VARIABLE STARS

Evening Star, Issue 20062, 31 December 1928, Page 11

VARIABLE STARS

I [Written by Mr E. M. Bateson, Director of the Variable Star Section of tlie New Zealand Astronomical Society, for the ‘ Evening Star.’] __ i Even from the earliest times astronomers have noticed that all the stars in the sky are not of constant brightness. Although to the casual observer ail the stars appear the same night after night, with the exception of the change in the times of their rising and setting, there are a number which, to the naked eye, can be seen to change grandally in brightness on closer inspection. > The stars that so change, are called Variable Stars owing to the variability of their light. The first observed star of this class was Algol, which was so named by the Arabs owing to the remarkable changes that this star underwent. The name Algol means “ The Demon.” I Jt is probable that most of the stars are variable, but owing to their vast distance the changes arc. not large enough in most cases to be noticed from the Earth. It is by the study of the Sun that this problem will bo solved, since the Sun is merely an ordinary star, and it is therefore probable that its light undergoes some sort of change. Yearly more aiwl more variable stars are discovered as more accurate equipment is employed. Once a star is found to vary a close track is kept of it. Regular observations are taken from all over the world, and from tlie data derived from these observations it is hoped eventually to be able to interpret the cause of the variations. Jf this can bo done it will go a long way towards solving many of the most outstanding problems in astronomy. As the stars are discovered to vary they are catalogued according to their variations. These groups are given below : Class I.—New stars. Class IT.—Variable stars of long period. Class 111. —Irregular period variables. Class IV.—Short period variables. Class V.—Eclipsing variables of the Algol type. The first class is distinct from the other*, as it is formed by the most wonderful stars that have been observed. Often the stars in this class have reached the third magnitude before they arc discovered, so rapid is their rise in brightness. After attaining a maximum often rivalling Sirius they gradually fade away until once again they become invisible. Many theories have 'been advanced'as to the cause of these sudden outbursts, and these will he dM.lt with in the fol-1 lowing article. The main difference bet won the next three chases is the time occupied by the variables :.i undergoing one complete change of brightness. All those having a period of more than fiftjr days are placed in class two, dthougn this is again sabdiddf-i as the -.•-am iocr.d to present .-.in.clar chaiactvjilsrics. Into ihe next chess are placed tha stars whose" period even cannot be found since their changes are so" krxguUr. The fourth data con-

tut*i tie shorter period yvvjajdes whose vunations sre not caused tij the eclipsing dark body such r.« is the cs>.e with Algol. These isitter eclipsing variables are ’placed in the fifth date. The succeeding arueit-s" wiii deal more fully «ith the onuses of the variations, as well as the methods employed in obsciVing these stars.