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Moon and Antares
On a human scale, the Moon is gigantic. It's more than 2,000 miles in diameter -- about a quarter the size of Earth. And it's a solid chunk of rock, so when you reach the surface, you hit it with a thump.
But on the astronomical scale, the Moon is little more than dust in the solar wind -- a mere speck of matter that hardly registers.
To understand just how tiny, consider its companion tonight: Antares, the brightest star of the constellation Scorpius, the scorpion. The bright orange star stands just to the left of the Moon as night falls.
Antares is one of the giants of the Milky Way galaxy -- it's far bigger, brighter, and heavier than all but a handful of the Milky Way's hundreds of billions of stars.
To get some idea of just how big it is, consider this: If the Moon were the size of a golf ball, Antares would be as wide as all of a golf course's holes laid end to end -- about four miles in diameter.
Unlike the Moon, though, you'd have a tough time knowing just when you arrived at Antares -- there's no solid surface. In fact, the gas at the star's visible surface is so thin that it's barely more than a vacuum. What's more, Antares blows a thick "wind" of gas into space, so there's not a sharp boundary between the star and space itself.
Yet Antares contains so much gas, spread over such a huge volume of space, that the star is one of the brightest in our night sky, even though it's about 550 light-years away.
Script by Damond Benningfield, Copyright 2010