It extends on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constellation in which the star lies.
The current naming system is:[1] The second letter is never nearer the beginning of the alphabet than the first, e.g., no star can be BA, CA, CB, DA and so on.
In the early 19th century few variable stars were known, so it seemed reasonable to use the letters of the Latin script.
Because very few constellations contained stars with uppercase Latin-letter Bayer designation greater than Q, the letter R was chosen as a starting point so as to avoid confusion with letter spectral types or the (now rarely used) Latin-letter Bayer designations.
[citation needed] After two subsequent supplementary double-lettering systems hit similar limits, numbers were finally introduced.