pale blue dot -carl sagan- 第3部分

Obediently；　it　turned　its　cameras　back　toward　the　now…distant　planets。　Slewing　its　scan　platform　from　one　spot　in　the　sky　to　another；　it　snapped　60　pictures　and　stored　them　in　digital　form　on　its　tape　recorder。　Then；　slowly；　in　March；　April；　and　May；　it　radioed　the　data　back　to　Earth。　Each　image　was　posed　of　640；000　individual　picture　elements　（〃pixels〃）；　like　the　dots　in　a　newspaper　wire…photo　or　a　pointillist　painting。　The　spacecraft　was　3。7　billion　miles　away　from　Earth；　so　far　away　that　it　took　each　pixel　5？　hours；　traveling　at　the　speed　of　light；　to　reach　us。　The　pictures　might　have　been　returned　earlier；　but　the　big　radio　telescopes　in　California；　Spain；　and　Australia　that　receive　these　whispers　from　the　edge　of　the　Solar　System　had　responsibilities　to　other　ships　that　ply　the　sea　of　space　among　them；　Magellan；　bound　for　Venus；　and　Galileo　on　its　tortuous　passage　to　Jupiter。

Voyager　1　was　so　high　above　the　ecliptic　plane　because；　in　1981；　it　had　made　a　close　pass　by　Titan；　the　giant　moon　of　Saturn。　Its　sister　ship；　Voyager　2；　was　dispatched　on　a　different　trajectory；　within　the　ecliptic　plane；　and　so　she　was　able　to　perform　her　celebrated　explorations　of　Uranus　and　Neptune　The　two　Voyager　robots　have　explored　four　planets　and　nearly　sixty　moons。　They　are　triumphs　of　human　engineering　an。　one　of　the　glories　of　the　American　space　program。　They　will　be　in　the　history　books　when　much　else　about　our　time　forgotten。

The　Voyagers　were　guaranteed　to　work　only　until　the　Saturn　encounter。　I　thought　it　might　be　a　good　idea；　just　after　Saturn；　to　have　them　take　one　last　glance　homeward。　From　Saturn；　I　knew　the　Earth　would　appear　too　small　for　Voyager　to　make　out　any　detail。　Our　planet　would　be　just　a　point　of　light；　a　lonely　pixel；　hardly　distinguishable　from　the　many　other　points　of　light　Voyager　could　see；　nearby　planets　and　far…off　suns。　But　precise　because　of　the　obscurity　of　our　world　thus　revealed；　such　picture　might　be　worth　having。

Mariners　had　painstakingly　mapped　the　coastlines　of　the　continents。　Geographers　had　translated　these　findings　into　charts　and　globes。　Photographs　of　tiny　patches　of　the　Earth　had　been　obtained　first　by　balloons　and　aircraft；　then　by　rockets　in　brief　ballistic　flight；　and　at　last　by　orbiting　spacecraft—giving　a　perspective　like　the　one　you　achieve　by　positioning　your　eyeball　about　an　inch　above　a　large　globe。　While　almost　everyone　is　taught　that　the　Earth　is　a　sphere　with　all　of　us　somehow　glued　to　it　by　gravity；　the　reality　of　our　circumstance　did　not　really　begin　to　sink　in　until　the　famous　frame…filling　Apollo　photograph　of　the　whole　Earth—the　one　taken　by　the　Apollo　17　astronauts　on　the　last　journey　of　humans　to　the　Moon。

It　has　bee　a　kind　of　icon　of　our　age。　There's　Antarctica　at　what　Americans　and　Europeans　so　readily　regard　as　the　bottom；　and　then　all　of　Africa　stretching　up　above　it：　You　can　see　Ethiopia；　Tanzania；　and　Kenya；　where　the　earliest　humans　lived。　At　top　right　are　Saudi　Arabia　and　what　Europeans　call　the　Near　East。　Just　barely　peeking　out　at　the　top　is　the　Mediterranean　Sea；　around　which　so　much　of　our　global　civilization　emerged。　You　can　make　out　the　blue　of　the　ocean；　the　yellow…red　of　the　Sahara　and　the　Arabian　desert；　the　brown…green　of　forest　and　grassland。

And　yet　there　is　no　sign　of　humans　in　this　picture；　not　our　reworking　of　the　Earth's　surface；　not　our　machines；　not　ourselves：　We　are　too　small　and　our　statecraft　is　too　feeble　to　be　seen　by　a　spacecraft　between　the　Earth　and　the　Moon。　From　this　vantage　point；　our　obsession　with　nationalism　is　nowhere　in　evidence。　The　Apollo　pictures　of　the　whole　Earth　conveyed　to　multitudes　something　well　known　to　astronomers：　On　the　scale　of　worlds—to　say　nothing　of　stars　or　galaxies—humans　are　inconsequential；　a　thin　film　of　life　on　an　obscure　and　solitary　lump　of　rock　and　metal。

It　seemed　to　me　that　another　picture　of　the　Earth；　this　one　taken　from　a　hundred　thousand　times　farther　away；　might　help　in　the　continuing　process　of　revealing　to　ourselves　our　true　circumstance　and　condition。　It　had　been　well　understood　by　the　scientists　and　philosophers　of　classical　antiquity　that　the　Earth　was　a　mere　point　in　a　vast　enpassing　Cosmos；　but　no　one　had　ever　seen　it　as　such。　Here　was　our　first　chance　（and　perhaps　also　our　last　for　decades　to　e）。

Many　in　NASA's　Voyager　Project　were　supportive。　But　from　the　outer　Solar　System　the　Earth　lies　very　near　the　Sun；　like　a　moth　enthralled　around　a　flame。　Did　we　want　to　aim　the　camera　so　close　to　the　Sun　as　to　risk　burning　out　the　spacecraft's　vidicon　system？　Wouldn't　it　be　better　to　delay　until　all　the　scientific　images　from　Uranus　and　Neptune；　if　the　spacecraft　lasted　that　long；　were　taken？

And　so　we　waited—　and　a　good　thing　too—from　1981　at　Saturn；　to　1986　at　Uranus；　to　1989；　when　both　spacecraft　had　passed　the　orbits　of　Neptune　and　Pluto。　At　last　the　time　came　But　there　were　a　few　instrumental　calibrations　that　needed　to　be　done　first；　and　we　waited　a　little　longer。　Although　the　spacecraft　were　in　the　right　spots；　the　instruments　were　still　working　beautifully；　and　there　were　no　other　pictures　to　take；　a　few　project　personnel　opposed　it。　It　wasn't　science；　they　said。　Then　we　discovered　that　the　technicians　who　devise　and　transmit　the　radio　mands　to　Voyager　were；　in　a　cash…strapped　NASA；　to　be　laid　off　immediately　or　transferred　to　other　jobs。　If　the　picture　were　to　be　taken；　it　had　to　be　done　right　then。　At　the　last　minute　actually；　in　the　midst　of　the　Voyager　2　encounter　with　Neptune；　the　then　NASA　Administrator；　Rear　Admiral　Richard　Truly；　stepped　in　and　made　sure　that　these　images　were　obtained。　The　space　scientists　Candy　Hansen　of　NASA's　Jet　Propulsion　Laboratory　（JPL）　and　Carolyn　Porco　of　University　of　Arizona　designed　the　mand　sequence　and　calculated　the　camera　exposure　times。

So　here　they　are—a　mosaic　of　squares　laid　down　on　top　of　the　planets　and　a　background　smattering　of　more　distant　stars。　We　were　able　to　photograph　not　only　the　Earth；　but　also　five　other　of　the　Sun's　nine　known　planets。　Mercury；　the　innermost；　was　lost　in　the　glare　of　the　Sun；　and　Mars　and　Pluto　were　too　small；　too　dimly　lit；　and/or　too　far　away。　Uranus　and　Neptune　are　so　dim　that　to　record　their　presence　required　long　exposures；　accordingly；　their　images　were　smeared　because　of　spacecraft　motion。　This　is　how　the　planets　would　look　to　an　alien　spaceship　approaching　the　Solar　System　after　a　long　interstellar　voyage。

From　this　distance　the　planets　seem　only　points　of　light；　smeared　or　unsmeared—even　through　the　high…resolution　telescope　aboard　Voyager。　They　are　like　the　planets　seen　with　the　naked　eye　from　the　surface　of　the　Earth—luminous　dots；　brighter　than　most　of　the　stars。　Over　a　period　of　months　the　Earth；　like　the　other　planets；　would　seem　to　move　among　the　stars。　You　cannot　tell　merely　by　looking　at　one　of　these　dots　what　it's　like；　what's　on　it；　what　its　past　has　been；　and　whether；　n　this　particular　epoch；　anyone　lives　there。

Because　of　the　reflection　of　sunlight　off　the　spacecraft；　the　Earth　seems　to　be　sitting　in　a　beam　of　light；　as　if　there　were　some　special　significance　to　this　small　world。　But　it's　just　an　accident　of　geometry　and　optics。　The　Sun　emits　its　radiation　equitably　in　all　directions。　Had　the　picture　been　taken　a　little　earlier　or　a　little　later；　there　would　have　been　no　sunbeam　highlighting　the　Earth。

And　why　that　cerulean　color？　The　blue　es　partly　from　the　sea；　partly　from　the　sky。　While　water　in　a　glass　is　transparent；　It　absorbs　slightly　more　red　light　than　blue。　If　you　have　tens　of　meters　of　the　stuff　or　more；　the　red　light　is　absorbed　out　and　what　gets　reflected　back　to　space　is　mainly　blue。　In　the　same　way；　a　short　line　of　sight　through　air　seems　perfectly　transparent。　Nevertheless—something　Leonardo　da　Vinci　excelled　at　portraying—the　more　distant　the　object；　the　bluer　it　seems。　Why？　Because　the　air　scatters　blue　light　around　much　better　than　it　does　red。　So　the　bluish　cast　of　this　dot　es　from　its　thick　but　transparent　atmosphere　and　its　deep　oceans　of　liquid　water。　And　the　white？　The　Earth　on　an　average　day　is　about　half　covered　with　white　water　clouds。

We　can　explain　the　wan　blueness　of　this　little　world　because　we　know　it　well。　Whether　an　alien　scientist　newly　arrived　at　the　outskirts　of　our　solar　system　could　reliably　deduce　oceans　and　clouds　and　a　thickish　atmosphere　is　less　certain。　Neptune；　for　instance；　is　blue；　but　chiefly　for　different　reasons。　From　this　distant　vantage　point；　the　Earth　might　not　seem　of　any　particular　interest。

But　for　us；　it's　different。　Look　again　at　that　dot。　That's　here。　That's　home。　That's　us。　On　it　everyone　you　love；　everyone　you　know；　everyone　you　ever　heard　of；　every　human　being　who　ever　was；　lived　out　their　lives。　The　aggregate　of　our　joy　and　suffering；　thousands　of　confident　religions；　ideologies；　and　economic　doctrines；　every　hunter　and　forager；　every　hero　and　coward；　every　creator　and　destroyer　of　civilization；　every　king　and　peasant；　every　young　couple　in　love；　every　mother　and　father；　hopeful　child；　inventor　and　explorer；　every　teacher　of　morals；　every　corrupt　politician；　every　〃superstar；”　every　〃supreme　leader；〃　every　saint　and　sinner　in　the　history　of　our　species　lived　there—on　a　mote　of　dust　suspended　in　a　sunbeam。

The　Earth　is　a　very　small　stage　in　a　vast　cosmic　arena。　Think　of　the　rivers　of　blood　spilled　by　all　those　generals　and　emperors　so　that；　in　glory　and　triumph；　they　could　bee　momentary　masters　of　a　fraction　of　a　dot。　Think　of　the　endless　visited　by　the　inhabitants　of　one　corner　of　this　pixel　the　scarcely　distinguishable　inhabitants　of　some　other　corner；　how　frequent　their　misunderstandings；　how　eager　they　are　to　kill　one　another；　how　fervent　their　hatreds。

Our　posturings；　our　imagined　self…importance；　the　delusion　that　we　have　some　privileged　position　in　the　Universe；　are　challenged　by　this　point　of　pale　light。　Our　planet　is　a　lonely　speck　in　the　great　enveloping　cosmic　dark。　In　our　obscurity；　in　all　this　vastness；　there　is　no　hint　that　help　will　e　from　elsewhere　to　save　us　from　ourselves。

The　Earth　is　the　only　world　known　so　far　to　harbor　life。　There　is　nowhere　else；　at　least　in　the　near　future；　to　which　our　species　could　migrate。　Visit；　yes。　Settle；　not　yet。　Like　it　or　not；　for　the　momen