From: utzoo!decvax!cca!LRC.Slocum@UTEXAS-20@sri-unix Newsgroups: net.space Title: red-shift & distance measurement Article-I.D.: sri-unix.2580 Posted: Mon Aug 9 13:52:02 1982 Received: Tue Aug 10 03:44:57 1982 From: Jonathan SlocumUsing red-shift to compute distance does not work within the Local Group (= Milky Way, Andromeda, Magellanic Clouds, etc.) -- in other words, not anywhere close to here -- because these galaxies are gravitationally bound, pursuing orbits around a common center, and hence are not expanding in the sense defined by Hubble. Cepheid variables (whose intrinsic luminosities are mathematically related to their periods of variation) are used to calculate distances in these ranges. The discovery that there are two different types (technically, "populations") of Cepheid variables is what led to the revision of the "measured" distance to Andromeda, among others, some years ago. -------