THE NOMENCLATURE OF VARIABLE STARS. 



By F. A BELLAMY, M.A., F.R.A.S. 



The present state of chaos in the nomenclature used 

 for variable stars — and it is daily increasing — calls for 

 careful consideration by astronomers to remove some 

 of the present anomalies, and, in view of the immense 

 increase in the number of known variable stars — 

 which will be still further increased by photographic 

 means — to establish some definite, convenient, 

 intelligible, and permanent notation. 



The beginning of astronomical observations of the 

 variability in the light of stars may be placed in the 

 year 1572 with the discovery of the star which is 

 usually known as Tycho Brahe's Nova in the constel- 

 lation of Cassiopeia, or sometimes as B Cassiopeiae. 

 In the next hundred years three more such stars 

 (Novae) were discovered in 1600, 1604, and 1670, 

 and are known as P Cygni, a star in Serpentis, and 

 11 Vulpeculae. Until about one hundred years ago 

 not many observations of the variability in the light 

 of stars, or of Novae, are recorded. Systematic and 

 careful estimations of the magnitudes of certain 

 stars were made about seventy-five years ago, chiefly 

 by Schmidt (of Athens), Argelander (of Bonn), Heis, 

 and, later, by Hind, Pogson and J. Baxendell in 

 this country : their observations soon proved the 

 degree of variation of light in a number of stars they 

 had kept under frequent observation ; and, incident- 

 ally, these observers — to be more precise Argelander 

 and Pogson — laid the basis of the scale for accurate 

 stellar magnitudes, and afforded us both the means 

 of determining relative magnitudes and of carrying 

 on a magnitude scale with a definite light-ratio. 

 One may say quite fairly that for the last seventy 

 years all visual estimations of stellar magnitudes have 

 been made on this basis (Argelander and Pogson) 

 without change, and Pogson's value of the light- 

 ratio, or difference in the star's light from one 

 magnitude to the next, of 2 • 5 12, or logarithm ■ 400, 

 has since been universally adopted, though Professor 

 E. C. Pickering's latest photometric work indicates 

 a slightly different value ; also he proves that 

 Argelander's magnitudes of the fainter stars observed, 

 8-0 to 9-5 magnitude, require diminishing by some 

 tenths of a magnitude : this is probably due to the 

 small size of Argelander's telescope, which is still 

 in situ at Bonn as when last used by Argelander 

 and Schonfeld. This by way of a parenthesis to 

 indicate the origin of accurate stellar magnitudes ; 

 for, without a uniform basis, the observations upon 

 variable stars for the determination of their periods 

 would be useless. 



Returning to the definite subject of this note, the 

 first catalogue of variable stars appears to have been 



that formed and published by Argelander in 1844, 

 and was published in Schumacher's " Jahrbuch," on 

 page 214. This catalogue contained eighteen stars 

 only, and all were well situated for observation in 

 what is now the German Empire : it may be of 

 interest to give them. 



First Catalogue of Variable Stars. 



o Ceti, |8 Persei, x Cygni, R Hydrae, R Leonis, v Aquilae, 

 (3 Lyrae, * Cephei, a Herculis, R Coronae Borealis, R Scuti, 

 R Virginis, R Aquarii, R Serpentis, S Serpentis, a Cassiopeiae, 

 a Ononis, a Hydrae. 



The capital letters have been added to some of 

 these stars. The stars, when read horizontally, 

 are in the order of discovery; Novae were omitted 

 by Argelander ; they are mostly bright stars, and 

 ten of these have the old Greek notation, which 

 remains in variable star nomenclature as for all 

 other astronomical purposes. Of the other eight, 

 seven have the prefix R, and one the letter S. As 

 some of the capital letters beginning at A had 

 already been used by Bayer, about two hundred 

 years earlier, Argelander formed the scheme of 

 applying the letters of the alphabet, beginning at 

 R, to the stars shown to be variable, other than 

 those already designated with Greek or other letters. 

 So soon as enough variable stars had been discovered 

 to require the letter Z, the sequence was to be con- 

 tinued with the duplication or combination of letters ; 

 thus after Z the next in the series would be R R to 

 R Z, S S to S Z, and so on to Z Z. The necessary 

 complement of these prefixes was the name of the 

 constellation ; so the full designation for a variable 

 star might be R Andromedae, R R Aquarii, or Z Z 

 Cygni. This form of nomenclature was sufficient 

 for forty-five variable stars in each constellation. 

 Until a few years ago the discovery of new variable 

 stars depended upon visual work, and this nomen- 

 clature sufficed for all needs. With the greater 

 application, or rather a closer examination, of the 

 many thousands of photographs that have been 

 taken at Harvard College and other observatories 

 (mainly at Harvard), the number of new variable 

 stars is being increased by hundreds a year; the 

 result is that the method of Argelander has broken 

 down — at least for certain constellations. 



In 1909 the number of variable stars was more 

 than forty-five (= Z Z) for the constellation of 

 Cygnus. Recourse was then had to the dual use 

 of the letters beginning with A A — single letters 

 could not be used, for, as I have pointed out, many 

 single capital letters were already in use for non- 

 variable stars. The continuance of this notation, 



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