErosHale-Bopp

Callisto





F U N





Triton

nceladus



F U N



F A C T



Protostar

A








































Stars inour galaxy

The Sun



N49




F A C T

















Cone Nebula





F U N


F A C T



S c u t

u m - C

e n t a

u r u s

A r m

Norma Ar m

C e n t r a l b a r


r m

P e r s e

u s A

r m

O r i o n

S p u r

Sun

The MilkyWay Galaxy







name to our galaxy














isnrsquot possible)



















The Pleiades M3


F U N


F A C T









F U N


F A C T

F U N


F A C T



F U N


F A C T

F U N


F A C T



T








































Galaxies

in theuniverse

The Mice

NGC 4414



M87




M84 amp M86




NGC 68221760 kly


Draco Dwarf

248 kly MilkyWay

SMC189 kly

NGC 1852020 kly

NGC 1472460 kly

Andromeda Galax

2510 kly


2770 kly

Leo I818 kly

Leo II750 kly

Sextans

Dwarf 293 kly

LMC160 kly



F U N



F A C T


he LMC




F U N


F A C T

F U N


F A C T



H



























above absolute zero













F U N


F A C T

Abell 1689


F U N


F A C T




Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14




Mercury 039 8797 days 0383 0055 5

Venus 072 22470 days 0949 0815 5

Earth 100 36526 days 1000 1000 5

Mars 152 68698 days 0532 0107 3

Ceres 277 460 years 0075 00002 1

Jupiter 520 1186 years 11209 317832 1

Saturn 958 2946 years 9449 95159 0

Uranus 1920 8401 years 4007 14536 1

Neptune 3005 16479 years 3883 17147 1




kel NASAJPLUSGS

Venus

Pluto amp Charon

Jupiter

ercury Earth

ranus Neptune








F U N



F A C T

F U N



F A C T








































Titan

Europa

Io









Moon Earth 238900 2732 2160 3






Dione Saturn 234500 274 698 1

Rhea Saturn 327500 452 949 1

Titan Saturn 759200 1595 3200 1

Iapetus Saturn 2212600 7933 913 1

Ariel Uranus 118600 252 719 1



Oberon Uranus 362600 1346 946 1


Major moons

ErosHale-Bopp

Callisto





F U N





Triton

nceladus



F U N



F A C T



Protostar

A








































Stars inour galaxy

The Sun



N49




F A C T

















Cone Nebula





F U N


F A C T



S c u t

u m - C

e n t a

u r u s

A r m

Norma Ar m

C e n t r a l b a r


r m

P e r s e

u s A

r m

O r i o n

S p u r

Sun

The MilkyWay Galaxy







name to our galaxy














isnrsquot possible)



















The Pleiades M3


F U N


F A C T









F U N


F A C T

F U N


F A C T



F U N


F A C T

F U N


F A C T



T








































Galaxies

in theuniverse

The Mice

NGC 4414



M87




M84 amp M86




NGC 68221760 kly


Draco Dwarf

248 kly MilkyWay

SMC189 kly

NGC 1852020 kly

NGC 1472460 kly

Andromeda Galax

2510 kly


2770 kly

Leo I818 kly

Leo II750 kly

Sextans

Dwarf 293 kly

LMC160 kly



F U N



F A C T


he LMC




F U N


F A C T

F U N


F A C T



H



























above absolute zero













F U N


F A C T

Abell 1689


F U N


F A C T




Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14








































Titan

Europa

Io









Moon Earth 238900 2732 2160 3






Dione Saturn 234500 274 698 1

Rhea Saturn 327500 452 949 1

Titan Saturn 759200 1595 3200 1

Iapetus Saturn 2212600 7933 913 1

Ariel Uranus 118600 252 719 1



Oberon Uranus 362600 1346 946 1


Major moons

ErosHale-Bopp

Callisto





F U N





Triton

nceladus



F U N



F A C T



Protostar

A








































Stars inour galaxy

The Sun



N49




F A C T

















Cone Nebula





F U N


F A C T



S c u t

u m - C

e n t a

u r u s

A r m

Norma Ar m

C e n t r a l b a r


r m

P e r s e

u s A

r m

O r i o n

S p u r

Sun

The MilkyWay Galaxy







name to our galaxy














isnrsquot possible)



















The Pleiades M3


F U N


F A C T









F U N


F A C T

F U N


F A C T



F U N


F A C T

F U N


F A C T



T








































Galaxies

in theuniverse

The Mice

NGC 4414



M87




M84 amp M86




NGC 68221760 kly


Draco Dwarf

248 kly MilkyWay

SMC189 kly

NGC 1852020 kly

NGC 1472460 kly

Andromeda Galax

2510 kly


2770 kly

Leo I818 kly

Leo II750 kly

Sextans

Dwarf 293 kly

LMC160 kly



F U N



F A C T


he LMC




F U N


F A C T

F U N


F A C T



H



























above absolute zero













F U N


F A C T

Abell 1689


F U N


F A C T




Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14





Moon Earth 238900 2732 2160 3






Dione Saturn 234500 274 698 1

Rhea Saturn 327500 452 949 1

Titan Saturn 759200 1595 3200 1

Iapetus Saturn 2212600 7933 913 1

Ariel Uranus 118600 252 719 1



Oberon Uranus 362600 1346 946 1


Major moons

ErosHale-Bopp

Callisto





F U N





Triton

nceladus



F U N



F A C T



Protostar

A








































Stars inour galaxy

The Sun



N49




F A C T

















Cone Nebula





F U N


F A C T



S c u t

u m - C

e n t a

u r u s

A r m

Norma Ar m

C e n t r a l b a r


r m

P e r s e

u s A

r m

O r i o n

S p u r

Sun

The MilkyWay Galaxy







name to our galaxy














isnrsquot possible)



















The Pleiades M3


F U N


F A C T









F U N


F A C T

F U N


F A C T



F U N


F A C T

F U N


F A C T



T








































Galaxies

in theuniverse

The Mice

NGC 4414



M87




M84 amp M86




NGC 68221760 kly


Draco Dwarf

248 kly MilkyWay

SMC189 kly

NGC 1852020 kly

NGC 1472460 kly

Andromeda Galax

2510 kly


2770 kly

Leo I818 kly

Leo II750 kly

Sextans

Dwarf 293 kly

LMC160 kly



F U N



F A C T


he LMC




F U N


F A C T

F U N


F A C T



H



























above absolute zero













F U N


F A C T

Abell 1689


F U N


F A C T




Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14



Protostar

A








































Stars inour galaxy

The Sun



N49




F A C T

















Cone Nebula





F U N


F A C T



S c u t

u m - C

e n t a

u r u s

A r m

Norma Ar m

C e n t r a l b a r


r m

P e r s e

u s A

r m

O r i o n

S p u r

Sun

The MilkyWay Galaxy







name to our galaxy














isnrsquot possible)



















The Pleiades M3


F U N


F A C T









F U N


F A C T

F U N


F A C T



F U N


F A C T

F U N


F A C T



T








































Galaxies

in theuniverse

The Mice

NGC 4414



M87




M84 amp M86




NGC 68221760 kly


Draco Dwarf

248 kly MilkyWay

SMC189 kly

NGC 1852020 kly

NGC 1472460 kly

Andromeda Galax

2510 kly


2770 kly

Leo I818 kly

Leo II750 kly

Sextans

Dwarf 293 kly

LMC160 kly



F U N



F A C T


he LMC




F U N


F A C T

F U N


F A C T



H



























above absolute zero













F U N


F A C T

Abell 1689


F U N


F A C T




Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14
















Cone Nebula





F U N


F A C T



S c u t

u m - C

e n t a

u r u s

A r m

Norma Ar m

C e n t r a l b a r


r m

P e r s e

u s A

r m

O r i o n

S p u r

Sun

The MilkyWay Galaxy







name to our galaxy














isnrsquot possible)



















The Pleiades M3


F U N


F A C T









F U N


F A C T

F U N


F A C T



F U N


F A C T

F U N


F A C T



T








































Galaxies

in theuniverse

The Mice

NGC 4414



M87




M84 amp M86




NGC 68221760 kly


Draco Dwarf

248 kly MilkyWay

SMC189 kly

NGC 1852020 kly

NGC 1472460 kly

Andromeda Galax

2510 kly


2770 kly

Leo I818 kly

Leo II750 kly

Sextans

Dwarf 293 kly

LMC160 kly



F U N



F A C T


he LMC




F U N


F A C T

F U N


F A C T



H



























above absolute zero













F U N


F A C T

Abell 1689


F U N


F A C T




Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14



S c u t

u m - C

e n t a

u r u s

A r m

Norma Ar m

C e n t r a l b a r


r m

P e r s e

u s A

r m

O r i o n

S p u r

Sun

The MilkyWay Galaxy







name to our galaxy














isnrsquot possible)



















The Pleiades M3


F U N


F A C T









F U N


F A C T

F U N


F A C T



F U N


F A C T

F U N


F A C T



T








































Galaxies

in theuniverse

The Mice

NGC 4414



M87




M84 amp M86




NGC 68221760 kly


Draco Dwarf

248 kly MilkyWay

SMC189 kly

NGC 1852020 kly

NGC 1472460 kly

Andromeda Galax

2510 kly


2770 kly

Leo I818 kly

Leo II750 kly

Sextans

Dwarf 293 kly

LMC160 kly



F U N



F A C T


he LMC




F U N


F A C T

F U N


F A C T



H



























above absolute zero













F U N


F A C T

Abell 1689


F U N


F A C T




Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14



F U N


F A C T

F U N


F A C T



F U N


F A C T

F U N


F A C T



T








































Galaxies

in theuniverse

The Mice

NGC 4414



M87




M84 amp M86




NGC 68221760 kly


Draco Dwarf

248 kly MilkyWay

SMC189 kly

NGC 1852020 kly

NGC 1472460 kly

Andromeda Galax

2510 kly


2770 kly

Leo I818 kly

Leo II750 kly

Sextans

Dwarf 293 kly

LMC160 kly



F U N



F A C T


he LMC




F U N


F A C T

F U N


F A C T



H



























above absolute zero













F U N


F A C T

Abell 1689


F U N


F A C T




Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14



T








































Galaxies

in theuniverse

The Mice

NGC 4414



M87




M84 amp M86




NGC 68221760 kly


Draco Dwarf

248 kly MilkyWay

SMC189 kly

NGC 1852020 kly

NGC 1472460 kly

Andromeda Galax

2510 kly


2770 kly

Leo I818 kly

Leo II750 kly

Sextans

Dwarf 293 kly

LMC160 kly



F U N



F A C T


he LMC




F U N


F A C T

F U N


F A C T



H



























above absolute zero













F U N


F A C T

Abell 1689


F U N


F A C T




Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14



NGC 68221760 kly


Draco Dwarf

248 kly MilkyWay

SMC189 kly

NGC 1852020 kly

NGC 1472460 kly

Andromeda Galax

2510 kly


2770 kly

Leo I818 kly

Leo II750 kly

Sextans

Dwarf 293 kly

LMC160 kly



F U N



F A C T


he LMC




F U N


F A C T

F U N


F A C T



H



























above absolute zero













F U N


F A C T

Abell 1689


F U N


F A C T




Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14



H



























above absolute zero













F U N


F A C T

Abell 1689


F U N


F A C T




Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14



Dark ener

Atoms 5

Dark matter

F U N


F A C T

F U N


F A C T



The Great Attractor






Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14



Y





















You and theuniverse

Conjunctions

Solar eclipses



Lunar eclipses



Meteor showers


Annual showers

Name Peak date

Quadrantids Jan 3

Lyrids April 22

Eta Aquarids May 6

Perseids Aug 12

Orionids Oct 21

Leonids Nov 17

Geminids Dec 14

your guide to planets stars and galaxies

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