your guide to the

an astronomyinformation resource

for primary schools

universe

The South African Agency for Science andTechnology Advancement is funding thisbooklet as information resource for a nationalASTRONOMY QUIZ. The material should beused by learners who prepare to take part inthe Astronomy Quiz, together with furtherinformation and links published on theSAASTA website: www.saasta.ac.za

Various sources were used to compile theinformation contained in this booklet.They include: Exploring our origins - SKA South Africa(www.ska.ac.za); The Kingfisher Visual Fact Finder; The Oxford Children's Encyclopedia;www.saao.ac.za; www.ska.ac.za; www.hartrao.ac.za;http://kids.msfc.nasa.gov/; http://kidsastronomy.com; www.womanastronomer.com;

For solar system information,visit the website: www.nineplanets.org.

The Solar System 2The Sun 3The Planets 4Mercury 5Venus 6Earth 7Mars 8Asteroids 8Jupiter 9Saturn 10Uranus 12Neptune 13Pluto 14The Moon 15Meteoroids and Meteorites 16Comets 16Stars 17Black Holes 17Galaxies 18The Universe 18Space Exploration 19Uses of Satellites 19Space Exploration Fact file 20South Africa and Space Exploration 21Famous Astronomers 22Famous Women Astronomers 23Women Astronomers in South Africa 23South African Astronomers in History 23Astronomy in South Africa 24Radio Astronomy 26The Square kilometre Array Telescope 27Space Geodesy 28

2

THE SOLAR SYSTEMThe Sun is an ordinary star, just like the onesyou can see twinkling in the sky at night. Butfor us and all the creatures and plants that liveon Earth, the Sun is very special.

The Sun is the centre of our Solar System.Orbiting around the Sun is its family of majorplanets, many with their own moons. Thereare also dwarf planets and thousands of othersmaller objects such as asteroids, comets andmeteor streams. The strong pull of the Sun'sgravity holds it all together.

The Solar System is huge - over 12 000million kilometres in diameter. It is shaped likean almost flat disk, as all the planets orbitin roughly the same plane. Pluto's orbit istilted a little to the rest, and it also crosses justinside Neptune's orbit.

Our Sun is just one of about 100 000million stars that make up our Milky Waygalaxy. The Milky Way is one of many suchstar systems, each of which is called a galaxy.The Universe consists of about 100 000million galaxies, each containing their ownstars, planets and clouds of gas and dust, outof which stars and planets are born.

Day and nightEvery day we see the Sun rise in the east andset in the west. For thousands of years, peo-ple thought that the Sun traveled around theEarth. Today we know that the Earth travelsaround the Sun. As the Sun shines on the Earth, the rotation

of the Earth around its own axis every24 hours produces day and night. Thisrotation makes it seem like the Sun is movingacross the sky.

The seasonsThe movement of the Earth in an almost perfectcircle around the Sun takes 365.26 days.Together, these days produce our year on Earth.

The seasons – Spring, Summer, Autumn andWinter – occur because the Earth's rotation axisis tilted at 23.5˚ to the plane of its orbit aroundthe Sun. This means that for six months of theyear from September through March the southernhemisphere is tilted towards the Sun, the tilt beingbiggest in December during mid-summer. InSouth Africa at this time we get lots of heat fromthe Sun because it passes nearly overhead atmid-day, and days are long. For the other sixmonths from March through September, thesouthern hemisphere is tilted away from the Sun,the tilt being biggest in June, when we experi-ence mid-winter. At this time we get much lessheat from the Sun because at mid-day it is onlyabout half-way up from the horizon, and daysare short.

The Solar System consists of:H The SunH Eight planetsH Five dwarf planetsH Many moons orbiting the planets and

dwarf planetsH Thousands of small Solar System bodiesH Interplanetary dust

Image not to scale

3

The SunThe Sun's heat and light provide the energyfor life to exist on Earth. The Sun is a giantball of extremely hot hydrogen and heliumgases, nearly 150 million kilometres away.It is gigantic compared to the Earth. If youthink of the Sun as a football, Earth wouldbe the size of the head of a match. Youcould fit about 100 Earths side by sideacross the Sun and it could hold more thana million Earths inside its volume. Onlybecause the Sun is so far away does itappear to be the same size in the sky as ourour Moon, which is actually much smallerthan our Earth, but much closer to Earth thanthe Sun is.

The Sun is extremely hot. On the surfaceof the Sun the temperature is nearly 6000degrees Celsius, but at the centre it is about

16 million degrees. In this hot, dense coreof the Sun hydrogen atoms get squashedinto each other to produce helium atoms.This releases enormous amounts of energy,which escapes as heat and light. The Sunalso produces X-rays and ultraviolet raysthat are harmful to life, but most of theserays get soaked up by the Earth's atmos-phere and do not harm us.

Scientific research has shown that theSun and planets formed about 4.6 billionyears ago out of a big cloud of gasand dust. All the planets, asteroids andcomets that orbit the Sun, including theEarth, formed at the same time.Sometimes dark spots, called sunspots,appear on the surface of the Sun. Theseare cooler areas and are produced bystrong magnetic fields.

WARNING!Never look directly at the

Sun. It is even moredangerous to look at the Sunthrough a pair of binocularsor a telescope. You will beblinded for life! Don't even

look at the Sun throughsunglasses.

Burning outThe Sun will burn out oneday. It is predicted that

when the Sun reaches theend of its life, it will swell upto a few hundred times itscurrent size. It might just be

big enough to engulf/swallow the Earth. But this isno reason for concern, sinceit will take another 5 billion

years for it to happen!

4

THE PLANETSAlthough all the planets of our Solar Systemwere formed at the same time and from thesame cloud of gas and dust, there are greatdifferences between them.

The four inner terrestrial (Earth-like) planetsare Mercury, Venus, Earth and Mars, andare mainly made of rock and metal. Beyondlie Jupiter, Saturn, Uranus and Neptune,which are giant, gas planets. Distant dwarfplanets do not fit into any of these groups.They are probably made of ice and rock.

Remember the planetsThe planets are named after ancientGreek and Roman gods. An easy way toremember these names is to remember thesentence: “Mother very enthusiastically madea jelly sandwich under no protest” or ”ManyVery Elderly Men Just Sleep UnderNewspapers” or “My Very Excellent MotherJust Served Us Noodles” or “Mary's VioletEyes Make John Stay Up Nights”.

Beginning with Mercury, the closest to theSun, and ending with Neptune, the farthestfrom the Sun, the sentence gives you clues tothe order of the planets: Mercury, Venus,Earth, Mars, Asteroids, Jupiter, Saturn,Uranus, Neptune.

Dwarf PlanetsPluto, which used to be the ninthplanet, and many other similar sizedbodies lie beyond Neptune. In 2003,Eris was discovered, which is largerthan Pluto. In 2006 the InternationalAstronomical Union created a newcategory of solar system objectscalled “dwarf planets” that is distinctfrom “planets”. Pluto was reclassified asa dwarf planet, Eris received dwarfplanet status and Ceres, the largest ofthe asteroids that orbit mainly betweenMars and Jupiter, was also classified asa dwarf planet.

Another two objects lying beyondNeptune, called Haumea and Makemake,have also been classified as dwarfplanets.There could be about 200objects, in this region called the KuiperBelt, which may be big enough to becalled dwarf planets. It is likely thatthere will be many more dwarf planetsin the future as the sky is more fullyexplored. All of the dwarf planets thatwe know of so far are smaller than ourMoon. The definition of a “dwarf planet” is:a celestial body that a. is in orbit around the Sun, b. has sufficient mass to become

nearly round in shape, c. has not cleared its orbit of other

celestial bodies, and d. is not a satellite (or moon) of

another celestial body.The celestial bodies that are not massiveenough to be rounded by their owngravity are called “small solar systembodies”.

5

MERCURYMercury is the closest planet to the Sun.It was named after the Roman god, Mercury,the messenger of the other gods. It is thesmallest of the eight planets.

Mercury's year is shorter than its day!This planet has the shortest year in the SolarSystem – only 88 days – but sunrise to

sunrise on Mercury takes Earth 176 days(almost six months).

During its daytime, its surface becomesextremely hot and at night its surface is icycold. It is covered with mountains, valleysand craters and looks like our Moon.Humans would not be able to live onMercury.

Mercury fact file

Diameter: 4880 km, about the size of the Earth's Moon.Mean distance from the Sun: 58 million kmDay/night: 176 Earth daysLength of year: 88 Earth daysTemperature: -185˚C to 467˚CSatellites: 0

6

VENUSVenus is the hottest planet in the Solar System.It was named after the Roman goddess of loveand beauty because it looks like a gleaminggem in the sky. But in fact, the planet is a hot,rocky waste under an atmosphere almostentirely made up of carbon dioxide. Its thickatmosphere holds in the Sun's heat.

Venus and the Earth are almost the samesize. Venus is also the planet that approachesclosest to Earth.

The surface of Venus is completelyhidden by dense, white clouds. However,we know what its surface looks likethanks to information we got from spaceradar, and two spacecraft that landedon its surface and took pictures. There arehigh mountains, craters and volcanoes onVenus.

Venus is unusual because it rotates inthe opposite direction from all the otherplanets.

Venus fact file

Diameter: 12 104 km, about 0,8 times the size of the EarthMean distance from the Sun: 108 million kmDay/night: 117 Earth daysLength of year: 225 Earth daysTemperature: 460˚C on averageSatellites: 0

7

EARTHOur planet is the largest of the rocky (terrestrial= Earth-like) planets. The word “earth” is OldEnglish and comes from German. As far aswe know, the Earth is unique in the SolarSystem for two reasons: it has liquid wateron its surface and it supports life. If you lookat Earth from space it seems like a blue andwhite ball. Before the time of space traveland satellite images, people were not ableto see Earth like this. Without pictures itis hard to imagine that the Earth is aball-shaped planet traveling through space.

Earth is almost round like a ball, but notquite. It bulges at the middle (Equator) andflattens at the Poles. This shape is called aspheroid.

The time its takes the Earth to completeone orbit around the Sun is called a year.A year is 365 days, 5 hours, 48 minutesand 46 seconds long. We divide the yearinto 365 days, but every fourth year, a leapyear, has 366 days to make up the extratime. In a leap year there are 29 days inFebruary.

Earth fact file

Diameter: 12 756 kmMean distance from the Sun: 150 million kmDay/night: 24 hoursLength of year: 365 Earth days 5 hoursTemperature: maximum 58˚C; minimum -89˚CSatellites: 1 – the Moon

MarsMars was named after the Roman god of warand agriculture. It shines very brightly whenclosest to the Earth, but at other times its orbittakes it so far away that it is much dimmer, likea star. It has a orange-red colour and so isoften called the Red Planet.

Mars is the only planet selected forpossible exploration by humans becauseconditions there are more like those onEarth than on any of the other planets.There is evidence that Mars once hadrivers, streams, lakes, and even an ocean.Today the only water on Mars is eitherfrozen in its polar caps, or underground.

In recent years, unmanned spacecraft calledspace probes have landed on Mars. Theprobes, sent to Mars by the United States ofAmerica, performed experiments on thesurface and atmosphere. The dirt was foundto contain clay rich in iron.

Mars has many craters and mountains.The highest mountain peak and some of thedeepest valleys in the Solar System are foundon Mars.

Mars has two moons, called Deimos andPhobos. They might be the remnants of alarger moon that broke up many millions ofyears ago, but they could well be asteroidsthat have been captured by Mars.

AsteroidsAsteroids are minor planets. Many of themare found in a belt between Mars and Jupiter.Being small, they look like pinpoints of light inthe night sky. Over 3000 have been discov-ered, but you need not know all their names!The largest known is Ceres, which has adiameter of 1000 km. Smaller asteroids arenot round, but have irregular shapes, likepotatoes.

Asteroids are bits of rock. They are leftover material from the time our Sun its andplanets were formed.

Today about 1000 asteroids orbit nearthe Earth. Asteroids have on occasioncollided with the Earth to form very large

impact craters. The largest in the world can befound around Vredefort in the Free State,100km south of Johannesburg.It occurred 2 bil-lion years ago. The crater was much biggerthan the 85km wide ring of hills that we nowsee around Vredefort. It has been worn awayby erosion over time. Tswaing, 40km north ofTshwane, is a 1 km wide crater made just 200000 years ago by an asteroid the size of a build-ing. Have you visited either of them?

Mars fact file

Diameter: 6 794 km, about half that of the EarthMean distance from the Sun: 228 million kmDay/night: 24 hours 37 minutesLength of year: 687 Earth daysTemperature: -133˚C to +27˚C Satellites: 2

The Tswaing meteor crater. Photo: M J Gaylard

9

JupiterIn mythology, Jupiter (known as Zeus inGreece) was the king of the gods. Jupiter isby far the largest planet in the SolarSystem. It is so big that all the other planetscan be squeezed inside it.

Jupiter spins so fast that a day on theplanet lasts less than 10 hours.

Jupiter is made up of about 90% hydro-gen and 10% helium, with traces of otherelements. In its centre these gases arecompressed to a very hot liquid. Thestripes on its surface are cloud markings.Large areas of swirling gases can be

found in Jupiter' atmosphere. The largest of theseis called the Great Red Spot. Scientists have beenwatching this giant storm rage for several hundredyears. Bolts of lightning have also been seen inJupiter's atmosphere.

Photographs taken by spacecraft have shownthin, dark rings around Jupiter.

By 2003, 63 moons had been found orbitingJupiter. The four largest moons were discovered byGalileo Galilei with his primitive telescope in 1610.They are Io, Europa, Ganymede and Callisto. Thereare active volcanoes on Io, which orbits Jupiter in aday. Europa is a ball of ice. Ganymede is thelargest satellite in the Solar System.

Jupiter fact file

Diameter:142 800 kmMean distance fromthe Sun: 778 million kmDay/night:9 hours 50 minutesLength of year:4330 Earth days = 11.9 Earth yearsTemperature: -150˚C Satellites: 63 discoveredby 2009

1110

Saturn fact file

Diameter: 120 000 kmMean distance from the Sun: 1429 million kmDay/night: 10 hours 14 minutesLength of year: 10759 Earth days = 29.5 Earth yearsTemperature: -170˚C Satellites: 61 (as of 2009)

SaturnSaturn gets its name from the Roman god ofagriculture. It is the second largest planet inthe Solar System. Saturn is known as theringed planet. We now know that all fourgiant planets have rings, but Saturn's are byfar the most impressive.

Saturn has over 1000 rings, made ofice and dust. The ice particles in therings range from pebble-size to housesize. Scientists think these rings could bethe remains of a small moon or moonsthat were smashed by comets ormeteorites. Saturn's gravity could thenhave pulled the particles into rings.

Saturn is a very large gas planet whichspins so quickly that its equator bulgesoutward and the top and bottom areflattened out noticeably. The white spots onSaturn's surface are powerful storms.

Saturn has a lot of moons (61 discoveredas of 2009) of which 52 have beennamed. Titan is Saturn's biggest moon andit has a thick nitrogen atmosphere.

In January 2005, the Huygens space craftplunged through Titan's atmosphere andsent back to Earth the first images of this,the furthest place from Earth a spacecrafthas ever landed. Scientists think thatconditions on Titan are like those on Earth4.6 billion years ago.

The mysteries of Saturn have alwayspuzzled researchers. They wonder whySaturn, a gas-giant made up primarily ofhydrogen and helium, releases moreenergy than it absorbs from faint sunlight.Titan is also the only moon in the solarsystem to have a dense atmosphere, oneeven thicker than Earth's.

Here are the names of 30 ofSaturn's moons. Try and find themin this word puzzle:

MimasHyperionEpimetheusYmirThrymEnceladusIapetusJanusPaaliaqSkadiTethysPanCalypsoSiarnaqMundilfari

DioneAtlasTelestoTarvosErriapoRheaPrometheusHeleneKiviuqAlbiorixTitanPandoraPhoebeIjiraqSuttung

AM U N D I L F A R I C D E G FI T A I E N C E L A D U S I H

M T R J A N U S T P H O E B EA U O I K L M L H E L E M E PS N D R J N A P Q T H R Y M IO G N A R S A K S U T V M H MU B A Q A N R A I S W X I Y EO S P Y L A C L C V K D R P TT I T A N S Y B D Z I A E E HS F H G Y S T I U H I U D R EE J L H K O O O M N L X Q I UL P T R Q N V R H E A W Y O SE E A C E R R I A P O B D N ET A R V O S Z X P A A L I A Q

S U E H T E M O R P B N A P

12

UranusIn mythology, Uranus was the lord of theskies and the husband of Earth. Apartfrom the fact that it orbits the Sun on itsside and has satellites, little was knownabout this planet until the space probeVoyager 2 flew past it 20 years ago.

Uranus' odd tilt may be the result of apowerful crash with another large objectsoon after it had formed. The effect is thateach pole spends about 40 years in

constant summer sunlight, and then another40 years in winter darkness.

Uranus has many dark rings - nine major onesand many other faint ones. The planet itself ismade up mainly of hydrogen and helium gases.It has a rocky core and there may be an ocean ofwater/ammonia beneath its clouds.

Uranus has at least 27 moons, most namedafter characters in Shakespeare plays. The largestones are Titania, Ariel and Miranda.

Uranus fact file

Diameter: 51 000 kmMean distance from theSun: 2870 million kmDay/night:17 hours 14 minutesLength of year:30685 Earth days = 84 Earth yearsTemperature: -200˚C Satellites: 27 discovered by 2009

13

NeptuneNeptune was named after the Roman god ofwater and the ocean. Its bright blue atmos-phere, coloured by methane, might look calm,but Voyager 2 discovered winds of up to2000 km/h ripping through its atmosphere -the fiercest winds in the Solar System.The winds travel in a different direction to theplanet's spin.

Neptune has a large storm raging on itssurface, much like Jupiter. It is called the

Great Dark Spot. This storm, discovered byVoyager 2, is large enough to contain theEarth.

Neptune has four rings surrounding it. It isthe outermost giant planet. It is the outer-most planet.

It also has at least thirteen moons, six ofthem discovered by Voyager 2. Many moremay still be discovered. The largest ofNeptune's moons, Triton orbits Neptunebackwards.

Neptune fact file

Diameter: 49 500 kmMean distance from theSun: 4504 million kmDay/night:17 hours 6 minutesLength of year:60190 Earth days = 165 Earth yearsTemperature: -210˚C Satellites: 13 discoveredby 2009

14

Pluto fact file

Diameter: 2 300 kmMean distance from the Sun: 5900 million kmDay/night: 6 Earth days and 9 hoursLength of year: 90550 Earth days = 248 Earth yearsTemperature: -230˚C Satellites: Three known by 2009

PlutoPluto, now classified as a dwarf planet, wasnamed after the mythological god of the under-world. It was discovered by Clyde Tombaugh in1930 and we still know very little about it. It wasoriginally thought to be as big as the Earth andso was called a planet for many years. It is toofar away to see in detail with a telescope.The first space probe intended to explore it waslaunched in 2006.

Pluto has one large moon, called Charon,which is about half the size of its parent body,Pluto. Some astronomers call Pluto and Charona double dwarf planet because they are soclose in size. In addition, two small moonswere discovered in 2005.

Pluto has an unusual orbit around theSun. It usually is further from the Sun thanNeptune, but once every 248 yearsPluto swings inside the orbit of Neptune.It stays there for 20 years. During thistime, Pluto is closer to the Sun thanNeptune.

While it is closer to the Sun, scientiststhink that Pluto might develop an atmos-phere. They reason that methane andnitrogen frozen at its poles will thaw outand rise temporarily to form the atmos-phere. But when Pluto moves back furtherfrom the Sun, they think its atmospherewill freeze again.

15

MoonThe Moon is the Earth's satellite. It is a rockybody orbiting our planet at a mean distance of384 000 kilometres. Like the planets, it producesno light of its own, but we can see it becauseit reflects the light from the Sun. The shape thatwe see depends on where the Moon is in itsorbit around the Earth. You can see the Moonclearly with the naked eye and even better withbinoculars. You always see the same side of theMoon from Earth.

The Moon's surface has many craters,formed by large bodies such as comets andasteroids that crashed into it between 3 and 4billion years ago. Apart from the craters, theMoon's surface is like a desert with plains,

mountains and valleys. The Moon has noatmosphere, so there is no air to breathe,and no wind or weather. Recently, waterice was discovered at the poles of theMoon, buried beneath dust on the surface.

The Moon is the only place in our SolarSystem, other than the Earth, where humanshave visited. On 20 July 1969 astronautsNeil Armstrong and Edwin Aldrin landedthe Lunar Module of Apollo 11 on theMoon's surface. Armstrong became the firstperson to set foot on the Moon. A total oftwelve astronauts landed on the Moonbetween 1969 and 1972. There are plansto develop new spacecraft so that humanscan once again go to the Moon.

Moon fact file

Diameter: 3 476 kmMean distance fromEarth: 380 000 kmDay/night:29.5 Earth daysTemperature: -170˚C;maximum: 110˚C

16

METEOROIDS AND METEORITESMeteorites are rocks from space that strikethe Earth.

Meteoroids are small stone or metallicrocks. Small ones form when comets (seebelow) come near the Sun. Small particlesare thrown out by the comet by the million.They travel in the comet's orbit in hugeswarms, but are invisible themselves. Largemeteoroids come from the asteroid belt.

When a meteoroid enters the Earth'satmosphere it is travelling very fast. It willheat up and burn brightly. It is then calleda meteor. We commonly call the streak oflight it produces a “shooting star”. A bigmeteoroid will produce a fireball.

Most of theoriginal meteorwill burn upbefore it strikesthe surface of theEarth. Any meteorlarge enough totravel through theEarth's atmos-phere and hit theground is calleda meteorite.

Ordinarymeteors burn upat a height of about 50 km from the Earth'ssurface. Larger ones (bigger than a smallstone) may explode, and pieces may landon the Earth as meteorites.

COMETSComets are lumps of ice and rock that travel fromthe far outer Solar System to orbit our Sun. As thecomet nears the Sun, the ice melts and gives offgas jets and clouds of dust. We see this as adramatic tail, shining in reflected sunlight. Such atail can stretch for many millions of kilometres.

A comet's tail (rock particles and melting ice) isforced away from its nucleus by solar winds. Thetail of the comet can therefore be either behindor in front of it, depending on its position inrelation to the Sun. A comet's tail always pointsaway from the Sun.

Some comets take thousands of years to goaround the Sun, while others take only a fewyears. Probably the most famous comet of all isHalley, which returns every 76 years.

Comets are usually named after the personwho discovers them. Halley's Comet was namedafter Edmund Halley (1656 - 1742), an Englishscientist.

17

STARSStars are shining balls of gas.Their heat comes from deepinside, where hydrogen gas isturned into helium, giving outenergy. Our Sun is the star weknow best. Stars like the Sunhave a relatively low mass. Theyshine steadily for billions ofyears before they burn out.

A star is formed when part ofa cloud of gas and dust collaps-es. When the gas cloud drawsitself into a dense blob, the tem-perature in the centre rises to mil-lions of degrees Centigrade. Atthese temperatures, a nuclearreaction starts which gives offlight … and a star is born, oftenwith new planets orbitingaround it. By April 2009, almost350 planets had been discov-ered around other nearby stars.

When a star burns out, its cen-tral core collapses, shrinkingdown to the size of the Earthand it becomes a “white dwarf”star. One teaspoon of whitedwarf material weighs as muchas 5 tons! As its core collapses,

the star's outer layers will expandand will finally be expelled in avery fast stellar wind, forming abeautiful planetary nebula.

Some stars can be up to 100times as massive as the Sun, withmuch shorter lives, measured inmillions of years.

Stars vary in temperature,brightness and size. Some arevery hot and shine with a bluishlight, while others are much coolerand look orange or red. Thesecolours can be seen with thenaked eye in some stars. Our Sunis an average star, slightly yellowin colour.

The brightness of a star as wesee it depends on the type of staras well as its distance from theEarth. The brightest star in thesky is not the closest one to us.It is called Sirius and is muchwhiter and hotter than the Sun.The closest star to us after theSun is called Proxima Centauri.It is small, dim and red.The astronomer Robert Innesdiscovered it from Johannesburgin 1915. It is the closest star toEarth (after our Sun).

Black holesWhen a massive star dies, it explodes as a“supernova” which can be bright enough tosee during the day. Many leave behind acore a little more massive than the Sun, thatcollapses down into a neutron star - the small-est, densest of stars, only about 30 km in

diameter. One pinhead of such neutron starmaterial would weigh about one milliontons!

If the collapsing core is massive enough,its gravity becomes so strong that no lightcan escape from it, producing a “blackhole”.

A Hubble Space Telescopeimage of the very stunningplanetary nebula called theCat-Eye Nebula (NGC6543).The dying central star possiblyproduced this simple, outerpattern of dusty concentricshells by ejecting its outerlayers in a series of regularconvulsions. The formation ofthe beautiful, more complexinner structures is not wellunderstood though. Credit: NASA, ESA, HEIC, andThe Hubble Heritage TeamcI/AURA). Taken fromAstronomy Picture of the Day.

GALAXIESGalaxies are a collection of gas, dust and avast number of stars. They are generally eitherspiral, round like a soccer ball, elliptical like arugby ball, or irregular in shape. Dwarf galax-ies may contain a few million stars and giantgalaxies can contain billions of stars.

Our Sun is one of the stars in the Milky Waygalaxy. The Milky Way, a spiral galaxy, ismade up of over 100 billion stars. On aclear, dark night you can see the Milky Way.It looks like a hazy band across the sky. Thehazy light is actually from billions of stars sofar away that to our eyes their light blurstogether. Telescopes however, show that itreally is stars producing the light.

The Andromeda galaxy is the nearest majorgalaxy to our own Milky Way galaxy. Theyare similar in size and shape, and both havea number of dwarf galaxies orbiting them.

Galaxies often exist in groups. Ourgalaxy belongs to a group of galaxiescalled the Local Group. Astronomers havediscovered many thousands of other groupsof galaxies in the Universe.

THE UNIVERSEPeople used to believe that the Earth was thecentre of the Universe with everything elserevolving around it. Now we know our planetis only one part of one small system. Our Sunis just one of billions of stars in our galaxy.Our galaxy and countless others like it makeup the Universe.

The Universe is changing and getting big-ger all the time. The American astronomerEdwin Hubble (1889 - 1953) was the first todiscover that the galaxies are moving awayfrom each other. He also discovered that thefarther away a galaxy is, the faster it seemsto be moving. The explanation for this is thatspace itself is expanding.

If space is expanding, it means that every-thing in space must once have been squashedtogether in a small, incredibly dense ball.Astronomers believe this ball started expanding

about 14 000 million years ago, in whatthey call the Big Bang. This marked thebeginning of the Universe as we know it.

Cosmology is the study of how theUniverse began and how it will be in future.The Universe may go on getting bigger forever. But it is also possible that the galaxiesmay come together and draw back into oneplace until they collide and rush together intothe “Big Crunch”. Scientists will continue todiscuss this topic for many years.

19

SPACE EXPLORATIONFor many centuries, space explorationseemed like a fantastic dream. To leavethe Earth behind one has to build anengine powerful enough to travel at11 kilometres per second. This is thespeed that beats the pull of the Earth'sgravity. In the twentieth century, theinvention of powerful rockets made spacetravel possible.

A man-made satellite is a spacecraftplaced in orbit around a planet.Thousands of satellites have beenlaunched and are currently in orbitaround the Earth, where they gather infor-mation about the Earth and the Universe.

USES OF SATELLITESSatellites are launched into space to do aspecific job. Some examples:H Remote sensing satellites carry cameras

that take pictures of the Earth.H Weather satellites take pictures to

help experts predict weather patternsand their movements.

H Navigation satellites carry specialtransmitters to help people work outexactly where they are.

H Communication satellites bouncemessages such as telephone calls,television images and Internetinformation from one side of the worldto the other.

H Space tourism satellites transport,transfer and care for people who wantto holiday in space. This is a relativelynew idea and only affordable to thesuper rich.

H Military satellites are used for spyingor to guide missiles.

(Information kindly supplied by the CSIRSatellite Application Centre)

The launch of a Soyuzrocket into space.

A NASA satellite caughtthis image of fires in theWestern Cape Province.

20

SPACE EXPLORATION FACT FILEH Rocket-propelled spacecraft were first seriously

studied by a Russian, Konstantin Tsiolkovsky(1857 - 1935).

H Herman Oberth (1894 - 1989) experimentedin Germany with small solid-fuel rockets.

H The first rocket to use liquid fuel was built in1926 by the American, Robert H. Goddard.

H 4 October 1957: the Soviet Union (Russia)began the age of space exploration with thelaunch of Sputnik 1, the first artificial satellite.Sputnik orbited the Earth in 90 minutes andstayed in space for six months.

H Sputnik 2 (USSR, 1957) launched the firstliving creature into space – a dog calledLaika, who spent a week in orbit.

H Explorer 1 (USA, 1958) was the USA's firstsuccessful satellite.

H Telstar 1 was the first communications satellite.Launched in 1962, it carried one televisionchannel. Live television images could be sentto Europe from the USA for the first time.

H 12 April 1961: Yuri Gagarin (USSR) becamethe first man in space.

H 5 May 1961: Alan Shepard becomes the firstAmerican to travel in space.

H Mariner 2 (USA) was the first successfulprobe to visit a planet. It flew past Venus on14 December 1962 and made temperaturemeasurements.

H 16 June 1963: Valentina Tereshkova (USSR)became the first women in space.

H 8 March 1965: The first spacewalk takesplace (Alexei Leonov, USSR).

H In 1966, Luna 9 (USSR) becomes the firstspacecraft to make a soft landing on theMoon and return pictures of the Moon's sur-face.

H The first manned flight around the Moon takesplace in December 1968 (Apollo 8, USA).

H 20 July, 1969: The first Moon landing takesplace (Apollo 11, USA).

H The Russian Salyut 1 became the first spacestation when it was put in orbit in 1971.

H 20 July 1976: The US probe, Viking 1,becomes the first to land successfully on Mars.

H First successful flybys of Jupiter and Saturn bythe space probes Pioneer 10 and 11 in1973 and 1979.

H In 1977 space probes called Voyager Iand Voyager II were launched. Their missionswere to reach Jupiter, Saturn, Uranus andNeptune and send pictures back to Earth.By now (2010) Voyager I has travelled170 billion km and shows signs of nearingthe edges of the Solar System.

H 12 April 1981: The first launch of thereusable spacecraft, Space Shuttle (Columbia,USA).

H 24 April 1990: The Hubble Space Telescopeis launched on board the space shuttleDiscovery.

H 2 November 2000: The first crew to stayaboard the International Space Station arrives.

H July-Sep 1997: Mars Pathfinder, the first Marsrover, explores the surface of Mars.

H 12 February 2001: Spacecraft NEAR softlands on asteroid Eros after studying it fromorbit.

H January 2004: Two Mars rovers, Spirit andOpportunity, land on Mars. Both are stillworking in 2010.

H 1 July 2004: Spacecraft Cassini entersorbit around Saturn to study the planet, itsrings and moons, after a six year journeyfrom Earth.

H 14 January 2005: Cassini's probe Huygenssoft lands on Titan - the first landing on themoon of another planet.

H New Horizons mission launch on 16 January2006; its aim is to reach and study Plutoand its companion Charon. It is expectedthe space probe will reach its destinationin 2015.

21

SOUTH AFRICA ANDSPACE EXPLORATIONFrom the late 1950s to the 1970s South Africaoperated spacecraft tracking stations for NASA.Deep Space Station 51 at Hartebeesthoek laterbecame the Hartebeesthoek Radio AstronomyObservatory, while the STADAN site nearbybecame the CSIR's Satellite Application Centre.

Two South Africans have been into space.IT millionaire Mark Shuttleworth from Cape Townspent a week as a “space tourist” in theInternational Space Station (ISS). He was launchedinto space in a Russian Soyuz three-person spacecapsule from the Baikonur cosmodrome on 25 April2002. Launching people into space is veryexpensive, so it was always government funded.However, modern technology has brought downcosts, and private companies are now developingmanned space travel. The first privately built space-ship was Spaceship One, designed by Burt Rutan.The pilot who first took it all the way into space –higher than 100km above the ground – on a testflight on 21 June 2004 was Mike Melvill, whocomes from Durban. SpaceShipOne can now beseen in the National Air and Space Museum inWashington D.C.

South Africa has also built two space satellites.The first, called Sunsat, was built by StellenboschUniversity. It was launched on an Americanrocket in 1999. It operated for about a year.The second, called SumbandilaSat, was launchedon 17 September 2009 on a Russian rocket. Itwas built by Sun Space and Information Systems inStellenbosch. Sumbandila, meaning “lead theway” in the Venda language, will carry powerfulcameras onboard, able to distinguish objects assmall as 6.25 m from its 500 km orbit above theEarth.

South Africa has now formed its own SpaceAgency to promote the peaceful uses of space.Would YOU like to go into space?

Mike Melvill on Space Ship One.

Mark Shuttleworth in space.

The Fregat Upper Stage of the Soyuz Rocketwith all payloads fully integrated onto it.The huge orange coated satellite is theMeteor M-1 and SumbandilaSat is thetiny black square on the left.

22

FAMOUS ASTRONOMERSAnaximander (611-547 B.C., Ionian) was aGreek philosopher who made the first detailedmaps of the Earth and the sky. He knew that theEarth was round, and believed that it was free-float-ing and unsupported. He measured its circumfer-ence, and was the first to put forward the idea thatcelestial bodies make full circles in their orbits.

Aristotle (384-322 B.C., Greek), the greatphilosopher, proved that the Earth is spherical, andbelieved that it was at the centre of the Universe.

Aristarchus (310-230 B.C., Greek) was the first tobelieve that the Sun was in the centre of theUniverse.

Hipparchus (190-120 B.C., Greek) is consideredthe greatest ancient astronomer. He compiled thefirst star catalogue and also came up with a scaleto define the brightness of stars. A version of thisscale is still used today. He discovered the preces-sion, or slow rotation, of the direction of the Earth'saxis, which is caused by the gravitational pull of theSun and Moon.

al-Khwarizmi (780-850, Islamic) was the inventorof algebra. He performed detailed calculations ofthe positions of the Sun, Moon, and planets, anddid a number of eclipse calculations.

Nicolaus Copernicus (1473-1543, Polish) begana new era of astronomy when he concluded that theSun was the centre of the solar system instead of theEarth.

Galileo Galilei (1564-1642, Italian) is the fatherof observational astronomy. In 1609, he heardabout the Dutch invention of the telescope, and builtone for himself. He saw the craters, mountains, andvalleys of the Moon, noticed the huge number ofstars making up the Milky Way, kept preciserecords of sunspot activity and the phases of Venus,and discovered four moons orbiting Jupiter.

Johannes Kepler (1571-1630, German) used theidea of elliptical orbits to describe the motions of theplanets.

Giovanni Cassini (1625-1712, Italian) was theastronomer who first discovered the division in therings of Saturn. He also found four moons orbitingSaturn, and measured the periods of rotation ofMars and Jupiter.

Isaac Newton (1643-1727, British) was amathematician who described the astronomicalmodels of Copernicus and Kepler. Newtonshowed that the laws governing astronomicalbodies were the same laws governing motion onthe surface of the Earth. Newton's scientificideas still offer an accurate description of physicstoday, except for certain cases in which Einstein'sRelativity Theory must be used.

Edmond Halley (1656-1742, British) becamefamous for predicting the 1682 appearance of acomet now named after him.

Arthur Eddington (1882-1944, British) lead anexpedition in 1919 during a solar eclipse toprove Einstein's theory of general relativity wascorrect. He made the first direct measurements ofstellar masses and discovered the link between themass of a star and its energy output. He alsocorrectly suggested that nuclear fusion was theprimary source of energy in stars.

Edwin Hubble (1889-1953, American) discoveredthat faraway galaxies are moving away from us.This concept is a cornerstone of the Big Bangmodel of the universe.

Albert Einstein (1879-1955, German) wasprobably the greatest mind of the twentiethcentury. His Special Theory of Relativity wasproposed in 1905. In 1915, Einstein extendedthis further in the General Theory of Relativity,which includes the effects of gravitation.

Stephen Hawking (1942-, British) is anotherbrilliant mind of the twentieth century. Hecombined the theory of general relativity andquantum theory in order to prove that black holesemit radiation and eventually evaporate.

23

FAMOUS WOMENASTRONOMERSJocelyn Bell-Burnell (1943 –, British) discoveredpulsars in 1967 as a PhD student at CambridgeUniversity, while supervised by AntonyHewish (who received the Nobel Prize for thediscovery).Annie Jump Cannon (1863 – 1941, USA) wasthe first astronomer to classify the heavenssystematically. She worked as an astronomerand published information about 225 000 stars.Cecilia Payne-Gaposchkin (1900 – 1979, British).Her PhD dissertation, showing stars are madeprimarily of hydrogen and helium, was said tobe one of the best in 20th century astronomy. Henrietta Swan Leavitt (1868 – 1921, USA)discovered that a particular type of variablestar known as a Cepheid could be used asa distance marker, making it possible todetermine astronomical distances to objectssuch as far away galaxies.Carolyn Shoemaker (1929 – , USA) haddiscovered 32 comets by 2002, more than anyliving astronomer. She has also discoveredmore than 300 asteroids.

Women Astronomersin South AfricaWomen play a big role in astronomy inSouth Africa. Dr Patricia Whitelock of theSouth African Astronomical Observatoryuses the variable Mira stars to establishdistances. Dr Sharmila Goedhart of SouthAfrica's KAT/SKA project is an expert on theformation of high-mass stars. Dr ClaireFlanagan at the Johannesburg Planetariumstudies neutron stars. Dr Catherine Cress atthe University of the Western Cape is acosmologist. Professor Renee Kraan-Kortewegheads the Astronomy Department at UCT andstudies galaxies.

SOUTH AFRICANASTRONOMERS in HistorySouth African astronomers have doneexceptional work:H Sir John Herschel was not only an

excellent observer but also a pioneerof photography as well as one of thefathers of education in South Africa.

H Thomas Maclear's geodetic work ledto the establishment of theGovernment Trigonometrical SurveyOffice of South Africa, theMeteorological Commission and theCommission of Standards for Weightsand Measurements.

H David Gill pioneered astronomicalphotography, designed the reversibletransit circle.

H Robert Innes showed that ProximaCentauri was the nearest star to theSun. He was a brilliant self-taughtmathematician and astronomer wholeft school at age 12 and became aFellow of the Royal AstronomicalSociety when he was only 17.

H Dr Bernie Fanaroff studied radiogalaxies and has classes of galaxiesnamed after him. He now leads theKaroo Array Telescope project.

H Dr Thebe Medupe grew up nearMafikeng. He earned his MSc (cumlaude) in Astrophysics, and thenobtained his Astrophysics Doctorateat the University of Cape Town. Hefounded and leads the University ofNorth West's theoretical astrophysicsprogramme, and became a steeringcommittee member of the NationalAstrophysics Space ScienceProgramme in 2002.

These astronomers are just a smallselection of the people who have enrichedour astronomical heritage.

2524

ASTRONOMY IN SOUTHAFRICAHistorySouth Africa has a rich heritage of ethno-astronomy and starlore within several of itsmany cultural groups.

Modern astronomy in South Africabegins with ships. Accurate positions forsouthern stars were simply not available tonavigators, and the position of the Africancoastline wasn't very well known either. In1685 a Frenchman, Father Guy Tachard,set up a small temporary observatoryin the Cape. He and his assistantsdiscovered that most of the stars shown ontheir charts of the extreme southern sky didnot exist at the marked positions, whilemany others were omitted altogether.He also estimated (from observationsof Jupiter's moons) that Cape Town wasnearly 300 km west of its position on hismaps of the Earth.

The first really important astronomer inSouth Africa was Nicholas de la Caille,who spent two years (1751-53) in theCape. He charted the positions of almost10 000 stars and measured the shape ofthe Earth.

In 1820, a permanent observatory wasestablished outside Cape Town. It washeaded by a brilliant young Cambridgemathematician, astronomer and clergy-man, the Reverend Fearon Fallows. Twoobservers were often necessary to getresults with the instruments of Fallows' day,but Fallows had great difficulty gettingeven one reliable assistant. As a result heoften observed with his wife, Mary Ann.Her independent discovery of a comet in1830 places her first on the roll of SouthAfrican women observers in this field.

The history of the South African astronomyalso has roots in other parts of the country.The Natal Observatory was founded inDurban at the time of the 1882 transit ofVenus. The observatory was closed in 1911.

In 1903 the Transvaal MeteorologicalDepartment, from which the RepublicObservatory in Johannesburg later devel-oped, was created.

The present South African AstronomicalObservatory (SAAO) was formed in 1972by combining the Royal Observatory (CapeTown) with the Republic Observatory(Johannesburg). Its headquarters are in theold Royal Observatory buildings in CapeTown. The three most modern telescopes fromthe two observatories found a new home inthe Karoo just outside the town of Sutherland.In 1974 the Radcliffe Observatory telescopeat Pretoria was also moved to the Karoo. TheSouthern African Large Telescope (SALT – seepage 25) is the latest addition to thetelescopes at Sutherland.

Modern Times Since 1972, the SAAO has had the advan-tage of the dark, unpolluted skies of theKaroo, with no special 'cloudy season' whenobserving would be difficult. Research hasconcentrated on understanding the nature andlife cycle of stars of various kinds. Galaxies,both the nearby Magellanic Clouds and themore distant galaxies are observed fromSutherland.

SAAO research has also contributed tounderstanding the centre of our own galaxy,using infrared cameras and detectors to piercethe thick dust clouds that hide the centre fromview. A particular field of interest is the studyof stars whose size and light vary.

In 1961 South Africa became a Republicand as a result of the policy of apartheid,sanctions were imposed. Most of the foreigninstitutions withdrew their support. SouthAfrican institutions were financially hard-pressed to keep the observatories running. In1994 South Africa held its landmark demo-cratic elections and sanctions were withdrawn.The international astronomical communitystarted to re-invest in South Africa's cleardark skies. The southern African region hasbecome a premier destination for cutting-edgeastronomy projects.

Boyden Observatory in Bloemfonteinbecame operational again after a period ofdormancy.

The most exciting post-sanction infusion intoSouthern African astronomy is the SouthernAfrican Large Telescope (SALT) project atSutherland, which was opened in November2005. South Africa's neighbours are alsobenefiting. In Namibia, the H.E.S.S. GammaRay Telescope is in operation. The H.E.S.S.team includes astronomers from North-WestUniversity in South Africa.

SALT

HESS

The 0.5-m Telescope at the SAAOnear Sutherland with the 0.75-m

Telescope in the background. Photo: Helga Nordhoff

26

Radio AstronomyIn the late 1950s, tracking stations for man-made satellites were erected in South Africa. TheHartebeesthoek Radio Astronomy Observatory(HartRAO) near Krugersdorp had its origins incollaboration with the US Jet PropulsionLaboratory, and later NASA. The telescope wasoriginally part of NASA's deep space network oftelescopes responsible for supporting a number ofearly interplanetary and lunar missions. Recentlythere has been increasing interest in radioastronomy. HartRAO has the only radiotelescope in Africa and is much in demand forinternational collaboration. HartRAO is assistingin the development of a new radio telescope inNigeria.

HartRAO

HartRAO

27

The Square Kilometre ArrayRadio TelescopeSouth Africa is currently bidding to host thelargest ever radio telescope to be built byan international group of collaborators, theSquare Kilometre Array (SKA). This radio tel-escope will be able to probe the secrets ofthe time the Universe was formed. Australiais the other country remaining in the compe-tition to host the SKA.

To help develop the new technologiesneeded for the SKA, South Africa is building

demonstrator telescopes. The first of these iscalled the eXperimental DevelopmentModel (XDM). It is 15 metres in diameterand was built at Hartebeesthoek in 2007.Currently under construction is the KarooArray Telescope – 7 (KAT-7). This is a groupof seven telescopes each 12 metres indiameter being built west of Carnarvon inthe Northern Cape. It is expected that thiswill be followed by an array of dozens ofsimilarly sized telescopes, called MeerKAT.

Above: MeerKAT Prototype

Completed MeerKAT dishes

An artist’s impression of the completed SKA

28

Space Geodesy“Geodesy” means the measurement of theshape of the Earth. Space Geodesy inSouth Africa is a spinoff of radio astronomyat Hartebeesthoek. It started as part of aNASA programme to measure the present-day movement of the continents. TheHartebeesthoek 26 metre diameter radiotelescope took part in this programme,starting in 1986. The telescope, which isattached to bedrock, was found to bemoving North-East at 25mm per year. This1992 result was the first measurement of themotion of the African continent, and hasbeen confirmed by many years of measure-ments since then.

The radio telescope is the most accuratelylocated point on the African continent. As aresult, from 1998 its position has been usedas the reference point for the survey systemof South Africa, used for accurate positionmeasurement. This replaced the old systemwhich dated back to the 1880s, and inwhich the astronomers at the CapeObservatory (now SAAO) had beeninvolved.

The Space Geodesy Programme in SouthAfrica now also operates a NASA SatelliteLaser Ranger (SLR). This uses a laser whichfires high power pulses of light at satellites.Mirrors on the satellites reflect the light backto the SLR, which measures how long theround trip took. As the speed of light isknown, the distance to the satellite is easy tocalculate. This system can measure theorbits of satellites to an accuracy of a fewcentimetres.

In addition, Global Positioning System(GPS) receivers have been set up in severalplaces in South Africa and in other SouthernAfrican countries, on Mauritius and Marion

Island in the Indian Ocean and at theSouth African National AntarcticExpedition (SANAE) base in Antarctica,in order to measure their movements.Several are placed alongside tidegauges so that together they canaccurately measure the change in sealevel caused by global warming. GPSreceivers work by comparing the signalsreceived from a number of satellites inorbit overhead to calculate the positionof the GPS receiver on the land.

Right:GPS Satellitein Orbit

Above:NASASatelliteLaser Ranger(SLR)

Above: GPS Antenna

Below: SLR Operator