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| Jupiter was first viewed through a telescope in 1610 by Italian philosopher and scientist Galileo Galilei. Until that time, the dominant world view, which was developed by 2nd-century Alexandrian astronomer Ptolemy, held that all of the stars and planets move in orbits around the earth. Galileo, however, observed four satellites, or moons, in orbit around Jupiter. The moons that Galileo saw were collectively named the Galilean moons in honor of their discoverer. When viewed through a modern telescope, the flattened disk of Jupiter has a pearly color with bands of pastel browns and blues. Earth-based observers can best observe Jupiter when it is near solar opposition—that is, when Jupiter is on the side of Earth opposite the sun, or when both planets are aligned with the sun on the same side of the sun. At opposition, the distance from Earth to Jupiter is at its annual minimum, and Jupiter appears as much as one and one-half times larger than it does at other times. Also at opposition, Jupiter rises at sunset and sets at sunrise, which means that it is visible all night long. With the rapid rotation of Jupiter (9.8 hours), it's entire surface can be observed in two days during the long observing periods of opposition. |