"Moonless" Jupiter

None of Planet Jupiter's four bright moons, which ordinarily may be scanned by a $5 or $10 telescope, was visible from the U. S. one evening last week. That was a rare coincidence which had not happened since May 10, 1914 and will not happen again until July 16, 1939.

Jupiter, largest of the Sun's nine planets and heavier than all the other eight planets combined, has nine satellites. Large astronomical telescopes have difficulty in discerning five of them. Two others are each as big as Earth's Moon. The two remaining are each half as large again. They surpass Planet Mercury in size. Names given these four are Callisto, Io, Europa, Ganymede. During last week's performance they rapidly displayed all the relations of satellite to planet.

Ganymede was in occupation, hidden from U. S. view behind Jupiter. Visible were Callisto, Io and Europa. Europa revolved into occultation. Callisto then proceeded into the planetary shadow where it was eclipsed. Only Io then was visible until Ganymede came out from behind Jupiter. Then Io began its transit across the face of Jupiter whose brightness made the duller satellite invisible, and Ganymede passed into the eclipsing shadow. Then all moonless looked nine-mooned Planet Jupiter.

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