Variable Stars

Much has been learned from the short-term variations in brightness of certain types of stars. For the Cepheid variables, the period of variation is an indication of the absolute magnitude of the star. It is therefore an important tool for measuring astronomical distances. The RR Lyrae variables also exhibit regular periods.

There can be a stage of variability late in the red giant phase of a star's life. A whole class of variable stars have been named after the variable star officially known as Omicron Ceti but also widely known as Mira. "Mira-type" stars are variables with a period of around 100 - 1000 days and with visual light variations of more than 2.5 magnitudes. Over 6000 "Mira variables" are now known.

The extraordinary brightening of a star known as a nova is thought to be a characteristic of binary systems where there is exchange of mass, perhaps falling into a white dwarf and triggering a sudden burst of fusion. There can be multiple nova events, but not a reproducible period. A supernova is in a class by itself as a singular dramatic stellar event.

A pattern of regular intensity variation may signal the presence of a binary star or a multiple star system where eclipsing is taking place.