THE MOON Writtenby FELIXSUTTON Illustratedby RAULMINAMORA EditorialProduction: DONALDD.WOLF Editedunderthesupervisionof Dr.PaulE.Blackwood, Washington,D.C. Textandillustrationsapprovedby OakesA.White, j/BrooklynChildren'sMuseum, Brooklyn,N. Y. Introduction Themoonhasbeenthesubjectofspeculationandimaginativeques-tioning by mankind throughthe ages.A closeneighbor inspace,itsrhythmic sequencesofcolorandformarevisibleeventotheleastobserving.Yetat timeseveryoneobservesthemoon.Suchagloriousneighborinspacemust have a special significance! The wonder of it has raised hundreds of questions. Andnowtheanswersmaybeours.Foratlonglastmanisonthethreshold of going to the moon. ThisHowandWhyWonderBookoftheMoonpreparesthereaderto understandthemoonexplorations.Notonlydoesitsummarizemuchthat isalreadyknown,italsostates clearly someof themajorquestionsyettobe answered.Inmany ways our attempt to reach the moon illustrates science and technologyworkinghand-in-handinspectacularways.At firstitseemsthat onlyouterspaceisthelaboratoryinthisexploration.Butcloserthought remindsusthattheresultsof researchofmanykinds - fromtesttubesto mathematicstotelescopicprobingofthevastuniverse - havecontributed tothesoon-to-beaccomplishedflightstothemoon. Livinginthetwentiethcenturyisexciting.Thinkoftheopportunities thatchildrenatschoolandwholefamiliesathomehavetolearnaboutnew scientificadvances.ThisHowandWhyWonderBookoftheMoontakes ustothefrontiersofknowledgeaboutourEarth'smajorsatellite.Surely moon-gazing,alwaysapopularactivity,willneverbethesameagain.And inadaywhenthequestionisnot"Shallwelookatthemoon?"but"Shall wetakeatriptothemoon?",thegreatyellowsphereemerginginfull splendor over the eastern horizonhas a new meaning for everyone. PaulE.Blackwood Dr.BlackwoodisaprofessionalemployeeintheU.S.OfficeofEducation. Thisbookwaseditedbyhiminhis . privatecapacityandn.oofficialsupportor endorsementbytheOfficeofEducationisintendedorshouldbeinferred. LibraryofCongressCatalogCardNumber :67-24099 1967byGrosset&Dunlap,Inc. 1963byWonderBooks,aDivisionofGrosset&Dunlap,Inc. AllrightsreservedunderInternationalandPan-AmericanCopyrightConventions. PublishedsimultaneouslyinCanada.PrintedintheUnitedStatesofAmerica. TwelfthPrinting Contents OURNEIGHBORINSPACE -. THEMOON4 Whatistheoriginofthemoon?4 Mythsaboutthemoon6 What istheharvestmoon?thehunter's moon?7 What wasthe "Great Moon Hoax"?7 Howlargeisthemoon?9 Howfarawayisthemoon?10 What are dayand night onthemoon?10 Why does the moon shine?11 What color isthe moon?12 How does the moon cause tides?12 Why does the moon stay in orbit?13 Willthemoonalwaysstayin orbit?14 Whatisaneclipse?15 Howdidan eclipse save Columbus?16 In what yearwasJesusborn?16 Whatcausesan eclipse?16 Whatisaneclipse ofthesun?17 WhowasGalileo?18 Whydo wesee onlyone side of the moon?19 How can we see the moon's "far side"?20 Whatisthemoon-scapelike?21 What are the mountains on the moon?22 What are the craters?22 What are rills?24 Whatarethe"rays"?24 What are the "seas"?25 What do weknow about the moon's surface? 26 Do air and water exist on the moon?28 Doeslifeexistonthemoon?28 Arethereanyothermoonsinoursolar system?29 Doesthe moon contain valuable minerals?30 Why do we want to explore the moon?31 Howwillmen get tothemoon?34 What are the Rangers?35 What isthe balsa ball?3 7 What willthe ball tell us?38 What isthe Surveyor?39 What isProject Apollo?40 Whatisthe Gemini?42 What isthe "bug"?42 Why willApollo firstorbit themoon?43 How will men work in space?43 Howwillthefirstmoonlandingsbemade?46 Howwillthemoonexplorersgetaround?46 Howwillmansurviveonthemoon?4 7 Youandthemoon48 Preface Fromthebeginning ofhistory, manJ!ip been Obsessed. by the desire to tnt'Ve1to th mooa.Aseal,carvedin 3,000' yearsago,showsaman mountedonthe bt\ck of a great bird obviouslyheaded fot a till}'ctescent modnthatshowsin a cC>tfier of fNt ls lie story of the approach1ng real-izationofthisago.olddream.Project Apollo isthe plan which willone day place a inanfromearthonthedesolationofthe moon. What wenow knowabout the moon and what morewemust learnaboutit be-fore we can risk human lives on this exploit are toldhere.Herealsoisthestoryof the carefullydetailedpreliminaryresearch -themannedandunmannedexplorations that must precede the actual event. .This may be man's greatest adventure. It willbe one upon which he will embark with his eyes open, not blindly or desperately,as hehasonmanypastexplorations.The storyofProjectApolloisasexcitingas ml.1sthavebeenthepreliminariesforthe voyagesof Columbus,about1490. James S.Pickering HaydenPlanetarium One theory contends that the moonisa portion of the earth that was thrown-off whiletheearthwasstillsemi-liquid. According to another theory, the moon 'wasformed fromachunk of earthtorn fromwhatisnowthePacificOcean. OurNeighborinSpace - theMoon For the firsttime in allhistory,man is reaching out to probe the mysteries of space.Scientistshavealreadysentour astronautsmorethan, 150mileshigh, hurtlinginorbitaroundtheearthat speedsofover17 ,000milesperhour. Before youare mucholder,thefirst humanexplorerswillsetfootonthe moon.Fromthere,thenextstepping stoneintheconquestofspacewillbe Mars,andafterthat theother planets. Then, at some unforeseeable date in the future, man plans to go on to the distant starsthemselves. Sincethemoonistheclosestofall theheavenlybodies,itwillbethefirst 4 to be probed by men from earth. In this book, we will seek some answers to ques-tions about what the moon is like; what ourastronautsarelikelytofindwhen they get there;and howthey willmake the long and hazardous voyage through theempty reachesof space. There have been a great many scientific theoriesabouttheori-Whatistheginofthemoon.Of originof themoon?these,onlythethree most likely 'Yillbe dis-cussedhere.Thefirstholdsthatthe moonisathrown-offportionofthe earthitself.Whentheearthwasnew and in a semi-liquid form, its rapid revo-lutionaroundthesuncausedittoas-sume the shape of alop-sided dumbbell The smaller part of the dumbbell broke . away and became the moon. A corollary to this theory is that after the earth had begun tosolidify,ahuge chunk of it was torn loose from what is Most scientiststoday accept thetheorythatoursolar systemwasformedfromacosmiccloud. Thesunforms. nowthebasinofthePacificOcean. Abouttheonlyjustificationforthis lattertheory,mostscientiststhink,is the fact that the total mass of the moon wouldjustaboutfilltheholethatis now filledby the Pacific's waters. Otherscientistsbelievethatthe moonisactuallyolderthantheearth. They contend that the moon is a relic of an earlier stage of the solar system than that during which the earth was formed. Towardtheendoftheearth'sforma-Theplanetsandmoonsformwithinthedustrings. ,, . Moons are capturedby theplanets'gravitational pull. 5 0 0 tion,it caught the moon inthe forceof itsgravity and capturedthe moonasa permanentsatellite. Mostscientiststoday,however,ac-ceptthetheorythat themoonandthe earthwereformedatthesametime andofthesamebasicmaterials.They thinkthat severalbillionyearsagoour solarsystemwasnothingbutacloud of cold dust particles whirling aimlessly throughthenothingnessofdeepspace. Then, in response to the laws of gravity, these particlesgraduallycametogether toformahuge,spinningdisk.Asit spun, the disk separated into rings.The nucleus of the disk became the sun, and theparticlesintheouterringsbecame the planets. When both earth and moon hadbeenformed,themoon,being muchthesmaller,wascaptured bythe stronger gravity of the earth and sobe-gantoorbitaboutitjustastheearth orbits around the sun.(See ill. p.5.) Becausethemoonisthenearestheav-enlybody tothe earth, Mythsabout. and because 1tappears at different times of the .themoon month inseveralvariedforms,agreat manymythsandsuperstitionshave grown up about it. Here are a fewof the mostcommon. Manypeoplebelievethatthemoon affectstheweather.Whenthemoon changes,they say,the weather changes. As a result weget old-time sayingsthat havebeenhandeddownfromgenera-tionto generation: "Clear moon,frostsoon." "Pale moonmeansrain.Dark moon means winds." "Whenthe mooncanbeseeninthe daytime,the daysarecool." 6 "Frost inthedarkofthemoonkills budsandblossoms;frostinthelight ofthe moondoesnot." Anyonewhostopstothinkaboutit soon realizes that the moon cannot pos-sibly change the weather on earth. First, itisaninertbody,aquartermillion milesaway,whichtransmitsnoenergy exceptaweakreflectionofthesun.In the second place,the moon can be seen over half the earth at the sametime,in thetropicsaswellasthearctic,and obviously every place on earth doesnot have the same weather. Many old-timers also believe that the moonaffectsthegrowthofseedsand plants. "Plant beans when the moon is light." "Plantpotatoeswhenthemoonis dark." "Wood keepsbetterwhencut in-the newmoon." "Trees should onlybe pruned in the new moon." For centuriesfarmershaveplanted and tilled their crops in accordance with these ancient rules.But no one has ever beenabletoprovethatthemoonhas anythingatall _ todowithearthly harvests. .. Sincelongbeforethefirsthistory books were written, people believed that thefullmooncausedinsanity.In fact, the word "lunacy" comes from the Latin word "luna" meaningmoon.It wasbe-lievedthat ifthe fullmoonshoneona person while he were sleeping,that per-sonwouldgomad.Anotheroldsuper-stitionsaidthat moonlightcouldcause blindness.But sincemoonlightisnoth-ingmorethan reflectedsunlight,the sunshouldcauseagreatdealmore madnessandblindnessthanthemoon. The moonhasalwaysfiguredprom-inentlyin both ancientandmodernre-ligion.It wasworshippedasagoddess bytheGreeksandRomans,aswellas native tribes in Asia,Africa,Australia, andNorthand SouthAmerica. Today,thephasesofthemoonplay an important part inthecelebrationof bothChristianandJewishHolyDays. The Christian festivalof Easter always takes place on the first Sunday after the first full moon after the vernal equinox. Oneofthemostsacredofalldaysin theJewish faith,Passover,alwaysfalls on the first full moon of the spring, from the14th tothe 21st dayoftheHebrew monthNizan. The fullmoon whichisnearestindate Whatisthe harvestmoon? thehunter'smoon? totheautumnal equinox(Sep-tember23)is knownasthe "harvest moon." At this time,the moon rises early in the evening for three nights RichardAdamsLocke's "Great Moon Hoax" of 1834. "'-,_ ; insuccession,andisentirely ornearly full on each of the nights. Thus the light ofthemoonlengthensthenatural periodoftwilight,andallowsfarmers extrahoursofworkingtimeinwhich toharvesttheircropsbeforethefall frostssetin. The "hunter's moon" followsthe har-vest moon,one month later,and isvery similar toit.It issocalledbecausethe hunting seasoi:i followsthe gathering in of the crops. Therehavebeenmanyfantastictales Whatwas the"Great told about the moon. Butperhapsthe mostridiculouswas MoonHoax"? the"greatmoon hoax"of1834.The amazingthingwas thatmostofthepeopleoftheworld, includingagreatmanyleadingscien-tists,were completely taken in by it. It allbeganoneafternoonwhena reporter for the NewYork Sun, Richard Adams Locke,wastryingto thinkofa 7 + + sensational story to write forhispaper. It had been a dull day for news. Nothing ofmuchimportancewashappeningin thecity.SoLockelethisimagination take over. He knewthat SirJohn Herschel,the famous British astronomer, was making moonobservationsatthattimefrom the Cape of Good Hope in Africa. That wasenoughofastart fortheimagina-tiveMr.Locke.Hisstorytookit from there. He reported that Sir John had devel-oped atelescopetwenty-four feetindi-ameter,which wasbigenoughtobring the moon into view at a relative distance of150yards.Throughit,theastrono-mercouldseeflowers,whitebeaches, If you wonder about the relation of size betweenmoonandsun,youmight understandit bette.rif yourealizethat thesunismuchlargerthantheearth-moonsystemtogether . Themoonis"only" 6; BUOmilesincir-cumferenceand2, 160milesindiam-eter.Thismeansthatalinedrawn throughitsaxiswouldextend"only" fromNew YorktoSalt LakeCiJy. andahugejewel-likerock,probablya ruby,that was90feethigh.In avalley nearby,sowent Locke's fancifulstory, were herds of small bison and blue uni-corns,aswellasflocksofpelicansand other birds. Asthe dayswent past,LDcke'snews storiesgrewevenmorefantastic.He reportedthefindingoftwo-legged beavers,hornedbears,andhuman-like creaturesthatwerehalf-manandhalf-bat. Afterafewweeksofwritingthis fabuloushoax,Lockedecidedtoquit. But by this time,the circulation of The Sun, which had been a small, unsuccess-ful paper, had ballooned into the largest inthe. city.Lockehimselfbecamefa-mous,evenafter he had confessedthat hisstorieswereonlywildfigmentsof hisimagination. Since the moon'sgravitational pullisonly1/ 6of theearth's, itwouldbeeasytobreak earthlyleapingandweight-liftingrecordsonthemoon. Themoonswingsaroundthe earthinanellipticalorbit whichis252,710milesaway .fromtheearthatitsfarthest point,and221,463milesat Themoonis2, 160milesinHowlarge isthemoon? roughlyone-quarter thediameterofthe earth.Inrelationto thewidthoftheUnitedStates,this meansthatalinedrawnthroughthe axisofthemoonwouldextendfrom New York to Salt Lake City,Utah. The moon's mass (roughly its weight) is1/ 8 lst that of earth's. Since the gravi-tationalattractionofabodydepends uponitsmass,scientistshavedeter-minedthatthepullofgravityonthe moon'ssurface isjustone-sixthofthat onearth.Thismeansthatifyounor-mallyweigh150pounds,yourweight on the moon would be only 25pounds. If youcanjumpthreefeetintotheair on earth, you could jump18feet on the 9 moon.To useanotherexample,ifyou can lift100 pounds on earth, you could lift600poundsonthemoon.Thus, when the first explorers reach the moon, they will have little difficulty in moving andliftingheavypiecesofmachinery and equipment that they could not even budge on earth. The moon swingsaround the earth in a slightlyellipticalor-Howfar away isthemoon?bit. At its apogee, its farthestpointfrom earth,themoon is252,710milesfrom us.At itsperigee,or closest point,it is 221,463milesaway.Theaveragedis-tancefromtheearthtothemoonis 238,857miles.Aspaceship,launched from earth, would take roughly two and a half days toreachits destination. Light fromthemoonreachestheearthin aboutoneandone-quarterseconds. Radioandtelevisionsignalstravelat the same speed as light. This means that an explorer on the moon would be able toconversefreely,viaradio,withhis earthbase. The earth rotates on itsaxisonce every Whatareday andnighton themoon? 24hours.Thus,its averagedayand night are each of12 hoursduration.The moon orbits around the earth once every 27113days,andinthissameperiodit turnsonlyonceonitsaxis.Thus,the lunar"day"isequaltoabout14earth days,andthelunar"night"isofthe sameduration. Ofcourse,onesideofthemoonis alwaysilluminatedbythesun - just asisonesideoftheearth.Thus,when 10 itis"night"inonemoon-hemisphere, it is"day" in the other. Duringthe"day,"whenthesurface of the moon is fully exposed to the sun's rays,thetemperatureofitssurfaceis about220degreesF.Thisisslightly higherthantheboilingpointof water. At"night"onthemoon,thetempera-tureplungestoabout250F.below zero. Butsincethemoonhasnoatmos-pheretoabsorbandtransferheat,the darkshadowcastbyanoverhanging rockisascoldduringthe"day"asit would be at "night." Thus,if youwere standingonthemoonwithyourright footinthefullsunlight,andyourleft footindeepshadow,thenyourright footwouldbeexposedto220degree heatandyourleftfootto250-below-zerocold.It iseasy toseethat the first moonexplorersarenotgoingtohave a very comfortable time. Theair onearth,whenexposedtothesun,evensout thetemperaturebetweensunnyandshadedplaces. Butthelackofatmosphereonthemoonmakesthe sunlitspots"boilinghot"andtheshadows"freezing cold," withnothinginbetween. ,, e s s v If youcouldlookatearthandmoonfromapointinspace,themoonwouldalwaysappearhalfdark.The fact that weseethevariousphases(innerellipse)iscausedby the changingangle under whichwe seethe sunlit surface of the moon fromour observationpoint onearth. Liketheearth,themooncreatesno lightofitsown.The Whydoesthe moonshine?moonlightweseeon a clear night isonly a reflectionofthesunlight.Forthisrea-son, the moon seems to assume different shapesatdifferenttimesofthelunar month asit orbitstheearth.These are called the phases of the moon. When,initsjourneyaroundthe earth, the moon comes into a direct line withthesun,wecannotseeitatall. This iscalled the "new" moon.Twenty-fourhourslater,asmallpartofitre-flectsthesunlightasathincrescent. Thisiscommonly knownasa"sickle" moon.Afteraweek,thecrescenten-largestobecomea"quarter"moon. And in another week,the entire ballof themoon,orthe"'full"moon,1sex-posedtoourview.Themoon'sphase thengraduallyrecedesintothethird quarter,intoacrescentagain,andfin-allyintothenewmoontocomplete once more itsmonthly circuit. If youwereanexplorerstandingon the moon and looking at the earth,you wouldseethesameeffects.Theearth would shine in the reflected light of the sun,andyoucouldproperlycallit "earthlight."Atvariousphasesofthe earth's passage overhead, you would see "full" earth"quarter" earthand "cres-'' cent"earth.And,ofcourse,at"new" earth, you could not see it at all. Itisquitelikelythatyouwouldbe abletodistinguishtheearth'svaried colors - thegreenoftheforested areas,the brown of the deserts,and the blue-blackof theseas. 11 Thecolorofthemoon,asweseeit, dependsuponitsre-What colorfld 1.h..fil .th?ecte1gtas1t1s-1semoon. teredthroughthe earth's atmosphere. Thus, in wintertime, whenthe moonrideshigherinthesky HIGHTIDE LOWTIDE Thereisahightideandalowtideabouteverysix hours.Inotherwords,duringapproximatelyevery 24hours,atanypointonthe . shore,therearetwo hightidesandtwolowtides. and its rays shine almost directly down, it appearsto be white or silver.In sum-mer,themoonmovesat alowerangle c ~ o s s theskyanditsraysarefiltered throughthickerlayersofatmosphere. It then appearsto beyellowor golden. If youwerestandingonthesurface of the moon itself,withnoatmosphere to reflect or refract the light, the moon's color wouldprobably bedeepblackin the shadow and gray-white in the direct sunlight. If youhaveeverbeentotheseashore, youmusthave Howdoesthemoon 0 bservedthe causetides? dailyebband 'flow of the tides.At certain time of the day,thelevelofthewaterrisessome-timesasmuch astenor twenty feet.A fewhourslaterthetidehasreceded, leaving behind it a long stretch of empty beach.Thesetidalflowsarecaused mainly~ y thegravitational pullofthe moqn, and to a lesser degree, of the sun. During the periods of newmoon and fullmoon,theearth,thesun,andthe Whenthemoonandthesunline uponthesamesideof the earth,or whenthesunandthemoonare inline,but onoppositesidesof theearth,thecombinedgravitationalpullcreatesunusuallyhighor springtides.Whensun andmoonareat rightangles,thegravitationalpullof eachworksagainsttheotherandunusuallylow or neap tidesresult . 12 a 0 wn, um-1gle red ~ r e .en. :ice ere n's Ill ~ c te, ve Le td te \ I, y :I moonareinastraightline.Thus,the moonandsunworktogethertocause extremely high tides, known as "spring" tides.Whenthe moon isin itsfirstand thirdquarters,itisatrightanglesto the sun in relation to the earth. At these times,themoonandsunarepulling againsteachother,resultinginlower tides,called"neap"tides. Asbillionsoftonsofseawaterare constantlybeingdraggedbackand forthacrosstheoceanfloors,the .fric-tiontheycreateactsasabrakeonthe rate oftheearth'srotation.And asthe earth's rotation slows, the days lengthen. Theresultisthatourdaysaregetting about one second longer every100,000 years. If youattachaweighttoastringand swing it around Whydoesthemoonhdth t .b't?yourea,e saymor1. weighttravels in a circle. This is because two opposing Whenone shore of the oceanhashightide,the other haslowtide.Thefrictionthatiscreatedbythecon-stantdraggingofbillionsof tonsofwaterslowsthe rateof theearth'srotation. LOWTIDE PATHOFMOONWITHOUT Thediagramwillhelpyoutounderstandhowand whythemoonstaysinorbit. forcesareworkingonitatthesame time.Aforcecalledtangentialvelocity tendstothrowtheweightoffina straight line, just as the weight would do if you let go of the string. But the string, held in your hand, keeps pulling it back. Thus the weight moves in a circle. The moon revolves in a circle around theearth inresponsetosimilarforces. MOON Theorbit of themoonbecomesproportionallylarger withtheslowingdown of theearth ' s rotation. Hurtlingalongataspeedof2,287 milesperhour,tangentialvelocity triestoflingthe moonoffinastraight line away from the earth. But the earth's gravityactsinthesamewayasthe string;itkeepspullingthemoonback towardstheearth.Thusthemoon travelsserenelyaroundusinitsorbit. It isthissameprinciplethatallows the spaceships of our astronauts tostay in an earth orbit. The outward thrust of theshipisequalizedbythedownward pulloftheearth'sgravitationalforce, andsothespaceshipkeepsgoing around in acircle.Whentheastronaut wishes to bring his vehicle back to earth, hefiresaretrorocketwhichslowsthe ship's orbital speed and thusupsets this delicate relationship;then the ship falls back into the earth's atmosphere. Wehaveseenthatthefrictionofthe tideshasabraking Willthemooneffectuponthe alwaysstay earth's rotation,and inorbit? thatasaresultour daysare becoming longer,at the rate of about1/ 1,000th of asecond a century. Thisrateofchangeissoinfinitesimal that it seems absurd even to think about it.But,overfutureeons,itwillaffect theultimatedestinyofthemoon,and willeventually(after countlessbillions ofyears)probablybethecauseofthe moon'sbreak-up,disintegration,and death. Thistidalfrictionwasjustaseffec-tive on the earth and on the moon when bothbodieswereinaliquid,orsemi-plastic, stage, as it is today on the waters 14 oftheearth'soceans.Theresultwas thatthemoon'speriodofrotationon itsaxisbecameexactlythesameasits periodofrevolutionaroundtheearth. Now,asthe earth's rotation becomes slower(evenbyonly1/1,000thofa secondin100years),theorbitofthe moonbecomesproportionallylarger. Thus the moon's distance from the earth increases,andthemoon-monthbe-comeslonger. Thesechangesduetotidalfriction have been going on for billions of years, just as they are still going on. The earth-day,which wasoriginally lessthan five hours, has lengthened to 24 hours.And themoon-month,whichwasoriginally thesamelengthastheearth-day,has increasedtoabout fourweeks. Astronomersnowcalculatethatthe slowlengtheningoftheearth-daywill continue until it isaslongas55of our present days,and the moon-monthwill also increase to55of our present days. At that time,the earth willalways keep thesamesidetowardthemoon,asthe as m ts h. a Le r. h "-n s, l-e d s I moonnowkeepsthesamesidetoward the earth. If at that far distant time,the oceansoftheearthstillexist - andif theyarestillinaliquidstate - there will be a constant high tide on the earth under the moon. Therefore there will be nomoretidalfrictionproducedbythe moon.Themoonandtheearthwill goaroundtheircommoncenterof gravity asthough lockedtogether.The lengtheningofour earth-day willcease whenithasbecomeequalto55ofour present days. Whenthisbalancepointhasbeen reached,the earth's rotation willgradu-ally slow down until it is longer than the moon-month.Nowtheearth-moonre-lationshipwillbereversed.The earth's rotationwillagainspeedup,andthat ofthemoonwillbegintoslowdown. Thus,themoonwillgraduallyreturn towardtheearth. Thisprocesswillcontinueuntilthe moon isat last dragged downtowithin suchashortdistanceoftheearththat it will be broken up by the action of the Inmany billionsof yearsthe moonwillbe pulledbacktowardtheearth,anddis-integrateuponenteringtheearth'sat-mosphere.Thenitsparticleswillform ringsmuchliketheringsaroundSaturn. earth'stidalpull.Insteadofcolliding with the earth,the particles of the shat-teredmoonwillcollecttogetherand formaseriesof ringsaroundtheearth much like the rings of the planet Saturn - although the rings will be much more massive. Butalloftheseamazingthingswill not happen until many billions of years inthefuture. Whenthefullmoonmovesintothe deep shadow of the earth Whatisan. I.?and seemstodisappear, ec1pse. wecallittheeclipseof the moon.There are usually one or two suchlunareclipsesthatarevisiblein the United States each year,and almost everybodyhasobservedat leastonein hislifetime.Mostofusenjoywatching thespectacleofthemoonbeingap-parentlyswallowedupbytheearth's shadow. But inancienttimes,peopledidnot knowwhatcausedeclipses,andthey werefrightenedbythem.Eventoday, 15 among some of the more primitive tribes in Africa, an eclipse causes great terror. A story states that on his fourth voyage totheNewWorldin Howdidan1504,ChristopherCo-eclipsesavelumbussavedhimself Columbus? andhiscrewbyhis knowledge that a lunar eclipse was com-ing on a certain night. Columbusbadly neededsuppliesfor hisships,but the Indians refused toget themforhim.HethentoldtheIndian chiefs th.at the Christian God was angry because they had refused their help; that He would punish them with famine; and thatasasignofHisangerHewould remove the moon fromthe sky. When the eclipse began asColumbus ! / I . ' Alunar eclipse occurswhenthemoonpassesthrough theearth'sshadow.Usuallyinalunareclipse,the moonappearsdarkenedtoadeepcopperred. 16 hadsaiditwould,theIndianswere panicstricken.Theypromisedtofur-nishalltheprovisionshewantedifhe couldpersuadehisGodtogivethe moonbacktothem.Whentheeclipse had passed, the Indians complied. Sinceastronomersareabletofigure backwardsandde-Inwhatyeartermine the dates of wasJesusborn? .lunar eclipses in the fardistantpast,theyhavebeenable toestablishaccuratedatesforagreat many historicalevents. An eclipse of the moon took place on the night before the death of the Judean KingHerodwho,duringthefinalyear ofhisreign,orderedthedeathofall malechildreninBethlehem.Hehad hopedthatthebabyJesuswouldbe killed in the general slaughter. We know thatthisparticular eclipseoccurredon March13,intheyear3 B.C.Thuswe canconcludethatJesuswasbornat leastfouryearsbeforethecalendar beginning of the Christian era. Theearthorbitsaroundthesunina levelplane.Forex-Whatcauses ample,ifwesuppose aneclipse? thatthesunisinthe center ofadining-room. table,thenthe earth moves around it on the same level as the table"s top.On the other hand, as the moon goes around the earth its path istilted about fivedegrees.That iswhy wedonothaveaneclipseduringeach full .moon.The earth, of course,always castsashadowwhichextendsnearly 859,000 miles into space,but the moon ordinarilypassesaboveorbelowit. However, when the moon is in the same Whenwillthenexteclipseoccur? Hereisascheduleoflunareclipses whichcanbeobservedintheUnited Statesduring the next ten years. 1963-December30 1964- June25 December19 1965 - June14 1967 - April24 October18 1968 -April13 Octoberfr 1970 - February21 August17 1971- February10 August6 1972 - January30 July26 1973 -December10 plane as the earth during full moon,the earth'sshadowblotsout the moonand an eclipse occurs. An eclipse of the sun takes place during the new moonwhenthe Whatis moonisbetweenthe aneclipseearthandthesun.The ofthesun? shadowcastbythe moon variesinlength from228,000to 236,000miles.Forthisreason,most ofthetimeswhenthemoonisinthe rightpositionforasolareclipse,the moon'sshadowdoesnotreachthe earth. On theother hand,whennewmoon occursduring perigee(whenthemoon isatthelowestpointinitsorbit),the moon'sshadowextendsseveralthou-sandmilesbeyondtheearth.Onsuch occasions, the shadow cast by the moon ontoearth maycoveranareaofsome 475sq.miles. Itisfortheabovereasonsthat eclipsesof the sunare rare and fleeting events. They last for only a few minutes, and take place at many different points over the earth's surface. If, for example, astronomers know that a solar eclipse is scheduledtooccur at Kano,inAfrica, on a certain date,they willspend many many months setting up their equipment at that locationinorder' totakephoto-graphsof thephenomenon. In ancient China and Egypt, the high prieststaughtthepeoplethat whenan eclipsecameanevildragon-spiritwas Asolareclipseoccurswhenthemoonpassesbe-tweentheearthandthesun,blockingviewofthe sunfromasectionof theearth. 17 eatingupthesun,anditwoulddis-appear forever unlessprayers weresaid andofferingsweremade.Otherma-giciansandsorcerers,knowingthatan eclipsewasdue,threatenedtoremove thesunfromtheskyunlesscertain oftheirdemandsweremet.Whenthe eclipsebegan,thepeoplewerecon-vincedthatthemagicianwasmaking goodhisthreat.Aftertheygavehim whathewanted,hewouldpromiseto makethesunreappearinafewhours, whichofcourseitwasgoingtodoin I anycase. If youareeverluckyenoughtosee atotalsolareclipse,youwilldiscover that it isan awe-inspiringsight.Asthe moon approachesthe sun,the skiesbe- . gin todarkenastheydoat normal twi-light.Onthefarms,chickensgoto roost,thinkillg that it is nightfall. When the moon completely obscures the sun's . flamingball, the sky becomes almost as darkasamoonlessnight.Then,ina few minutes, the moon passes across the sunanddisappearsfromview,andthe day becomes bright again. Galileo,thefirstmanto lookatthemoonwith amagnifying telescope. 18 ' Eversincethedawnofhistory,men havebeengazingupat Whowas Galileo?the moon and speculating aboutit.Becausethey could seeit nobetter than wecan with the naked eye,they were not able to tell muchaboutit.Thefirstmanwho viewedafairlygoodclose-upimageof the moon was an Italian scientist named GalileoGalilei.He isknowntohistory by his first name. Asascientist,Galileo wasfarahead of his time.When he was only nineteen, and astudent at the Universityof Pisa, he observed the slow swinging of a lamp suspendedfromthehighceilingofa cathedral.Fromthishedevelopedthe theoryofthependulum,andwasthe firsttoapply it tothe measureoftime. According to legend, by dropping metal ballsof differentsizesfromtheleaning towerofPisa,heprovedthatweight hasno influenceon the velocity offall-ingbodies.Healsodeterminedtheac-celeration of falling bodies. Galileobecame interestedinobserv-ingtheheavenlybodies,butwasfrus-trated because he could not get a clearer look at them. Then,in1609,helearnedthata Dutch spectacle maker named Jan Lip-persheyhadbuiltagadgetthatcon-sistedofseverallensesputtogether ten at ng ey ith ell 110 of ~ ry ld n, a, p a .e e ' ,, tl g t Thetelescopeusedby Galileoadvanced knowledgeaboutthe moonconsiderably.To-day,camerasmounted onpowerfultelescopes inourgreatobserva-toriesareabletotake remarkablyclearpic-turesof thesurfaceof themoon.Thesecamerasare capableofmakingaccuratephotographsof objects onthemoon-scapethatareonlyaboutahalf-a-mile inlength.Forthisreason,nomajormoon-mark(as compared to landmark) hasgone undetected. insideatube.Itmadedistantobjects suchastreesorpeopleappeartobe quiteclose.Lippersheycalleditthe "magictube."Galileoquicklyjumped at this novel idea.He refined the lenses, adjustedtheirpositioninginsidethe tube,andsobuiltatelescope. Wecan imaginehowexcitedhewas when he first turned his telescope on the moon.Forthefirsttime,hesawits craters,itsmountainranges,andits huge expanses of broad flat plains. Since these latter areas appeared smooth and featureless,aswouldlargebodiesof water,he called them seas. For therestofhisbusylife,Galileo spentagoodpartofhistimestudying theheavens.Hegreatlyexpandedhis observations of the moon.He observed thedarkspotsonthesunthroughhis telescope. He discovered the crescent of VenusandthefourmoonsofJupiter, and concludedthat thehazyfogofthe MilkyWayactuallyconsistedofmil-lionsofseparatestars . . Ofcourse,Galileo'sfirsttelescope wasacrude and primitiveaffair,but it wasthegreatgrandfatherofthehuge telescopesthattellussomuchabout themoon'ssurfacetoday. Theearthrotatesonitsaxisinawest Whydowesee onlyoneside ofthemoon? toeastdirection onceevery24 hours,thuscaus-ing night and day. The moon rotates on its axisand in.the same direction_to produce night and day on the moon.But there isone great differencebetweenthetwobodies.The moon rotates on its axis only once every. 271/3days,or,once during each time it orbits the earth. Thus,thespeedoftheearth'srota-tion is about 1,000 miles per hour at the equatorwhilethemoon'srotation speed at itsequator isonly10.35miles per hour. These tworotation speeds are sodelicately adjusted that the same half ofthemoonisalwaysturnedtowards theearth.Wecallthisthe"earthside" ofthemoon.Thehalfthatwenever seeiscalledthe"far side." Youcanmakeasimpleexperiment 19 thatexplainswhywealwaysseethe same sideofthemoon.Placesomeob-ject,suchasachair,inthecenterof aroom,andassumeforthemoment that it isthe earth and you are the moon. Nowwalkslowlyaroundthechairin acounter-clockwisedirection.When you have made one complete circle, you willobserve that yourbody hasrotated once in relation to the walls of the room. But onlythe leftsideof yourbodyhas been turned toward the chair.The right sideofyourbodyhasalwaysbeen_ hidden from it. If themoonorbitedtheearthina perfect Circle,we would see exactly fifty percent of itssurface and no more.But sinceitsorbit isthatofaslightellipse - that is,alittle bit higherat theapo-geeandlowerattheperigee - itap-pearsto"wobble" in itspassage. Whenthemoon'saxisisthustilted toward us,wecan see a fewdegreesbe-yonditsnorthpole.Whenitist i l ~ e away fromus,weareabletoseeafew degreesbeyonditssouthpole.Inthe sameway,wecanalsoobserveseveral degreesbeyond the eastern and western edgesofthemoon's"nearside."Thus, atvarioustimes,wecanseeroughly sixtypercentofitssurface,ortenper-centmorethanitstrue"earth"side. Until 1959, no one had any definite idea at all about what the How canwe' "farside"ofthe seethemoon's moonmightlook "farside"? like.Inthatyear, Russianscientistssuccessfullysentup amoonprobe,calledLunikIII,which circled the moonone time.On itsjour-. neyaroundthe"farside,"camerason Lunik III madephotographsthat were transmittedbacktolaboratorieson earth.Thesepicturesrevealedabout halfoftheunknownportionofthe moon'ssurface,leavingonlyabout twentypercentofwhichwehaveno knowledge at all. Obviously,the photographs made by LunikIIIarenotnearlyassharpand clearasthosemadeofthe "earth side" byobservatorycameras. Onlyafewformationsstandoutin legibledetail.Forthemostpartthey aretooblurredtofurnishaccuratein-formation. But, even so, the flight of the LunikIIIwasanamazingscientific break-through.ThefirstAmerican moonprobe,Ranger,willprobably have made a successful lunar voyage by thetimeyoureadthis.Rangerisex-pected to provide much clearer pictures ofwhatthemoon'shiddensurface really looks like. Moonintwopositionsofitsorbit,ill ustratingthe"wobbling." 20 N MAREFRIGORIS MAREIMBRIUM ARISTARCHUS KEPLER COPERNICUS MARETRANQUILLITATIS PTOLMEUS ALPHONSUS lYCHO DOERFEL CLAYIUS LEIBNITZ NEWTON Thevisibleside of themoon. More than30,000 .cratersare mapped,ranginginwidthfromthelargest,Baily,183milesin diameter,andClavius,146miles,tothesmallestphotographed,% mile indiameter. Thedeepest craterisNewton,29,000 feet.Thehighestmountains,LeibnitzandDoerfelexceed30,000feetandarethushigherthanthehighestmountain (Everest)onearth. Thelargest visiblevalleys are RheitaValley,115 x15miles,andAlpine Gorge.Thelargest seasareMare Imbrium(SeaofShowers)whichcoversabout340,000squaremilesandOceanusProcellarum(OceanofStorms). Theprincipalfeaturesofthemoon's surfaceareits Whatisthe mountainranges, moon-scapelike? itscraters,and its seas.Almostallofthemhavebeen given names for identification. Theseaareas,firstobservedbythe earliestastronomerslikeGalileowere givenLatinnames:OceanusProcel-larum(OceanofStorms),MareIm-brium(Sea of Rains), MareHumorum (Sea of Moisture) , MareN ubium(Sea 21 of Clouds), MareVaporum(Sea of Va-pors),MareTranquillitatis(Seaof Tranquillity), Mare F oecunditatis (Sea of Fertility), Lac us Somniorum(Sea of Dreams),and manyothers. Forthemostpart,theimportant mountain ranges were named for moun-tainsonearth:Alps,Apennines,Cau-casian,Jura,Carpathian,Pyrenees. Others,suchasLeibnitzandDoerfel, werenamedforfamousastronomers. Thecratersalsotooktheirnames fromgreatscientistsanqphilosophers, both ancient and modern:Plato, Coper-nicus,Euclid,Archimedes,Faraday, Cavendish,Ross,Pickering,Lee,New-ton,andscoresofothers. WhentheRussiansmadethefirst chartsofthemoon's"farside,"they namedtheoutstandingnewfeatures whichtheydiscovered:MoscowSea, SovietMountains,andTsiolkovsky, Lomonosov,andTsuC'hung-Chin craters. The mountains on the moon were prob-ably formed when the Whatarethemoon was in the proc-mountainson themoon?essofchangingfrom a liquid to a solid and its interior was molten. As it cooled, the surfacewrinkledandcrackedlikea skinof aprune.It wasinthis samewaythatthemountainsonearth were originally created. At one point, the Leibnitz Mountains tower 29,000 feet above their base. This isashighasMt.Everest,thetallest mountain on earth. Recent calculations, which have yet to be confirmed, indicate that. somemoonmountainsmayexist which afe even higher. Altogether,some30,000cratershave beencountedonthe Whatare thecraters?moon.Theserangein sizefromthecrater withadiameterofasmuch150 miles from rim to rim, to comparativ.ely small pock-marks less than half a mile in diameter.Thecrater,forex-ample,isabout146milesindiameter. If youwerestandinginitscenter,its rims would be invisible, completely hid-denfromviewbeyondtheshortlunar horizon. Scientistshavenowayofknowing exactly howthesecraterswerecreated. It isbelieved howeverthat someof the smalleronesmayhavebeentheresult ofvolcanicactivityduringthemoon's formativestages.Indeed,afewyears ago,oneastronomerobservedwhathe believedtobeanoutburstof gasfrom theinsideofthecraterAlphonsus.If thisobservationwascorrect,itwould indicatethattheinteriorofthemoon isstill hot and gaseous,and that apos-sibility of volcanic activity on its surface stillexists. Since only a fewlunar craters resem-ble earth volcanic-craters, it is supposed thatmostofthemwerecausedbythe tremendousimpactoflargemeteors .strikingfromouterspace.Somescien-tistsbelievethatameteorhittingthe surfaceofthemoonatananglewc;mld makeanellipticalcraterthatbecomes round due tothe heat of impact.O_ther scientists argue that whateverthe angle ofimpact,thecraterwouldberound. Thecratersonthemoonaremostly round. The sizeof themeteorsthatcreated the larger craters must have beenenor-mous, triggering explosionsmany thou-sandsoftimesgreaterthanthemost powerfulnuclearbomb.Themoonis constantlybeingbombardedbymete-ors,both large and small. Theearth,too,isunderaconstant Close-upofmooncratersintheregionof Clavius ascompared with Mount MeruCrater, an unusually well-rounded volcanic cra.ter on earth(Tanganyika, Africa)andmeteoriccratersintheUnitedStates. Thecomparisonsupportsthetheorythatmost mooncraterswerecausedbygiantmeteors. meteorbombardment.Butwhename-teorapproachesearth,itisburnedup and vaporizedasitcomesintocontact withtheheavylayersofatmosphere. Thelargeronesweseeas"shooting stars." Sometimes,if the meteor isorig-inallylargeenough,asmallcoreofit survivesandlandsonearth asachunk of metal. 23 Butsincethemoonhasnoatmos-phere,ameteorcanstrikeitwithfull force,and thusgougeout abigdepres-sionon thesurface. Thewindsandwatersofearthare constantly at work to change the earth's surfaceand erasethe marksofitsgeo-logichistory.Butthemooniswithout theerosiveeffectsofwindandwater. Thus, it is almost certain that every scar inflictedonthemoon'ssurfaceinthe pasttwoor threebillionyearsremains exactly as it was when it was first made. Scientists have not observed any new cratersofappreciablesizethathave beencreated onthe moon sincethein-ventionofthetelescope.Fromthiswe mightconcludethat themeteoricbom-bardment ofthe moon - especiallyby giantmeteors - hasnotbeenasgreat in the last fewhundred or fewthousand yearsasit wasinthedistantpast. Rillsare lessprominent featuresofthe lunarsurface.Theyare Whatare cracksintherock,some rills? shallowandsomedeep, extendinginlengthfromoneortwo milestoseveralhundred.Thesecracks were probably created when the surface of the moon cooled. 24 Someofthecircle. craters,likeCopernicus forinstance,havehuge centralpeaksandshow conspicuouslandsliding of theinnerslope. Weknowverylittleabouttherills because,comparedtothemountains andcraters,theyaretoosmalltofur-nishmuchaccuratedataforourearth camerastorecordindetail.Weknow that theyexist, and that isabout all we do know about them. Oneofthemostpuzzlingmysteriesof Whatare the"rays"? themoonscapeare the rays.Thesearebright streaksthat fanoutin alldirectionsfromsomeofthebigger craters, notably Tycho, Copernicus and Kepler,andfrommanyofthesmaller onesaswell.Someoftheseraysema-nating from Tycho are so long that they extend more than 2,000 milesfromthe crateranddisappearoverthehorizon into the moon'sfar side. Noonehaseverbeenable todeter-mine just how these rays were originally formed,orwhattheyconsistof.The mostpopulartheoryisthattheyare longstreamersofmoondustthatwere scatteredbythemeteorsthatformed thecraters. Youcanseehowthismighthave happenedifyouplaceasmallpile offinefacepowderonapieceofdark paperandthenstrikeitsharplywith I.I Ie

(e huge I'dshow 1e. Theseas,liketheMareImbrium shownhere,have no water. At top left,aretheApennineMountains. the round side of aspoon.The powder willflyout in alldirectionsinprecisely thesame pattern asthat of the rayswe canseeonthe moon. Sincethereisnoairorwindonthe moontodisturbthesedustpatterns, theywouldhaveremainedexactlyas theywerewhentheywereoriginally made. Anothertheoryholdsthattherays maybecomposedofa lighter-colored sublunar material that was blasted from thecraterbythemeteor.Theheatof the meteor's impact and explosionmay havemeltedandfusedthismaterial intoaglass-like form.Suchglassparti-cleswouldreflectlight,and thusmight accountforthefact' thatraysvaryin brightness asphases of moon change. MAREIMBRIUM The great level plain areasof the moon arecalled"seas."The Whatare earliestastronomers, the"seas"? gazingat the moon withtheirprimitivetelescopes,didnot Theraysemanating fromthebiggercraters arepuzzlingmysteries. ShownhereisTycho withraysextending morethan2,000miles fromthe crateranddis-appearingovertheho-rizonintothemoon's farside. 25 1 I 'I know that the moon was a lifeless, water-lessbody, and reasoned that parts of its surfacemustbecoveredbywaterlike the seas on earth. We know now that the "seas" are dust-covered deserts, but they have been allowed to keep their original designationsas"seas."Andindeedat onetime,whenthemoonwasbeing formed,theywereprobably actualseas of molten lava. Sincethe"seas"arefiatandappar-entlylesshostilethanthemorerugged mountainareasofthemoonscape,itis here that the first spaceships from earth, bothunmannedandmanned,areex-pected to make their initial landings. Scientistsareveryinterestedinthe Whatdowe knowaboutthe moon'ssurface.In afewyearsastro-nautswillbeland-moon 'ssurface? ingonthe moon.If theastronautsaretolandsafelyand aretoreturnfromthemoon,theywill havetobein shipsthat willbeableto landonthemoonwithoutbeingde-Photoofmoon'ssurfacetakenbySurveyorI,June, 1966.Itshowsarock,approximately6incheshigh by18incheslong,lyingafewfeetfromSurveyorI onthelunarsurface,Therockwasabout1 2feet fromtheTVcamera. 26 stroyed.Tobuildtheproperkindof moon-landingcraft,scientistsmust know on what kind of surface it is going toland.Afewyearsagosomescien-tiststhoughtthatthemoon'ssurface mightbecoveredbyalayerofdust thousandsoffeetdeep.Becausethe moonhasonlyweakgravity,thedust would not have been packed down very tightly.If aspacecrafthadlandedon thisdust,itwouldhavesunkdeepbe-neaththesurfaceofthemoon.The astronauts probably could not have left their craft andthey certainly could not have blasted off for areturn journey to earth. Someverysmoothpatchesofthe moon'ssurfacearemadeupofhard-enedlavathathasflowedfromvol-canoes.Thesewouldseemtomake good landing sites,but howthick isthe lava?Isithollowbeneath the surface? Wouldalandingspacecraftcrash throughthesurfaceandbeburied? Spacecraft builders would liketo know the answers. To find the answers, Amer-icanandRussianscientistshavebeen tryingsince19 5 8 tosendspacecraft to the moon. The earlyattemptswere mostly fail-ures.The moonbound spacecraft either fellback toearth,missedthe moon,or crashedintothemoon'ssurface,de-stroyingalltheinstrumentsonboard. The firstsuccess took place on January 2,1959,whentheRussianslaunched aspacecraftnamedMechta.Mechta circled the moon and sent back to earth pictures of the moon's far side,the first time man had ever seen that side of the moon.Mechta was also called Lunik 3, which youread about on page20. Forthenext6yearsfailuredogged themoon-surveyprograms.Then,in thelast half of1964 and thebeginning of1965,theUnitedStateshadthree brilliant successesasspacecraftnamed RangersVII,VIII,andIX tookclear, closeuppicturesofthe moon'ssurface, andsentthepicturesbacktoearthby televisionbeforecrashlandingonthe moon's surface. InFebruary,1965,theRussians crash-landedLunik IX onthemoon. Rocketsslowedthespacecraftsothat itslandingwasnotasdestructiveas formerones.Lunikcarriedashock-proofcamerawhichsent back toearth picturestakenonthemoon'ssurface. In June, 1966, a United States space-- ... - .. Paleearth-lightshines inthisartist ' sconcep-tionofanextreme close-upof agiant lunar crater withterraced walls.Thesmallercra-tersinthedust -covered floorareyounger . craft,SurveyorI,madeareallysoft landingonthemoonandsentback thousandsofpicturesofthemoon's Surveyor's pictures proved that the moon's surface was not a thick layer of dust. InthenextfewmonthsRussia launchedfourspacecrafttoorbitthe moon and send back pictures and other information.Threeofthesecraftwere successful. The United States sent three moon-orbitingcameracraftonsurvey missions.Allsentback of very clear.pictures. Many more spacecraft will be sent to explore the moon's surface before astro-nauts makethejourney tothe moon. 27 If weaccept the most popular scientific Doairand waterexiston themoon? theory,namelythat themoonandearth wereformedatthe same time and of the same basic material,thenwecantheo-rizethattheyprobablyfollowedthe same basic pattern of evolution.In this case, the moon once had an atmosphere, and alsoa form of water. Why,then,if thisatmosphereand water remained on the earth,did it not alsoremainonthemoon?Mostscien-tistsbelievethattheanswerliesinthe differencebetweentheforceofthe earth'sgravityand that ofthemoon's. The pull oftheearth'sgravitykeeps ouratmosphereandwaterfromescap-ingintospaceastheearthrotates. Butthemoon'sgravitationalpullwas not strong enoughto hold onto itsown atmosphere. Therefore, over millions of years,itsair and moisture escaped into the void of space. There is,however,atraceof atmos- phere on the moon:a fewgaseous mole-cules that cling to cracks in the surface./ Atthemostgenerousestimate,this atmosphereamountstonomorethan one-millionth that of the atmosphere on the earth's surface.Thiswould roughly beequaltotheairpressurethatexists 70!llilesabovetheearth.So,forall practical purposes, we may assume tlfa themoonisacold,lightless,airless, waterlessglobe. Moonexplorers,then,willhaveto wearclothingthatnotonlyprovides them with an oxygen supply,but which alsoprotectsthemfromthetotallack of air pressure as well as the extremes of heatandcold. 28 Doeslifeexist onthemoon? SUN a Thereare31moonsinoursolarsystem. Earth,ars,Jupiter,Saturn,Uranusand Neptune allhave satellites. Of Jupiter's12 moons,only 4arenamed;theother8are very faint. The satellites othe other_,__ P-_la_ne:-ts______ arevertinyand,itistheorized,maybe capturedasteroids. 00 Nonetheless,one of the firstass of lunarexploerswillbetobrinack samples of moon"soil"tobe tested for anyformolifethat wecouldnotob-servewithatelescope. Asfarasweknow,therearethirty moons,otherthan Arethereother ourown,revolving aroundtheother moonsinour solarsystem? eightplanetsinour SolarSystem.Marshas2;Jupiter12; Saturn9;Uranus5;. and Neptune2. Strictlypeking,thesesatellies shouldnotelledmoons,sincethe onlytruemoonisourearthsatellite. Butbecausetheyareusuallyreferred to as"moons," that iswhat wewillcall themhere. The twomoonsofMars,theplanet most similar to earth, have been named DeimosandPhobos.Botharevery tiny:Deimosisonlyfivetotenmiles indiameterandPhobosisabouttwice that size. Weknowthatthe"escapevelocity" fromearth - thespeednecessaryfor aspace vehicle to flingitself loose from 29 0 ] theearth'sfieldofgravity - isabout 25,000mph.Onlythemostpowerful rocketsinourNASAsupplyarecapa-bleofsuchatremendousthrust.But thegravityonDeimosissoweak .that amancouldjumpclearoffthetiny moon,hurlinghimselfintospaceby the power of his leg muscles alone.Any futureastronautwhomighthappento landonDeimos,willhavetobevery careful,orhemayfindhimself floating freeinouterspace. Becausethesemoonsof Marsareso small,acurioustheoryhasbeenad-vancedtoaccountforthem.Marsap-pearstobeadyingplanet,andsome people think itoncehad an atmosphere likeoursandwaspopulatedbyintelli-gentbeings.Whentheatmosphere thinnedout,makinglifeontheplanet impossible(sothetheorygoes),the Mars-menbuilttwogiant spaceshipsin whichthey could continue tolive under artificialconditions,andputtheminto orbit.These man-mademoonsare Dei-mosandPhobos- ifthefantastic theory istrue.. Galileo,aswehavelearned,discov-eredthefourlargestmoonsofJupiter. ThesehavebeennamedIo,Europa, Ganymede, and Callisto. Io is about the sizeofourmoon;Europaisslightly smaller,andtheothertwoareslightly larger.The firstthreeseemtobe made of rock, like our moon, but it ispossible that Callisto maybeasolid ballof ice, or perhaps a rock core covered with ice. Duringrecentyears,astronomers havedetectedeightmoremoonsorbit-ingaroundJupiter.Allofthemare small,ranginginsizefrom20to150 milesindiameter. 30 Saturnhasnineknownmoons.The largestone,Titan,isthebiggestmoon inour solarsystem.It isaboutthesize of Mars, and appears to have an atmos-phere of its own,probably composed of methanegas.Itisbelievedthatsome of Saturn's smaller moonsmaybe,like Callisto,nothingbut ballsofice. Inadditiontoitsnine moons, Saturn also is surrounded by a spectacular ring. This ring iscomposed of billions of tiny moons,ranginginsizefromspecksof dusttobaseballs.Sincetheringsare goodreflectorsofl i ~ h t itisthought thattheytooaretinyiceballsorice-covered rocks. We know verylittle about the moons ofUranusandNeptune,except forthe factthatUranushasfiveandNeptune two.ThesmallerofNeptune'smoons, Neireid,isonlyabout200milesin diameter.The larger,Triton, isagiant, itsdiameterbeingbetween3,000and 5,800miles. Butofallthemoonsinthesky,the onethatinterestsusmostisourown. If weacceptthetheorythatthemoon wasformedfrom Doesthemoon .thesamebasic ma-containvaluable terialsasthe earth, minerals? thenwemayas-sume that it contains much of the same elementsthat are foundonearth:iron, aluminum, lead, nickel, nitrogen, hydro-gen,.etc.Oneofthemainreasonsfor sending manned spacecraft to the moon willbe to determine exactly what kinds ofmetalsandmineralsdoexistthere; in what quantities they are to be found; and what isthe pest waytomine them. Themetaldepositsoftheearthare graduallydiminishing,althoughitwill probablybethousandsofyearsbefore they are completely exhausted.But sci-entists look to the deposits on the moon toproviderawmaterialsforearth'sin-dustries well into the distant future. One leadingauthorityhassuggested that large deposits of ice and water may lie only a fewdozen,or afewhundred, feetbeneaththelunarsurface.If this isso,these deposits can furnish supplies of water for moon explorers to drink -and,bytherelativelysimpleprocessof electrolysis(thechemicalbreakdown ofwaterintoitscomponentpartsof hydrogenandoxygen) ,suppliesof oxygen forthem to breathe. Formanycenturiesmanhasdreamed Whydowewant toexplore a wistful dream of somedaygoingto themoon.Butit themoon? wasnotuntilthe pastfewyearsthatmoderndevelop-mentsinrocketengineshavemade suchanattemptfeasible.TheUnited StatesNationalAeronauticsandSpace Agency(NASA) ,andtheRussian spaceagency,arealreadyplanningfor the great adventure. Manypeoplehaveasked:"Whyis itworthspendingbillionsofdollarsto land teamsof explorersonthemoon?" Thereareanumberofreasons. Whileastronomersalreadyknowa greatdealaboutthesurfaceofthe moon, there is much that telescopes and radar beams cannot disclose.Is the dust Themoon-suitwhichwastestednottoo longagoinalavacraterinCalifornia,is pressurizedand carries oxygen and food . coverthinor thick?Isthere acrust?Is the surface foamy? What kind of rocks, ores,andothermineralsandelements doesthemooncontain?Whatisthe "soil'; of the moon like? Does it contain dormantlife?Whatistheexacteffect ofsolarradiationuponthelunarsur-fa'ce?Doesthemooncontainsub-surfaceiceandwater? Isitsafeforhumanbeingstofly throughbeltsofradiationthatmaybe deadly?Canspaceshipstravelthrough cloudsofmeteoritesandothercosmic debristhatwhizzthroughspaceat velocitiesofupto25,000milesper hour? Normally,theinstrumentsofun-manned spacecraft can discover the an-swerstosuchquestionsasthesemore reliably than a man.But a machine can onlydowhatithasbeenbuilttodo. Itcannotcopewiththeunexpected. Onlymancanhandletheunforeseen. Thatisonereasonwhyscientistsfeel that man must go to the moon. Thesurfaceoftheearthliesatthe bottomofadeep,heavyseaofatmos-phere.Througheventhefinest,most powerfultelescopesthatmanhasbeen able to produce, the pictures of the stars - andevenofthemoonitself- are more or lessdistorted. Themoon'salmosttotallackofat-mosphere,and thusofatmosphericdis-tortions,makeittheideallocationfor anastronomicalobservatory.Astrono-merssay that arelativelysmall20-inch telescopeontpemoonwouldaccom-plishasmuchinprobingthemysteries of outer space as the giant 200-inch tele-scopeatMountPalomar,theworld's largest.Andifa200-inchtelescope 32' couldbeplacedinanobservatoryon the moon, the possibility of furtherdis-coveries would be endless. Ithasbeenpointedoutthatthe moon'ssurface,andeverygeological moon-mark upon it, has in all likelihood remainedunchangedforbillionsof years.There hasbeen nowind,noero-sion, no weather to change them,as has beenthecaseonearth.Thereforesci-entistsarehopefulthatthischangeless record of the moon's history may go far toanswer manyofthepuzzling riddles abouttheoriginanddevelopmentof the solar system asawhole. Withitslowgravityandabsenceof atmosphere,themoonwouldbeanal-most perfect way-station from which to launchspaceshipstotheotherplanets. Less than one-sixth of the escape veloc-itywouldberequiredtoliftavehicle offthemoonthanwouldbeneededto liftitoffalaunchingpadonearth. This tremendousdifference in pay-load wouldallowtheshiptocarry infinitely muchmorefuelformaneuveringonce it was in s ~ a c e .Already,ourspacescientistsare lookingforwardtothedaywhenthe moonwillbecometheearth'sgreat spaceport. Asmentionedearlier,minerologists believethattheoresandmetalswhich are almost sure to be found on the moon Artist'sconceptionofamoon-city.Fantastic?Yes. ButlesssothanJulesVerne'snovelin1874"From the EarthtotheMoon ." One of theillustrationsof the novelshowedthemoonshipafterlanding,andthe passengersobservingtheUniverse(insetabove). can provide a nearly limitlesssource of rawmaterialsforearth'sindustries. Oncepermanentlandingshavebeen madeonthe moon,methodsofmining andtransportingthesemineralsshould quicklyfollow. Finally, it has always been the nature of man to want to explore the unknown. Because of this urge, the early sea-farers foundtheNewWorld;Americanpio-neersdiscoveredanddevelopedthe great country that lay over thewestern mountains;Arcticadventurersopened both the north and south polar areasto exploration. Afamousmountainclimberwas once askedwhyhewanted toscalethe dangerousheightsofMountEverest. He replied simply:"Because it is there." That isundoubtedly one of the reasons whymenwanttolandonthemoon. Justbecauseitisthere. Thesearethemissilesthatareusedtopreparethe researchandwillbeusedtoattemptthemoonland-ing.Fromlefttoright:TheAtlasusedinProject Mercury,whichsentourastronautsintoorbitaround the earth; the Titan, used in Project Gemini,which will perfectthetechniquesofmeetingwithtankerswhile inorbit;theSaturnC-1,usedtotestApollocompon-entsandtheAdvanced Saturn, whichwillbe usedfor ProjectApollo,themannedlandingonthemoon. The missiles are compared in size with the Washington MonumentinWashington,D.C.,towering555feet. TheAdvancedSaturnwillbeabout350feethigh, higher thantheStatue of LibertyinNew Yorkharbor. 34 Itisinevitablethatthefirstcrewof How will spacementhatlandson the moon will be likened mengettoCC themoon?tohristopherolum-bus.Andinmanyre-spectsthiswillbetrue.Theywillhave pioneeredthewayacrossadangerous andforbiddingsea - inthiscasethe seaofspace - andwillhavesetfoot uponahostilesoilthatnomanhas everseenbefore. ButwhereasColumbuscouldonly guess at what he would find,the pioneer spacemen will have a good idea of what toexpect.In1492,mostmenbelieved thattheearthwasflat,andthat ifa shipsailedtoitsedge,it wouldplunge offintosomefearful,bottomlessabyss andbe lost forever.Theyalsothought that the sea was guarded by fiercemon-stersthatcouldswallowashipandits crewatonegulp.Columbusdidnot believethesefancifultales,but hehad to riskhisownlifeand the livesofhis crew to prove that he was right. The unknownintowhichourspace-menwillventurewillpresentdangers muchmorerealthanthosewhichCo-lumbusfaced.Evenwithasmuch knowledgeaswealreadyhaveabout themoon,westillcannotbesurethat a spaceship,making its firstlunar land-ing,willnot sink hundredsof feetinto aquicksand- ofloosedustorfrozen foam.Wedonotknowtheextentor deadly effectsofsolar radiation onthe moon'ssurface.Theanswerstothese anddozensofotherquestionsjustas vitalcanmeanthedifferencebetween lifeanddeathtoourmoonpioneers. But whereasColumbus had to findout all the answers for himself, the National AeronauticsandSpaceAdministration is planning to send out a seriesof robot spacemen,unmannedvehiclesthatare crammed with scientific instruments,to eliminate as much of the guesswork and dangeraspossiblebeforetl!efirstmen try for a landing.Alre&dy,the valueof firstsendingunmannedcrafttothe moonhasbeenamplydemonstrated. Twosuchvehicles,aimedatacrash Woomera, Australia and Johannes-burg,SouthAfrica,will helptrackthespace vehiclesandreportto Goldstone(above), Southern California,the Ranger's command post. Orderstothespace craft are sent,andtele-visionpicturesandsig-nalsfromRangerare received,byan85-foot dishantenna. At left the blast-offofanAtlas missilewithRanger4 mountedabove thesec-ond-stage Agena 8. landingonthemoon,havethusfar failed. The first one missed the moon by about22,000milesandwentintoper-manentorbitaroundthesun.Thesec-ondlostitspower.Inbothcases,had they been manned by human crews,the crewssurely would have been lost. Thefirstunmannedmoonprobes plannedbyNASAare Whatare thR ? knownasRangers. eangers. Accordingtopresent plans,therewillbeseveraltypesof 35 Ranger,thespacerobot,onitswayto the moon to assemble informationneces-saryforthemenwhowillfollowlater . Theinstrumentpackage, alreadyseparatedfromits carrier,issloweddownby aretrorockettosoften theimpactofthecrash. Thebalsaball,flattenedbyinpact(instrumentpackageex-posedincutawayillustration),comestorestonthesurface of themoon . Themoon-shot of Ranger,orig-inallyplannedfor1962,had toberescheduledfor1963. vehiclesinthisclass.Itisverylikely that the first one willhave made a moon landingbeforeyoureadthesewords. The Ranger willbe asmallbut com-plicatedvehicle.Inonesectionitwill carryatelevisioncamera,andinstru-mentstodetectradiationandother lunarphenomena.It willalsocarryan instrumentedcapsulethatwillactually make asafe moonlanding.Ranger will work like this: Afterbeingliftedoffitslaunching pad at Cape Canaveral by a giant Atlas rocket,itwillbehurledintoanearth orbitbyabooster rocketata.speedof 12,600MPH.Halfwayaroundthe world,atapointaboveSouthAfrica, asecondblastfromtheboosterwill thrust it into a moon trajectory.At this pointitsspeedwillhaveincreasedto 24,500MPH,sufficienttoallowitto escapefromanearthorbitandhead out into empty space.At thispoint,the booster rocket will drop off, and Ranger willbe on itsown. Nowtheamazinglyintricate ~ t r u mentswillbegintounfold.Wing-like panelswillspringoutfromitssides. . Thesepanelswillcaptureenergyfrom thesuntobeturnedintoelectricityto powertheRanger'sTVandradio equipment.Withtheradioworking, Rangerwillbeabletobecontrolled fromgroundstationsonearth.Bythe aid of small guidance rockets,the robot willbeputonaprecisecoursefora moonlanding. As it approaches the moon'ssurface, some66hoursafterlaunching,TV cameraswillbegintakingthefirst close-up pictures of the moon. While sci-entistsusingearth-boundtelescopes cannot seemoon-objectslessthanhalf-a-milelong,Ranger'scamerawillbe abletorecordobjectsnolargerthana dining-roomtable.The pictureswillbe radioedtoearthasrapidlyastheyare taken,andforthefirsttimescientists willknowwhatthelunarsurfacelooks like inminutedetail. Nowthemostamazingpartofthe Rangerwillgotowork. WhatistheI..11 . balsaball?tstipw1uncoverit-self,exposingablue-and-whiteballmadeofbalsawood, abouthalfagainaslargeasabasket-ball. AtthispointRangerwillbefalling into the moon at a speed of about 6,000 .37 V.ariousU.S.companiendix,GeneralMotorsandothers, havealreadydesignei:Iandprogressedtotheworking-model stageof anmber of moonvehicles . Theyaredesignedforspecial-jedexplorationaltasks,afterhavinglandedonthemoon,and are all equipped withinstruments to report the findings back to earth. MPH; and thisspeed willbe increasing everysecondduetothepullofthe moon'sgravity. When the Ranger is some 70,000 feet above the moon, a retrorocket will blast the balsa ball away from the main body. The retarding forceofthislittle rocket will bring the ball toamomentary stop at amoon-altitudeofabout1,000 feet. Thentherocketwilljettisonitselfand theballwillfallfreetothesurface below. Meanwhile,thecamerasonRanger willcontinuetotakeclose-uppictures ofthemoonandrelaythembackto earth until Ranger strikes the rocky sur-faceandiscompletelydisintegrated uponimpact. Beginning its fall all over again, from its temporary stop at 1,000 feet,the ball willstrikethemoon'ssurfacewitha 38 speed of no more than150 MPH. Since theballwasbuilttowithstandthis much of ajar(this hasbeen proved by droppingitfromairplanes),itwill probably bounce once or twice and then roll toastop - the firstman-madeob-jectevertolandsafelyonthemoon! Theballitselfismadeofsegmentsof balsa, the lightest and Whatwillthe.. balltellus?mostres1hentofall woods,whicharefit-ted together in such away asto be best abletoabsorbthejoltoflanding.Its peculiarpaintpatternisdesignedto reflectandabsorblunarsunlight,and thushelpoffset the moon'sextremesof heat and cold. Insidetheballisaseismometer,an earthquake(orinthis. caseamoon-quake)recorder,andaradiotransmit-ter. This seismometer can show us many thingsabout the mysteriesof the moon. 1' I (1 I