dipper@utastro.UUCP (Debbie Byrd) (06/27/85)
Earth isn't the only planet in the solar system with a blue sky. More -- in a moment. June 27 Blue Skies Unless you look near the sun, the sky seen from space appears black. But on Earth the daytime sky appears very bright. Some of the rays of sunlight that would miss us in space get scattered overhead by Earth's atmosphere. The atmosphere also makes the sky blue -- it scatters blue light much more than red light. At least two other worlds in the solar system may also have blue skies. Both of these worlds are surrounded by clouds -- so, like an airplane passenger who takes off on an overcast day on Earth, you'd have to get above the clouds to see the blue skies. Above the multi-colored cloud bands of the largest planet Jupiter, the sky appears blue for the same reason that Earth's sky does. The atmosphere above Jupiter's clouds has about the same pressure as near Earth's surface -- and scatters sunlight in the same way. A visiting Earthling wouldn't want to breathe Jupiter's air. It's poisonous -- mostly hydrogen and a little helium -- with ammonia, methane and carbon dioxide mixed in. But above Jupiter's swirling cloudtops, you'd see a blue sky -- in which the sun would appear only about one-fifth the size of the sun as seen from Earth. Another world with blue skies is Titan, Saturn's largest moon. Titan's surface is constantly shrouded in a thick blanket of orange smog. This moon's atmosphere -- also unbreatheable by humans -- contains mostly nitrogen and methane. But above Titan's smoggy clouds would be a blue sky -- dominated by the sight of the nearby planet with a thousand rings -- Saturn. Script by Diana Hadley. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin