A variable star is a star of which the brightness is variable. There are several types, some of which can change in brightness within the space of a few minutes, while others change slowly over months. The first 334 variable stars discovered in a constellation were given one or two code letters such as R Scuti or UV Ceti. The others are named V335, V336 etc. e.g. Proxima Centauri is known as variable star V645 Centauri.