Peering into the past

I was reading Jack McDevitt’s excellent Infinity Beach several days ago, and ran across a really neat idea. He said it in passing, and I had to re-read the passage at least ten times before I grasped the awesomeness of it.

Ok, so we know that light travels at a certain speed (2.998 X 10^8 m/s in a vacuum). There are stars in the heavens that we see every night, stars that are actually dead. They’ve burned out, but they are so far away we’re seeing the light that was emitted from them hundreds of years ago. It’s neat.

What I never really thought about is that the opposite is true. Alpha Centauri is a star that is 4.37 light-years away. So the pinprick of light we see as the star, actually left on its journey 4.37 years ago.

Here is the kicker. If I was in a starship orbiting Alpha Centauri, and turned my powerful optical telescope to see my home planet of earth, I would be seeing 4.37 years IN THE PAST. That is, the image of earth I’d be seeing actually left earth 4.37 years ago. In a sense, it’s looking backward in time.

Think of the implications of this. I have a starship, and I travel to a point 515 light-years away, I could stop, train my telescope to earth, look out on the Atlantic ocean and witness the voyage of Columbus discovering the New World. (2007 - 515 = 1492)

In the future, will historians make travels to far off places, to specifically take advantage of this trait of light?