Variable star nomenclatur

http://www.spiritus-temporis.com/variable-star/variable-star-nomenclature.html

In a given constellation, the first variable stars discovered were designated with letters R through Z, e.g. R Andromedae. (This system of nomenclature was developed by Friedrich W. Argelander, who noted that many variable stars were red and so began the naming with the letter R for rot (Red).) Letters RR through RZ, SS through SZ, up to ZZ are used for the next discoveries, e.g. RR Lyrae. Later discoveries used letters AA through AZ, BB through BZ, and up to QQ through QZ (with J omitted). Once those 334 combinations are exhausted, variables are numbered in order of discovery, and prefixed with V, e.g. V1500 Cygni.