February 07, 2002
Intergalactic Perspective

Just about everyone has heard of the term "light year", and (hopefully) everyone knows in at least a vague sense what it means. But I know that I, for one, didn't know what that really means for a very long time.

Think of it this way. Lets say you have one of those funky little laser light things, the kind you hang on your keychain and drive the cats bonkers with. If you go outside, point it straight up, turn it on, and start counting seconds, the light that comes out of it travels 186,000 miles by the time you say "one-onethousand".

Now, that's a pretty big number. Big enough that it's hard to get your head around all by itself, but it's important to understand just exactly how far 186,000 miles is for the rest of this to work. So, two examples:

  • A dollar bill is about 6 inches long (I think... Ellen took all my money and I'm kind of working from memory). 186,000 one dollar bills stuck end-to-end strech almost 18 miles.
  • If you got in an airplane and flew west for 186,000 miles, you would go around the entire planet not quite 8 times.

So, to repeat, that little laser's light is so fast that if you could curve it (you can't, at least not easily), it would go around the world not quite 8 times in one second. BeebeepzipBANG! indeed.

Ok, now to you and me that seems like a damn far distance, but it's not, at least not on the scales we're talking about. For example, the moon is so far away that when the astronauts were talking to us it took just a little more than a second for the signal to reach us. Sort of like talking to someone on a bad international phone line. But this is just the closest planetary body the earth has.

The sun is the closest star to the earth. It averages to be about 93,000,000 miles away from us (the earth's orbit is eliptical, so the values change a bit). Lets say you happen to be standing in the middle of the New Mexico desert when you're flashing your laser beam into the sky, so of course some aliens swoop down, abduct you, and take you to their specially-made prison near the surface of the sun. While sitting in your cell trying to figure out if the chrome plated lawnmower in the corner is the toilet or your bed, you try to blink a distress signal to earth using a big honking version of your laser light thingy the aliens gave you when they tossed you in here (snickering while they did so). The sun is so far away from the earth it takes that (now supercharged) beam of light, that same beam that can go around our whole planet nearly eight times in a second, 8 whole minutes to get to the earth. And it would take that long for you to see us signal back "you're screwed". The entire message exchange, from start to finish, would take longer than half of a Friends rerun (and we know how important those are). And the kicker is that's the closest star we got.

The next closest star is actually a pair of stars, Alpha Centauri A and Alpha Centauri B. Lets say these aliens get tired of you complaining about canned ravioli every night and so ship you off to an orbiting lab around Alpha Centauri A. If you were to signal with your laser from there, the beam of light that goes 8 times around the planet in a second takes a whopping four and a half years (hence "light years") to get to earth. But it gets better.

The earth is on one edge of a bar-spiral galaxy containing, as Mr. Carl Sagan (formerly living proof that pot doesn't always make you stupid) liked to say, billions of stars. Lets say you got confused and instead of pointing at earth you pointed your light at the other side of the galaxy. It would take about 175,000 years for that beam of light, the same beam of light that reaches the earth from the sun in just a few minutes, to reach some ammonia-breathing amateur astronomer ("send clean underwear" being the way you choose introduce yourself to such a creature). But it gets better than that.

The next nearest spiral galaxy to ours is the Andromeda galaxy. It lies three and a half million light years away. The closest thing to humans that lived on our planet at that point were some short, hairy, sad little bipeds that were literally still swinging from the trees. And we're not done yet.

our galaxy contains billions of stars, but our universe contains billions of galaxies, each one with at least as many stars. The most distant galaxy we've been able to find so far is 8 billion light years away, a time span roughly twice the age of our planet. It is estimated that the universe itself, the leading edge of the big bang, is about 4 billion years beyond that.

So the next time someone sits too close to you at a theater, have some fun thinking just how far away they could go if you really wanted them to "get lost".

Posted by scott at February 07, 2002 04:32 PM

eMail this entry!

man scott, you talk a lot.


Posted by: melbernai on February 7, 2002 06:05 PM

Tell other folks! We need traffic! Crosslink crosslink crosslink! :)

Posted by: scott on February 8, 2002 08:12 PM

don't worry, i have it linked on my diary .... and, i got a link to my diary from your diary, so someone must be reading it. unless that was you :P~


Posted by: melbernai on February 9, 2002 10:27 AM
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