Naming Variable Stars
In the 19th century, the German astronomer Argelander decided that variable stars required a naming system of their own. By this time Beyer had used the Greek alphabet for his catalogue of the brightest stars; Flamsteed had used numbers in his catalogue; and small Roman letters and capital Roman letters up to Q had been used for the then newly charted southern constellations.
It was decided, therefore, to use capital Roman letters from R to Z to denote variable stars, for example R CrB, W Cyg and so on. Unfortunately, this catered for only nine variables per constellation - nowhere near enough! So to extend the range, double letters were used, starting with RR up to RZ, then SS to SZ, and so on up to YY, YZ and ZZ. After this came AA to AZ, BB to BZ etc. finishing with QZ. The two letters were kept in alphabetical order, for example combinations like WA, SR, BA etc. were not used. Further, the letter J was omitted to avoid confusion with I. This system allowed for 234 variables. However, constellations such as Cygnus and Sagittarius in the Milky Way soon used them all up.
It was then that a system came into use which continued the previous one, and could also include it. After QY, QZ came V235, V236 etc. This system has no limits, of course, and could be used to supersede the capital letter system: e.g. R CrB = V1 CrB, W Cyg = V6 Cyg, and so on. However, this logical system has not fully taken over and capital letters are still in common use with the number-based system taking over at V235. Some of the brighter variables had, of course, been given Greek letters by Beyer. These are still in common use and we still refer to variable stars such as β Persei or Algol, α Orionis or Betelgeuse and δ Cephei, for example.