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Astr111 Photography Projects, Fall 2004

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Uranus, Jody Brown


Uranus is the 7th planet from the sun and the first to be discovered by a telescope. In 1781, William Herschel proved that the orbit of Uranus showed that it is a planet rather than a star or a comet. One year on Uranus is 84 earth years long. Its atmosphere is similar to that of Jupiter and Saturn in that it is made up of mostly hydrogen and helium. About 15 percent of Uranus is hydrogen and helium, 60 percent ice (water, methane, and ammonia), and 25 percent earthy materials (silicates and iron). Uranus' methane-containing atmosphere absorbs red light and reflects blue and green, which gives it a beautiful blue-green color that we see in photographs. The clouds on Uranus are made of ammonia, and are blown in the same direction as the planet's rotation. Uranus rotates on its side, with its axis of rotation almost 90 degrees from its orbital plane. Each pole is thus exposed to sunlight for 42 years, alternately. The planet has five moons that were known before the Voyager 2 mission: Miranda, Ariel, Umbriel, Titania, and Oberon. Ten others were discovered by Voyager 2, and were named after other Shakespearean characters, three of which orbit near the edge of the ring system and help to stabilize Uranus' 11 or so rings. Uranus' magnetic field is very strange. It is tilted 59 degrees from its rotational axis, with the north magnetic pole nearest to the south geographic pole, and the field also does not center on the core of Uranus. Turning once in about 17 hours and 20 minutes, the magnetic field tells us the rotational period of Uranus.

The pictures taken in succession at the Calvin College Observatory show us that Uranus moves relative to the background of stars, and so has an orbit of its own. The size of Uranus can also be calculated from the picture of only Uranus. Its size can be calculated by knowing the size of the total picture in arc seconds and comparing the size of Uranus in the picture to the size of the entire picture. Unfortunately, none of the moons showed up in the photographs. It would have been nice to see the movement of the moons around Uranus over the short period of time the photos were taken. Unfortunately, the moons must have been too dim, despite the fact that they were not all hiding behind the planet at the time.