MadSci Network: Astronomy

Re: Why is the night sky dark and not fully lit by the light from all the stars

Date: Mon May 15 18:23:13 2000
Posted By: Meghan Gray, Grad student, Astronomy, Cambridge University
Area of science: Astronomy
ID: 958175244.As


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


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