Variable Stars are stars that change brightness. Their brightness can change from just a fraction (not even noticeable to the naked eye) up to 20 magnitudes. To get an idea of how much a magnitudes is, consider that the difference between brightest star one can see outside at night (in a fairly dark area) and the dimmest is about 6 magnitude. Over 300,000 variable stars are known and have been cataloged.- Category ID : 416998