27 July 1992

                                                                Of Mons and Mistresses

        The stereotype of the serious scientist is that of an obsessive-compulsive individual who lets nothing stand in the way of his search for truth. While we know that this stereotype, like all stereotypes, is an oversimplification, it is refreshing to come across scientific writing that shows a sense of humor.
        Some time ago, Carl Sagan of Princeton University related how the moons of Jupiter got their names. Most of us are vaguely aware that the planet Jupiter has more than one moon. Actually, it has 14, four of which were large enough to have been discovered by Galileo, who was using a primitive telescope. These four large moons are referred to as the Galilean satellites.
        The four satellites were "baptized" by a contemporary of Galileo, Simon Marius, who selected the names from classical mythology. "Jupiter especially is charged by the poets with illicit loves," Marius observed. "Especially well known among these are three virgins, whose love Jupiter secretly coveted and obtained , namely Io...Callisto...and Europa." He named the first moon Io; the second, Europa; and the fourth, Callisto.
        Marius gave the name of Ganymede to the third moon, the brightest of the four. He explained, "Even more ardently did he [Jupiter] love the boy Ganymede."
        Marius' "principle" of naming the moons of the planet Jupiter after the illicit loves of the god Jupiter (Zeus) has been followed to the present. Not one of Jupiter's moons has been named after the god's long-suffering wife Juno. The name of Juno, however, has been given to the third asteroid discovered (the first two were named after Ceres and Pallas).
        Apart from retaining the practice of naming Jupiter's moons after his illicit loves, the International Astronomical Union has adopted an additional criterion: the name must end with an a if the moon goes around Jupiter clockwise, but with an e if it moves counterclockwise.
        Thus, for the sixth to the thirteenth Jovian satellites, we have the following names: Himalia, Elara, Pasiphae, Sinope, Lysithea, Carme, Anake and Leda.
        The IAU has not given the 14th moon a name, but this is not because Jupiter had only 13 paramours. He had many others, such as Maia, Alcmene, Leto, Demeter, Semele and Danae -- who are better known than some of the women who have had moons named after them.
        The fifth moon? Well it was discovered in 1892 by E. E. Bernard, who insisted on calling it simply Jupiter V. Soon afterwards, however, the Frenchman Camille Flammario suggested that it be named Amalthea.
        Amalthea is neither a woman nor a man. Amalthea is the goat that suckled the infant Zeus. Sagan wryly commented, "While being suckled by a goat is not precisely an act of illicit love, it must have seemed, to a Gallic astronomer, adequately close."