Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site dciem.UUCP Path: utzoo!dciem!ntt From: ntt@dciem.UUCP (Mark Brader) Newsgroups: net.physics,net.astro.expert Subject: Re: pulsing quasars and the like Message-ID: <945@dciem.UUCP> Date: Tue, 5-Jun-84 21:29:34 EDT Article-I.D.: dciem.945 Posted: Tue Jun 5 21:29:34 1984 Date-Received: Tue, 5-Jun-84 22:58:41 EDT References: <2631@ecsvax.UUCP> Organization: NTT Systems Inc., Toronto, Canada Lines: 19 D. Gary Grady (ecsvax!dgary) asks why a large body can't change brightness quickly: ... imagine a spherical body in space light years across. A signal travelling at less than c but consisting of high-frequency pulses travels from the center of the body and reaches the perimeter 'simultaneously' in all directions, causing said perimeter to pulsate in unison. Well, suppose the body is N light years across and its center is M light years from us. For simplicity suppose the south pole of the object points at us. Now a pulse travelling symmetrically from the center of the object causes the entire surface to brighten. Fine. But the light from the south pole takes only N/2+M years to reach us, whereas the light from the equator takes M years, and the light from intermediate south latitudes takes intermediate times. Therefore we see the brightening smeared out over N/2 years. That's why. Mark Brader