Variable Stars

There are a great number of stars which change their brightness over time periods as short as seconds all the way up to years. There are also a number of different reasons why stars vary their light output. Some are intrinsic variables, actually changing brightness because of physical changes in the star. Others are just interacting with their orbital companions.


Pulsating VariablesThese are dying stars. As a star becomes old, its nuclear furnace becomes unstable and its light becomes unsteady. Their are Red Giant stars such as Mira which grow and shrink majestically over a year long period. There are the very important Cepheid Variables, which are important diastance indicators. Students in my class will have done a lab exercise on Cepheids.


Eclipsing Variables: Here, two stars are orbiting each other in such a way so as to block each other's light. Algol is a star in the constellation of Perseus which displays regular changes in brightness as the two stars orbit each other. See my page on Eclipsing Binary stars.


Cataclysmic Variables:These are stars which change their light suddenly and, usually, without warning. One well-known example is a supernova. There are also flare stars and recurrent novae.


The AAVSO is an orginization of primarily amateur astronomers who take on the task of recording the changing light of thousands of stars. The names of variables does not seem to make sense, at first, but there is a system, developed in the nineteenth century.


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Updated March 31, 2009