by Isaac Asimov
Then there -is a reddish planet and red is obviously the color of blood; that is, of war and conflict. The Baby lonians named this planet "Nergal" after their god of war, and the Greeks again followed suit by naming it "Ares" after theirs. Astronomers who study the surface features of the planet are therefore studying "areography." The Latins used their god of war, Mars, for the planet. The genitive form is Martis, so we can speak of the "Martian canals."
The planet nearest the Sun, appears, like Venus, as both an evening star and morning star. Being smaller and less reflective than Venus, as well as closer to the Sun, it is much harder to see. By the time the Greeks got around to naming it, the mythological notion had taken hold. The evening star manifestation was named "Hermes," and the morning star one "Apollo."
The latter name is obvious enough, since the later Greeks associated Apollo with the Sun, and by the time the planet Apollo was in the sky the Sun was due very shortly. Because the planet was closer to the Sun than any other planet (though, of course, the Greeks did not know this was the reason), it moved more quickly against the stars than any object but the Moon. This made it resemble the wing-footed messenger of the gods, Hermes.
But giving the planet two names was a matter of conserv atism. With the Venus matter straightened out, Hermes/Apollo was quickly reduced to a single planet and Apollo was dropped. The Romans named it "Mercurius," which was their equivalent of Hermes, and we call it Mercury.
The quick journey of Mercury across the stars is like the lively behavior of droplets of quicksilver, which came to be called "mercury," too, and we know the type of personality that is described as "mercurial."
There is one planet left. This is the most slowly moving of all the planets known to the ancient Greeks (being the farthest from the Sun) and so they gave it the name of an ancient god, one who would be "pected to move in grave, and solemn steps. They called it "Cronos," the father of Zeus and ruler of the universe before the suc cessful revolt of the Olympians under Zeus's leadership.
The Romans gave it the name of a god they considered the equivalent of Cronos and called it "Saturnus," which to us is Saturn. People born under Saturn are supposed to reflect its gravity and are "satumine."
For two thousand years the Earth, Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn remained the only known bodies of the Solar System. Then came 1610 and the Italian astronomer Galileo Galilei, who built himself a telescope and turned it on the heavens. In no time at all he found four subsidiary objects circling the planet Jupiter.
(The German astronomer Johann Kepler promptly named such subsidiary bodies "satellites," from a Latin word for the hangers-on of some powerful man.)
There was a question as to what to name the new bodies.
The mythological names of the planets had hung on into the Christian era, but I imagine there must have been some natural hesitation about using heathen gods for new bodies.
Galileo himself felt it wise to honor Cosimo Medici H, Grand Duke of Tuscany from whom he expected (and later received) a position, and called them Sidera MetUcea (the Medicean stars). Fortunately this didn't stick. Nowa days we call the four satellites the "Galilean satellites" as a group, but individually we use mythological names after all. A German astronomer, Simon Marius, gave them these names after having discovered the satellites one day later than Galileo.
The names are all in honor of Jupiter's (Zeus's) loves, of which there were many. Working outward from Jupiter, the first is lo (two syllables please, eye'oh), a maiden whom Zeus turned into a heifer to hide her from his wife's jealousy. The second is Europa, whom Zeus in the form of a bull abducted from the coast of Phoenicia in Asia and carried to Crete (which is how Europe received its name).
The third is Ganymede, a young Trojan lad (well, the Greeks were liberal about such things) whom Zeus ab ducted by assuming the guise of an eagle. And the fourth is Callisto, a nymph whom Zeus's wife caught and turned into a bear.
As it happens, naming the third satellite for a male rather than for a female turned out to be appropriate, for Ganymede is the largest of the Galilean satellites and, indeed, is the largest of any satellite in the Solar System.
(It is even larger than Mercury, the smallest planet.)
The naming of the Galilean satellites established once and for all the convention that bodies of the Solar System were to be named mythologically, and except in highly unusual instances this custom has been followed since.
In 1655 the Dutch astronomer Christian Huygens dis covered a satellite of Saturn (now known to be the sixth from the planet). He named it Titan. In a way this was appropriate, for Saturn (Cronos) and his brothers and sisters, who ruled the Universe before Zeus took over, were referred to collectively as "Titans." However, since the name refcrs to a group of beings and not to an indi vidual being, its use is unfortunate. The name was ap propriate in a second fashion, too. "Titan" has come to mean "giant" because the Titans and their allies were pictured by the Greeks as- being of superhuman size (whence the word "titanic"), and it turned out that Titan was one of the largest satellites in the Solar System.
The Italian-French astronomer Gian Domenico Cassini was a little more precise than Huygens had been. Between 1671 and 1684 he discovered four more satellites of Saturn, and these he named after individual Titans and Titanesses.
The satellites now known to be 3rd, 4th, and 5th from Saturn he named Tethys, Dione, and Rhea, after three sisters of Saturn. Rhea was Saturn's wife as well. The 8th satellite from Saturn he named Iapetus after one of Satum's brothers. (Iapetus is frequently mispronounced.
In English it is "eye-ap'ih-tus.") Here finally the Greek names were used, chiefly because there were no Latin equivalents, except for Rhea. There the Latin equivalent is Ops. Cassini tried to lump the four satellites he had discovered under the name of "Ludovici" after his patron, Louis XIV-Ludovicus, in Latin-but that second at tempt to honor royalty also failed.
And so within 75 years after the discovery of the tele scope, nine new bodies of the Solar System were discovered, four satellites of Jupiter and five of Saturn. Then some thing more exciting turned up.
On March 13, 1781, a German-English astronomer, William Herschel, surveying the heavens, found what he thought was a comet. This, however, proved quickly to be no comet at all, but a new planet with an orbit outside that of Saturn.
There arose a serious problem as to what to name the new planet, the first to be discovered in historic times.
Herschel himself called it "Georgium Sidus" ("George's star") after his patron, George III of England, but this third attempt to honor royalty failed. Many astronomers felt it should be named for the discoverer and called it "Herschel." Mythology, however, won out.
The German astronomer Johann Bode came up with a truly classical suggestion. He felt the planets ought to make a heavenly family. The three innermost planets (exclud ing the Earth) were Mercury, Venus, and Mars, who were siblings, and children of Jupiter, whose orbit lay outside theirs. Jupiter in turn was the son of Saturn, whose orbit lay outside his. Since the new planet had an orbit outside Satum's, why not name it for Uranus, god of the sky and father of Saturn? The suggestion was accepted and Uranus* it was. What's more, in 1798 a German chemist, Martin Heinrich Klaproth, discovered a new element he named in its honor as "uranium."
In 1787 Herschel went on to discover Uranus's two largest satellites (the 4th and 5th from the planet, we now know). He named them from mythology, but not from Graeco-Roman mythology. Perhaps, as a naturalized Englishman, he felt 200 per cent English (it's that way, sometimes) so he turned to English folktales and named the satellites Titania and Oberon, after the queen and king of the fairies (who make an appearance, notably, in Shakespeare's A Midsummer Night's Dream).
In 1789 be went on to discover two more satellites of Saturn (the two closest to the planet) and here too he disrupted mythological logic. The planet and the five satellites then known were all named for various Titans and Titanesses (plus the collective name, Titan). Hersche
l named his two Mimas and Enceladus (en-seYa-dus) after * Uranus is pronounced "yooruh-nus." I spent almost all my life accenting the second syllable and no one ever corrected me. I just happened to be reading Webster's Unabridged one day… two of the giants who rose in rebellion against Zeus long after the defeat of the Titans.
After the discovery of Uranus, astronomers climbed hungrily upon the discover-a-planet bandwagon and searched particularly in the unusually large gap between Mars and Jupiter. The first to find a body there was the Italian astronomer Giuseppe Piaz2i. From his observatory at Palermo, Sicily he made his first sighting on January 1, 1801.
Although a priest, he adhered to the mythological con vention and named the new body Ceres, after the tutelary goddess of his native Sicily. She was a sister of Jupiter and the goddess of grain (hence "cereal") and agriculture.
This was the second planet to receive a feminine name (Venus was the first, of course) and it set a fashion. Ceres turned out to be a small body (485 miles in diameter), and many more were found in the -gap between Mars and Jupiter. For a hundred years, all the bodies so discovered were given feminine names.
Three "planetoids" were discovered in addition to Ceres over the next six years. Two were named Juno and Vesta after Ceres' two sisters. They were also the sisters of Jupiter, of course, and Juno was his wife as well. The remaining planetoid was named Pallas, one of the alternate names for Athena, daughter of Zeus (Jupiter) and there fore a niece of Ceres. (Two chemical elements discovered in that decade were named "ceriunf' and "paradiunf' after Ceres and Pallas.)
Later planetoids were named after a variety of minor goddesses, such. as Hebe, the cupbearer of the gods, Iris, their messenger, the various Muses, Graces, Horae, nymphs, and so on. Eventually the list was pretty well exhausted and planetoids began to receive trivial and foolish names. We won't bother with those.
New excitement came in 1846. The motions of Uranus were slightly erratic, and from them the Frenchman Urbain J. J. Leverrier and the Englishman John Couch Adams calculated the position of a planet beyond Uranus, the grav 72 itational attraction of which would account for Uranus's anomalous motion. The planet was discovered in that position.
Once again there was difficulty in the naniing. Bode's mythological family concept could not be carried on, for Uranus was the first god to come out of chaos and had no father. Some suggested the planet be named for Leverrier.
Wiser council prevailed. The new planet, rather greenish in its appearance, was named Neptune after the god of the sea.
(Leverrier also calculated the possible existence of a' planet inside the orbit of Mercury and named it Vulcan, after the god of fire and the forge, a natural reference to the planet's closeness to the central fire of the Solar System. However, such a planet was never discovered and undoubtedly does not exist.)
As soon as Neptune was- discovered, the English astron omer William Lassell turned his telescope upon it and dis covered a large satellite which he named Triton, ap propriately enough, since Triton was a demigod of the sea and a son of Neptune (Poseidon).
In 1851 Lassell discovered two more satellites of Uranus, closer to the planet than Herschel's Oberon and Titania. Lassell, also English, decided to continue Her schel's English folklore bit. He turned to Alexander Pope's The Rape of the Lock, wherein were two elfish characters, Ariel and Umbriel, and these names were given to the satellites.
More satellites were turning up. Saturn was already known to have seven satellites, and in 1848 the American astronomer George P. Bond discovered an eighth; in 1898 the American astronomer William H. Pickering discovered a ninth and completed the list. These were named Hy perion and Phoebe after a Titan and Titaness. Pickering also thought he had discovered a tenth in 1905, and named it Themis, after another Titaness, but this proved to be mistaken.
In 1877 the American astronomer Asaph Hall, waiting for an unusually close approach of Mars, studied its sur 73 roundings carefully and discovered two tiny satellites, which he named Phobos ("fear") and Deimos ("teffor"), two sons of Mars (Ares) in Greek legend, though obvi ously mere personifications of the inevitable consequences of Mars's pastime of war.
In 1892 another American astronomer, Edward E.
Barnard, discovered a fifth satellite of Jupiter, closer than the Galilean satellites. For a long time it received no name, being called "Jupiter V" (the fifth to be discovered) or "Barnard's satellite." Mythologically, however, it was given the name Amalthea by the French astronomer Camille Flammarion, and this is coming into more com mon use. I am glad of this. Amalthea was the nurse of Jupiter (Zeus) in his infancy, and it is pleasant to have the nurse of his childhood closer to him than the various girl and boy friends of his maturer years.
In the twentieth dentury,no less than seven more Jovian satellites were discovered, all far out, all quite small, all probably captured planetoids, all nameless. Unofficial names have been proposed. Of these, the three planetoids nearest Jupiter bear the names Hestia, Hera, and Demeter, after the Greek names of the three sisters of Jupiter (Zeus).
Hera, of course, is his wife as well. Undeithe Roman versions of the names (Vesta, Juno, and Ceres, respec tively) all three are planetoids. The two farthest are Posei don and Hades, the two brothers of Jupiter (Zeus). The Roman version of Poseidon's name (Neptune) is applied to a planet. Of the remaining satellites, one is Pan, a grandson of Jupiter (Zeus), and the other is Adrastea, another of the nurses of his infancy.
The name of Jupitees (Zeus's) wife, Hera, is thus applied to a satellite much farther and smaller than those commemorating four of his extracurricular affairs. I'm not sure that this is right, but I imagine astronomers under stand these things better than I do.
In 1898 the German astronomer G. Witt discovered an unusual planetoid, one with an orbit that lay closer to the Sun than did any other of the then-known planetoids. It inched past Mars and came rather close to Earth's orbit.
Not counting the Earth, this planetoid might be viewed as passing between Mars and Venus and therefore Witt gave it the name of Eros, the god of love, and the son of Mars (Ares) and Venus (Aphrodite).
This started a new convention, that of giving planetoids with odd orbits masculine names. For instance, the planet oids that circle in Jupiter's orbit all received the names of masculine participants in the Trojan war: Achilles, Hector, Patroclus, Ajax, Diomedes, Agamemnon, Priamus, Nestor, Odysseus, Antilochus, Aeneas, Anchises, and Troilus.
A particularly interesting case arose in 1948, when the German-American astronomer Walter Baade discovered a planetoid that penetrated more closely to the Sun than even Mercury did. He named it Icarus, after the mythical character who flew too close to the Sun, so that the wax holding the feathers of his artificial wings melted, with the result that be fell to his death.
Two last satellites were discovered. In 1948 a Dutch American astronomer, Gerard P. Kuiper, discovered an innermost satellite of Uranus. Since Axiel (the next inner most) is a character in William Shakespeare's The Tem pest as well as in Pope's The Rape of the Lock, free asso ciation led Kuiper to the heroine of The Tempest and he named the new satellite Miranda.
In 1950 be discovered a second satellite of Neptune.
The first satellite, Triton, represents not only the name of a particular demigod, but of a whole class of merman-like demigods of the sea. Kuiper named the second, then, after a whole class of mermaid-like nymphs of the sea, Nereid.
Meanwhile, during the first decades of the twentieth century, the American astronomer Percival Lowell was searching for a ninth planet beyond Neptune. He died in 1916 without having succeeded but in 1930, from his ob servatory and in his spirit, Clyde W. Tombaugh made the discovery.
The new planet was named Pluto, after the god of the Underworld, as was appropriate since it was the planet farthest removed from the light of the Sun. (And in 1940, when two elements were found beyond uranium, they were named "neptunium!' and "plutonium" after Neptune and Pluto, the two planets beyond Uranus.)
Notice, though, that the f
irst two letters of "Pluto,' are the initials of Percival Lowell. And so, ft0y, an astron omer got his name attached to a planet. Where Herschel and Leverrier had failed, Percival Lowell had succeeded, at least by initial, and under cover of the mythological conventions.
6. Round And Round And…
Any-one who writes a book on astronomy for the general public eventually comes up against the problem of trying to explain that the Moon always presents one face to the earth, but is nevertheless rotating.
To the average reader who has not come up against this problem before and who is inpatient with involved subtleties, this is a clear contradiction in terms. It is easy to accept the fact that the Moon always presents one face to the Earth because even to the naked eye, the shadowy blotches on the MooWs surface are always found in the same position. But in that case it seems clear that the Moon is not rotating, for if it were rotating we would, bit by bit, see every portion of its surface.
Now it is no use sm.Uing gently at the lack of sophistica tion of the average reader, because he happens to be right.
The Moon is not rotating with respect to the observer on the Earth's surface. When the astronomer says that the Moon is rotating, he means with respect to other observers altogether.
For instance, if one watches the Moon over a period of time, one can see that the line marking off the sunlight from the shadow progresses steadily around the Moon; the Sun shines on every portion of the Moon in steady pro gression. This means that to an observer on the surface of the Sun (and there are very few of those), the Moon would seem to be rotating, for the observer would, little by little'see every portion of the Moon's surface as it turned to be exposed to the suiidight.
