Variable and Double Stars

Abstract

The bright variable star Beta Persei, or Algol, the Demon Star has been known to vary in brightness for many thousands of years. There are many over variable stars scattered around the sky. Their variability can be due to a variety of different causes. Algol itself is an unresolved double star system. When the fainter companion moves across the face of the brightest star, the amount of light reaching the observer is reduced. A much smaller reduction on brightness is seen when the fainter companion passes behind the brighter star. Another variable star Epsilon Aurigae, located close to Capella, although itself a double star system, its variation in light output is mainly due to a cloud of dark material moving around the two stars. As this dark material orbits the stars it periodically stops some of the starlight from reaching us on Earth. This change is reasonably predictable, but changes do take place over time as the material moves around. So like many things that change in the sky, it is always worth keeping track of what is happening.