Uranus III 
One of the most beautiful sights in the night sky is an aurora -- a billowing curtain of light high in the atmosphere. But Earth isn't the only planet with aurorae. Two others are in the southeast at dawn right now: Jupiter and Uranus. Jupiter looks like a brilliant star. Much-fainter Uranus is just to its upper left. Through binoculars, it looks like a faint blue-green star.
An aurora flares to life as particles of the solar wind -- funneled by a planet's magnetic field -- strike molecules high in the atmosphere, causing them to glow. On Earth, that glow is mainly in the form of visible light. On Jupiter, it's mainly in the ultraviolet -- a more powerful form of energy. That energy may help heat the top of Jupiter's atmosphere to more than a thousand degrees Fahrenheit.
Uranus also has aurorae, and the top of its atmosphere is also very hot. But the two don't seem to be related -- the planet's aurorae are much less powerful than those on Jupiter.
Instead, ultraviolet radiation from the Sun may be splitting molecules of hydrogen high in the atmosphere, causing them to emit energy that heats other molecules around them. Or daily changes in the Sun's radiation may be causing the planet's atmosphere to pulse in and out, adding energy to the top of the atmosphere.
Texas astronomer Laurence Trafton and others are watching Uranus to try to understand what's heating the fringes of its atmosphere.
More about Uranus tomorrow.
Script by Damond Benningfield, Copyright 2010