424 



KNOWLEDGE. 



November, 1913. 



to give them ; the designation almost always indicates 

 the constellation. The most unsatisfactory point in 

 the scheme appears to be the dual character for the 

 northern and southern stars ; if the constellation be 

 given as well as the number all would be clear for 

 stars in those constellations beyond fifteen degrees 

 from the equator. But for those, as Cetus, Orion, 

 Aquila, and so on, which embrace stars on both sides 

 of the equator some additional and distinctive 

 notation must be introduced, and Professor 

 Pickering continues his custom — as in all his 

 photometric and other work— of designating all 

 negative quantities in print in italic type. In a bad 

 light, or when using a catalogue quickly, one is apt 

 to overlook the italic type, this is the chief objection 

 to the method ; but the introduction of a minus sign 

 would give emphasis to the star being in the 

 southern hemisphere. 



Had north polar distance (N.P.D.) been adopted 

 instead of declination this difficulty would have been 

 overcome ; but N.P.D. is very seldom used in 

 practice, and not many instruments are so graduated. 



Let us see how the second Harvard Catalogue 

 looks. This is a portion of one page : — 



Two-thirds of these had no letters in 1907. 



It will be appropriate to make a quotation here 

 from The Annals of the Harvard Observatory, 

 vol. LV :— 



" The number of variable stars has now become 

 so large that it is necessary to have some convenient 

 means of referring to them and of locating them. 

 The numbers given by the editor of the Astro- 

 nomische Nachrichten, while very useful for certain 

 purposes, are not convenient as permanent reference 

 numbers for the stars. In reading an article which 

 merely gives, for instance, 21, 1909 Andromedae, one 

 is at a loss to recall just where the object is, or 

 whether it is suitably placed for observation. For 

 this purpose a list must be consulted to find the 

 position of the object. On the other hand the 

 designations used here serve to locate the star. 

 They give the hour and minute of right ascension 

 and the degree of declination. This is often all that 

 is needed. An observer can at once make up his 

 mind whether the object can be observed at present 



or at a later time. The objection has been raised 

 that six figures cannot readily be remembered. On 

 the contrary, it is found here that they cling to the 

 memory with remarkable tenacity if constantly 

 used in connection with each variable. An observer 

 here,* by whom these [numerical] designations are 

 used daily, recently made a test. He wrote down 

 the names of 367 variable stars. For 260 of these 

 stars he supplied from memory the designations 

 correct in all six figures." 



This quotation introduces the fourth form of 

 nomenclature now current. It is convenient as a 

 temporary expedient, but we think it should be 

 abandoned as being cumbersome and overlapping. 

 The Astronomische Nachrichten notes the discovery 

 of variable stars, and each year the series begins 

 with No. 1 (with the constellation added) ; so, 

 unless one is careful to add the year, confusion will 

 soon arise. From this temporary method of 

 nomenclature the star is advanced to the lettered 

 form, but that may not be until some years have 

 elapsed and the star has been proved to be variable. 

 The application of letters to the variable stars is 

 years in arrear ; the general result is that we have 

 four forms of nomenclature for variable stars in 

 current use. 



There is yet a fifth method. Each year, as 

 already mentioned, there is a catalogue of variable 

 stars edited by Hartwig, and published in the 

 Vierteljahrschrift der Ast. Gesell. ; the stars (in the 

 list for 1913) are numbered from No. 1 to 962 in 

 order of R.A. for epoch 1855-0, and include only 

 the stars to — 23° declination ; those south of— 23° 

 begin at No. 1001 to 1417, but in order of R.A. for 

 1875-0! At the end of these annual catalogues 

 there is an alphabetical arrangement of the constella- 

 tions with the appropriated letters, to which is added 

 the number in the catalogue. So, as new stars are 

 added each year, the catalogue number for, say, 

 R Aurigae will differ almost every year. As only 

 about 1,400 variable stars are given in Hartwig's 

 catalogue for 1913, and 3,748 are given in the 

 Harvard Second Catalogue to the end of 1906, it is 

 presumed that when the number 999 is reached the 

 next thousand will have to be skipped and continue 

 the northern list at 2,000 : this is encouraging 

 confusion. The epoch for the Harvard Catalogue 

 is the same convenient date as for the International 

 Astrographic Survey, 1900 ; and it would save much 

 time and be of the greatest advantage to practical 

 astronomy in all its branches, if all positions of stars, 

 whether approximate or accurate, were always given 

 for this epoch (1900-0) for the next thirty or forty 

 years, when 1950-0 might be adopted until the year 

 2000. 



Those interested in variable star work have there- 

 fore at least five forms of nomenclature and three 

 different epochs to amuse themselves with, besides 

 variations for north and south stars. In view 

 of the fact that continued rapid accessions of new 



The Observatory of Harvard College, 



