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Uranus at Opposition

September 25, 2011

One of the biggest planets in the solar system is putting in its biggest appearance of the year. It lines up opposite the Sun, so it rises around sunset and remains in the sky all night. It’s brightest for the year, too — bright enough to just make out with the unaided eye if you know just where to look and what to look for. But the planet is best seen through binoculars. It looks like a tiny star passing through the constellation Pisces.

Uranus is the solar system’s third-largest planet — four times the diameter of Earth. It looks so tiny because it’s a long way away — almost two billion miles.

For a long time, Uranus was classified as a gas giant — a world similar to Jupiter and Saturn, the only two planets that are bigger. In recent years, though, as they’ve learned more about the interiors of all the outer planets, scientists have come up with a different designation for Uranus and the fourth-largest planet, Neptune: ice giants. While Jupiter and Saturn consist mainly of thick envelopes of hydrogen and helium gas, Uranus and Neptune are made mainly of a slurry of ices — frozen water, methane, and ammonia.

The ices are surrounded by an atmosphere of hydrogen and helium that’s topped by clouds and a haze of methane. The methane absorbs red wavelengths of light, giving Uranus an overall greenish color. That color is visible through telescopes, and may even show up in binoculars, as you take in the big planet’s big show.


Script by Damond Benningfield, Copyright 2011


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