|MadSci Network: Astronomy|
Hi, Why is the sky dark at night? This is at first glance a rather simple question, but it's one that puzzled astronomers for centuries. Edmund Halley (of Halley's Comet fame) worried about it back in the eighteenth century. He wondered why, if we live in an infinite universe with an infinite number of stars, do we not see light from a star no matter where we look? This is now known as "Olbers' Paradox" after the German scientist Heinrich Olbers. Olbers thought that the night sky is dark because some of the stars were hidden by intervening matter (like dust) that blotted out the light from the stars. However, we now know that this just isn't possible. Thermodynamics tells us that the dust would be heated up by the starlight until it glows, so the radiation from the stars would still reach us. The answer actually came from the American poet Edgar Allen Poe. He realized that since there is a limit to how fast light can travel (the speed of light) and that the universe is not infinitely old, the light from the most distant stars just hasn't had enough time to reach us yet. The universe simply isn't old enough to be completely lit up! You can find some more details (including discussion of a few other possible explanations), you could try visting the Olbers' paradox entry in the Usenet Relativity FAQ. Meghan
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