Andromeda Galaxy

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The phrase "as far as the eye can see" takes on an entirely new meaning when you gaze into the night sky. Instead of miles and miles, you can see millions of miles -- and sometimes a whole lot farther.

In fact, the most-distant object that's readily visible to the unaided eye soars high overhead this evening: the Andromeda galaxy.

It's not much to look at -- just a faint smudge of light, like a tiny puff of cloud. But it looks insignificant only because of its great distance -- around two and a half million light-years.

In truth, Andromeda is anything but insignificant. Like our own galaxy, the Milky Way, it's home to hundreds of billions of stars. It's a wide, flat disk, with its brightest stars tracing out spiral arms. The brightest portion of the disk is perhaps 125,000 light-years across -- a little bigger than the Milky Way.

Because of its distance, the light we see from Andromeda tonight actually left the galaxy about two and a half million years ago. But the galaxy's disk is tilted as seen from Earth, so the far edge is a lot farther than the near edge. So even though we can see the entire galaxy at a single glance, we're not seeing it as it looked at one instant in time. Instead, light from the far edge is tens of thousands of years older than light from the near edge. So in both time and distance, the edge of the Andromeda galaxy really is as far as the eye can see.

More about Andromeda tomorrow.

Script by Damond Benningfield, Copyright 2008

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