dipper@utastro.UUCP (Debbie Byrd) (01/12/85)
There's something very special about the speed of light -- and we'll tell you what that is -- right after this. January 12: The Speed of Light Light travels at a speed of 186 thousand miles per second. That speed is special, because it measures the same for everyone -- no matter how fast you move relative to it. To see how strange that is, consider things moving at more ordinary speeds. Say you're standing still, and a car comes toward you at 60 miles per hour. Then suppose you get in a second car, and drive toward the first at 30 miles per hour. The first car now seems to come at you at 90 miles per hour, relative to your car. But light speed doesn't work like that. Light is never seen by any observer to speed up or slow down, no matter how fast he moves with respect to the light. Imagine the two cars again, only this time say the first car is a light beam, and the second an ultra-fast rocketship. The light beam shoots toward you at light speed, naturally, 186 thousand miles per second. You now blast off toward it at very high speed, say half the speed of light. You'd expect the light beam to seem faster than it was before, relative to your rocket -- but it won't. No matter how fast you go, you will still see the light coming at you at 186 thousand miles per second. Weird as it sounds, the constancy of the speed of light has been verified in many experiments, and is one of the foundations of Einstein's theory of relativity. Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin