dipper@utastro.UUCP (Debbie Byrd) (10/24/85)
The moons of Uranus helped reveal something interesting about this distant planet. More -- after this. October 24 Three Months to Uranus On today's date in just three more months, the Voyager spacecraft will be closest to the planet Uranus -- the first planet ever discovered with a telescope. Interestingly enough, on today's date in the year 1851, an astronomer named William Lassell discovered two of the moons of Uranus. They were later named Ariel and Umbriel. Uranus itself was discovered in 1781. And two more moons, called Titania and Oberon, also were known by the time Lassell discovered his moons. The two moons found by Lassell and the two previous moons helped reveal something amazing about the planet Uranus. Most moons orbit their parent planets above the planets' equators. Since most planets orbit nearly upright with respect to the plane of the solar system, most moons tend to orbit in that same flat sheet of space around the sun. But the moons of Uranus are different. It was seen early on that they orbit nearly perpendicular to the plane of the solar system -- as if the orbit of Earth's moon were to take it above and below Earth's poles. As it turned out, in the case of Uranus, the moons do orbit more or less above the planet's equator. But Uranus itself is tilted nearly sideways with respect to the plane of the solar system! While the other planet spin nearly upright -- like tops -- Uranus, for part of its orbit at least, rolls along on its side like a ball. The Voyager spacecraft hopefully will get some amazing pictures of this world and its moons when it encounters Uranus -- just three short months from today. Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin