s 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 moon interior to Titan。
* After whom the European…American mission to the Saturn system is named。
Here was another opportunity for numerology； this time harnessed to the practical task of flattering patrons。 Cassim added up the number of planets （six） and the number of satellites （eight） and got fourteen。 Now it so happened that the man who built Cassim's observatory for him and paid his salary was Louis XIV of France； the Sun King。 The astronomer promptly 〃presented〃 these two new moons to his sovereign and proclaimed that Louis's 〃conquests〃 reached to the ends of the Solar System。 Discreetly； Cassim then backed off from looking for more moons； Cohen suggests he was afraid one more might now offend Louis—a monarch not to be trifled with； who would shortly be throwing his subjects into dungeons for the crime of being Protestants。 Twelve years later； though； Cassim returned to the search and found—doubtless with a measure of trepidation—another two moons。 （It is probably a good thing that we have not continued in this vein； otherwise France would have been burdened by seventy…some…odd Bourbon kings named Louis。）
WHEN CLAIMS OF NEW WORLDS WERE MADE In the late eighteenth century； the force of such numerological arguments had much dissipated。 Still； it was with a real sense of surprise that people heard in 1781 about a new planet； discovered through the telescope。 New moons were paratively unimpressive； especially after the first six or eight。 But that there were new planets to be found and that humans had devised the means to do so were both considered astonishing； and properly so。 If there is one previously unknown planet； there may be many more—in this solar system and in others。 Who can tell what might be found if a multitude of new worlds are hiding in the dark？
The discovery was made not even by a professional astronomer but by William Herschel； a musician whose relatives had e to Britain with the family of another anglified German； the reigning monarch and future oppressor of the American colonists； George III。 It became Herschel's wish to call the planet George （〃George's Star；〃 actually）； after his patron。 but； providentially； the name didn't stick。 （Astronomers seem to have been very busy buttering up kings。） Instead； the planet that Herschel found is called Uranus （an inexhaustible source of hilarity renewed in each generation of English…speaking nine…year…olds）。 It is named after the ancient sky god who； according to Greek myth； was Saturn's father and thus the grandfather of the Olympian gods。
We no longer consider the Sun and Moon to be planets； and ignoring the paratively insignificant asteroids and ets； count Uranus as the seventh planet in order from the Sun （Mercury； Venus； Earth； Mars； Jupiter； Saturn； Uranus； Neptune； Pluto）。 It is the first planet unknown to the ancients。 The four outer； Jovian； planets turn out to be very different from the four inner； terrestrial； planets。 Pluto is a separate case。
As the years passed and the quality of astronomical instruments unproved； w