Whirlwind, a general term for any whirling body of air. The term is most often applied to whirling air created by the swift rising of warm air from near the surface of the earth. Whirlwinds include the "dust devils" that may be seen moving across a field or along a dirt road on a hot day, and the waterspouts of tropical seas.
We take much for granted about our universe, like it's getting bigger. What if the universe stopped expanding and started collapsing inward with a giant crunch?
He is famous for a phrase he never said, for wearing turtlenecks and for hosting the original 'Cosmos' TV series. As enthusiastic about the stars as he was about marijuana, Carl Sagan led a very surprising life. Here are 10 cool facts.