396 THE POPULAR SCIENCE MONTHLY. 



"NEW" AND VARIABLE STARS. 



Br J. ELLAED GOEE. 



TO ordinary observation the light of the stars seems to be con- 

 stant. Although of various degrees of brilliancy, the bright- 

 ness of each individual star appears to most people to be invari- 

 able. This is, of course, true with reference to the great majority 

 of the stars which deck our midnight sky. There are, however, 

 many objects the light of which is subject to considerable fluctu- 

 ations. These are known as variable stars, and form one of the 

 most interesting classes of objects visible in the stellar heavens. 

 Over two hundred are now known to be certainly variable in 

 light, and many others have been suspected of inconstancy. In 

 some of these stars the changes of brightness can only be detected 

 by careful watching, but in many the light is variable to a consid- 

 erable extent. In the variable star Chi Cygni, for example, the 

 star's light at maximum is about sixteen hundred times the light 

 at minimum. At its brightest it is sometimes fairly visible to the 

 naked eye, whereas in its faintest phase a pretty good telescope is 

 required to see it at all. 



These most interesting and mysterious objects have been 

 divided into different classes, according to the character of the 

 light- variation and the length of the period which completes the 

 cycle of their curious changes. The classification now generally 

 adopted is that proposed by Prof. Pickering, of the Harvard Ob- 

 servatory, U. S. A. This includes five classes, which are as fol- 

 lows : 1. Temporary or " new stars " ; 2. Stars with regular peri- 

 ods of considerable length ; 3. Irregular variables, having no defi- 

 nite period ; 4. Variables of short period say, under thirty days ; 

 and, 5. Variables of the type of Algol, or those which, at regular 

 intervals, undergo a sudden (or comparatively sudden) diminu- 

 tion of brightness lasting for a few hours only, the star remaining 

 constant in light (or nearly so) during the remainder of its period. 

 A short account of these different classes may prove of interest to 

 the general reader. 



1. " Temporary " or " new stars " are perhaps the rarest phe- 

 nomena visible in the heavens. Comets at least, those visible to 

 the naked eye are rare celestial visitors. Telescopic comets are, 

 however, tolerably numerous, and scarcely a year passes without 

 the discovery of several of these faint objects. Very few " new 

 stars " have, however, been recorded in the annals of astronomical 

 history. I refer, of course, to those which can properly be termed 

 " new " that is, stars the existence of which was previously un- 

 known to astronomers, and which, blazing out suddenly, remained 

 visible for a short time, and then faded away without again obtain- 



