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From: mercury@ut-ngp.UUCP (Larry E. Baker)
Newsgroups: net.space
Subject: Re: Speed Of Light
Message-ID: <1712@ut-ngp.UUCP>
Date: Thu, 9-May-85 11:45:10 EDT
Article-I.D.: ut-ngp.1712
Posted: Thu May  9 11:45:10 1985
Date-Received: Sat, 11-May-85 08:13:24 EDT
References: <2073@decwrl.UUCP>
Organization: University of Texas at Austin
Lines: 37

[]


> Hence, BOTH lasers are going at 1.0C, but RELATIVE TO DIFFERENT BASES.
> When both lasers get to Ship #1, won't the laser from Earth have an
> apparent speed of .9C (C minus the speed of Ship #1 (.1C)), and won't
> the laser from Ship #2 have an apparent speed of 1.8C (.9C Ship #2
> velocity plus 1.0C speed of laser minus 0.1C velocity of Ship #1)? 

The light from ship 2 will simply shift to a higher frequency.  This
is known as the Doppler effect.  You can see the same thing happen
with cars and trains -- when a car drives by at 60 miles per hour
blowing its horn, the tone changes as it pass you.  This is due to the
compression of the sound waves as the car is approaching, and the
expansion of the waves as the car departs.

The same is true for light.  Were you a stationary observer in front
(hopefully not directly in front) of ship 2, then you would see laser
light of a much higher frequency as the ship is nearing you, and after
it passed (assuming you're still alive), were it to shine the laser
BACKWARDS, you would see laser light of a much lower frequency.

If the light were 'white' light, then, as the ship approaches, it
would shift to the blue end of the spectrum. (ultraviolet shifting out
of the visible spectrum, most of the other colors also, and infrared
shifting down into the visible spectrum).  As the ship departs, you
would see 'red' light as the infrared shifts DOWN out of the visible
spectrum and ultraviolet shifts down into blue.

This rather shakey explination probably has holes big enough to peg
rocks through, as it is based on Physics that I learned long ago, but
I hope it helps.

-- 
-  Larry Baker @ The University of Texas at Austin
-  ... {seismo!ut-sally | decvax!allegra | tektronix!ihnp4}!ut-ngp!mercury
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