Brightness of Stars.

Kaipara and Waitemata Echo, 14 August 1914, Page 2

Brightness of Stars.

ITS CAUSE. The distances of fixen stnrs were first measured about 1840, when Bessel found a parallax of I-3rd second for 61 Cygni, and Henderson one of about 1 second (afterwards corrected to ;J second), for Alpha Centauri. A parallax of one second corresponds to a distance of n>,2<K>,ooo million miles. or ;•> light years. .Reviewing the progress to the present time, Mr. Lawrence llichardson, in a late lecture, mentions that the best recent parallax determinations have been obtained by photographing stars to show their apparent changes of position as compared with stars much beyond them in nearly the same line, and in this work the Yerkes telescope has excelled, with an average probable error of only an eightieth of a second, or about one 20,UO0th of an inch on the photographic plate. Direct parallax is fairly reliable of about f>o light years, within which distance there are probably I.ikh) stars. The fewness of near bright stars indicates

that some stars have great intrinsic brightness instead of being made brilliant by nearness alone, and the same reasoning implies that faint stars are not so distant as their faint-ness suggests. The more uniform proper motion is a more accurate guide to distance than brightness. Fair estimates of the distance of groups of stars have been made from the proper motion, with the motion in the line. of sight shown by the spectroscope, and an average of 534 light years has been found for a group of 312 helium stars. BYom the convergence due to parallel motion, f> of the 7 stars of the (Jreat Bear have been showa to be from 69 to 78 light years distant. Speculations as to the distance' of the most remote stars vary from millions of light years down to '2,000 or 3,000.