it； and all the nations responsible seem mitted to the project。 Perhaps it will actually e about。 Perhaps winging across the billion miles of intervening interplanetary space will be； in the not too distant future。 news about how far along the path to life Titan has e。
CHAPTER 8 THE FIRST NEW PLANET
1 implore you； you do not hope to be able to give the reasons for the number of planets； do you？ This worry has been resolved 。 。 。
— JOHANNES KEPLER； EPITOME OF COPERNICAN ASTRONOMY； BOOK 4 / 1621
Before we invented civilization； our ancestors lived mainly in the open； out under the sky。 Before we devised artificial lights and atmospheric pollution and modern forms of nocturnal entertainment； we watched the stars。 There were practical calendrical reasons； of course； but there was more to it than that。 Even today； the most jaded city dweller can be unexpectedly moved upon encountering a clear night sky studded with thousands of twinkling stars。 When it happens to me after all these years； it still takes my breath away。
In every culture； the sky and the religious impulse are intertwined。 I lie back in an open field and the sky surround me。 I'm overpowered by its scale。 It's so vast and so far away that my own insignificance bees palpable。 But I don't feel rejected by the sky。 I'm a part of it； tiny； to be sure； but everything is tiny pared to that overwhelming immensity； And when I concentrate on the stars； the planets； and their motions； I have an irresistible sense of machinery； clockwork； elegant precision working on a scale that； however lofty our aspirations； dwarfs and humbles us。
Most of the great inventions in human history—from stone tools and the domestication of fire to written language—were made by unknown benefactors。 Our institutional memory of long…gone events is feeble。 We do not know the name of that ancestor who first noted that planets were different from stars。 She or he must have lived tens； perhaps even hundreds of thousands of years ago。 But eventually people all over the world understood that five； no more； of the bright points of light that grace the night sky break lockstep with the others over a period of months； moving strangely…almost as if they had minds of their own。
Sharing the odd apparent motion of these planets were the Sun and Moon； making seven wandering bodies in all。 These seven were important to the ancients； and they named them after gods not any old gods； but the main gods； the chief gods； the ones who tell other gods （and mortals） what to do。 One of the planets； bright and slow…moving； was named by the Babylonians after Marduk； by the Norse after Odin； by the Greeks after Zeus； and by the Romans after Jupiter； in each case the king of the gods。 The faint； fast…moving one that was never far from the Sun the Romans named Mercury； after the messenger of the gods； the most brilliant of them was named Venus； after the goddess of love and beauty； the blood red one Mars； after the god of war； and the most sluggish of the bunch Saturn； after the god of time。 These metaphors and allusions were the best our ancestors could do： They possessed no scientific instruments beyond the naked eye； they were confined to the Earth； and they had no idea that it； too； is a planet。*
* There was one moment in the last 4；000 years when all seven of these celestial bodies were clustered tightly together。 Just before dawn on March 4； 1953 B。C。； the crescent Moon was at the horizon。 Venus； Mercury； Mars； Saturn； and Jupiter were strung out like jewels on a necklace near the great square in the constellation Pegasus—near the spot from which in our time the Perseid meteor shower emanates。 Even casual watchers of the sky must have been transfixed by the event。 What was it—a munion of the gods？ According to the astronomer David Pankenier of Lehigh University and later Kevin Pang of JPL； this event was the starting point for the planetary cycles of the ancient Chinese astronomers。 There is no other time in the last 4；000 years （or in the next） when the dance of the planets around the Sun brings them so close together from the vantage point of Earth。 But on May 5； 2000； all seven will be visible in the same part of the sky—although some at dawn and some at dusk and about ten times more spread out than on that late winter morning in 1953 B。C。 Still； it's Probably a good night for a party。
When it got to be time to design the week—a period of time； unlike the day； month； and year； with no intrinsic astronomical significance—it was assigned seven days； each named after one of the seven anomalous lights in the night sky。 We can readily make out the remnants of this convention。 In English； Saturday is Saturn's day。 Sunday and Mo＇o＇nday are clear enough。 Tuesday through Friday are named after the gods of the Saxon and kindred Teutonic invaders of Celtic/Roman Britain： Wednesday； for example； is Odin's （or Wodin's） day； which would be more apparent if we pronounced it as it's spelled； 〃Wedn's Day〃； Thursday is Thor's day； Friday is the day of Freya； goddess of love。 The last day of the week stayed Roman； the rest of it became German。
In all Romance languages； such as French； Spanish； and Italian； the connection is still more obvious； because they 4 derive from ancient Latin； in which the days of the week were named （in order； beginning with Sunday） after the Sun； the Moon； Mars； Mercury； Jupiter； Venus； and Saturn。 （The Sun's day became the Lord's day。） They could have named the days in order of the brightness of the corresponding astronomical bodies—the Sun； the Moon； Venus； Jupiter； Mars； Saturn； Mercury （and thus Sunday； Monday； Friday； Thursday； Tuesday； Saturday； Wednesday）—but they did not。 If the days of the week in Romance languages had been ordered by distance from the Sun； the sequence would be Sunday； Wednesday； Friday； Monday； Tuesday； Thursday； Saturday。 No one knew the order of the planets； though； back when we were naming planets； gods； and days of the week。 The ordering of the days of the week seems arbitrary； although perhaps it does acknowledge the primacy of the Sun。
This collection of seven gods； seven days； and seven worlds the Sun； the Moon； and the five wandering planets entered the perceptions of people everywhere。 The number seven began to acquire supernatural connotations。 There were seven 〃heavens；〃 the transparent spherical shells； centered on the Earth； that were imagined to make these worlds move。 The outermost—the seventh heaven—is where the 〃fixed〃 stars were imagined to reside。 There are Seven Days of Creation （if we include God's day of rest）； seven orifices to the head； seven virtues； seven deadly sins； seven evil demons in Sumerian myth。 seven vowels in the Greek alphabet （each affiliated with a planetary god）； Seven Governors of Destiny according to the Hermetists； Seven Great Books of Manichaeism； Seven Sacraments； Seven Sages of Ancient Greece； and seven alchemical 〃bodies〃 （gold； silver； iron； mercury； lead； tin； and copper—gold still associated with the Sun； silver with the Moon； iron with Mars； etc。）。 The seventh son of a seventh son is endowed with supernatural powers。 Seven is a 〃lucky〃 number。 In the New Testament's Book of Revelations； seven seals on a scroll are opened； seven trumpets are sounded； seven bowls are filled。 St。 Augustine obscurely argued for the mystic importance of seven on the grounds that three 〃is the first whole number that is odd〃 （what about one？）； 〃four the first that is even〃 （what about two？）； and 〃of these 。 。 。 seven is posed。〃 And so on。 Even in our time these associations linger。
The existence even of the four satellites of Jupiter that Galileo discovered—hardly planets—was disbelieved on the grounds that it challenged the precedence of the number seven。 As acceptance of the Copernican system grew； the Earth was added to the list of planets； and the Sun and Moon were removed。 Thus； there seemed to be only six planets （Mercury； Venus； Earth； Mars； Jupiter； and Saturn）。 So learned academic arguments were invented showing why there had to be six。 For example； six is the first 〃perfect〃 number； equal to the sum of its divisors （1 ＋ 2 ＋ 3）。 Q。E。D。 And anyway； there were only six days of creation； not seven。 People found ways to acmodate from seven planets to six。
As those adept at numerological mysticism adjusted to the Copernican system； this self…indulgent mode of thinking spilled over from planets to moons。 The Earth had one moon； Jupiter had the four Galilean moons。 That made five。 Clearly one was missing。 （Don't forget： Six is the first perfect number。） When Huygens discovered Titan in 1655； he and many others convinced themselves that it was the last： Six planets； six moons； and God's in His Heaven。
The historian of science I。 Bernard Cohen of Harvard University has pointed out that Huygens actually gave up searching for other moons because it was apparent； from such arguments； that no more were to be found。 Sixteen years later； ironically with Huygens in attendance； G。 D。 Cassini* of the Paris Observatory discovered a seventh moon—Iapetus； a bizarre world with one hemisphere black and the other white； in an orbit exterior to Titan's。 Shortly after； Cassim discovered Rhea； the next Saturnian mo