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Path: utzoo!watmath!clyde!burl!ulysses!allegra!bellcore!decvax!genrad!panda!talcott!harvard!seismo!rochester!sher
From: sher@rochester.UUCP (David Sher)
Newsgroups: net.space,net.physics
Subject: Re:  Re: Light Sails
Message-ID: <6960@rochester.UUCP>
Date: Sat, 2-Mar-85 22:57:57 EST
Article-I.D.: rocheste.6960
Posted: Sat Mar  2 22:57:57 1985
Date-Received: Tue, 5-Mar-85 02:16:09 EST
References: <861@mordor.UUCP>
Reply-To: sher@rochester.UUCP (David Sher)
Followup-To: net.space
Organization: U. of Rochester, CS Dept.
Lines: 15
Keywords: light sails physics
Xref: watmath net.space:3662 net.physics:2199
Summary: 

To you net.physics people this article is a result of a discussion of
light sails and how they work.  The question I am addressing is does
being reflected by a light sail change the wavelength of the reflected
light.  This is a tricky problem because it is not well defined.  
(I am taking this from rememberances of a modern physics class I took
3 years ago so I am not authoritative).   Light only has a wavelength 
relative to an observer. (or a frame I guess).  There was an interesting
problem I was given in the afore mentioned physics class which was
given an observer for which a beam of light with wave length (relative
to the observer) lambda is reflected from a mirror moving with relativistic
velocity v  what is the wave length of the reflected light.  I believe
it is not the same as the original light except when v is a small fraction
of c (whats an epsilon between friends).  Try throwing mirors around and
see for your self :-).  
-David Sher