Saturday, March 6, 2010

The Astonishing Night Sky

"Oh," says the pretty brunette in the sweater curling up against her boyfriend in the convertible at Lookout Point, "Isn't the sky so beautiful! Reality is so much better than television!"

Assuming that he is checking-out the stars and not her, he will probably agree.

But, in a sense, they would both be wrong.

In a sense, when you look up at the night sky, what you see up there is not reality.

Virtually every single star you see up there is not quite where you see it. Some of the stars are in positions radically different than where you see them. A few of the stars seen by us in the sky occasionally have actually ceased to exist as stars.

When you look at the night sky, you are looking at the past.

And not just "the past," but a collection of different pasts.

Alpha Centauri, the closest star, is about 4.2 light years awy. When we look at it in the night sky, we are looking at where the star was 4.2 years ago.

When we look at Sirius, we are looking at where that star was 8.5 years ago.

When we look at the star called Groombridge 1618, we are looking at where that star was 15.8 years ago.

When we look at Betelgeuse near the constellation Orion, we are looking at where that giant star was 640 years ago.

The really interesting thing about Betelgeuse is that it is one of those stars which in fact may no longer exist, even though we can see it! When we aim our telescopes at Betelgeuse and look at its 640 year old light, changes in the light suggest that Betelgeuse was shrinking 640 years ago, and that it may have already collapsed in upon itself with that giant BANG known as a supernova, blasting much of the material which used to be the star out into space, leaving only a tiny remnant. We just don't know that yet because the light of the self-destroying blast just has not reached us, yet.

So, when you look at the stars in the vicinity of Orion's Belt, you may well be looking at a star which isn't even up there anymore!

Andromeda Galaxy is a radically different problem. It is the only spiral galaxy outside of our own visible to the naked eye on a clear night. When we look at it, we are looking at it as it was and where it was...when? Answer: 2,500,000 years ago!

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