Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site rochester.UUCP 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