ALGOL (b Persei)

An animation (353KB) of the eclipsing binary's light variation over a period of 10 hours on the 1st January 2002. The system remains at constant brightness of magnitude 2.1 for approx 2 days 10 hours before rapidly fading in brightness to magnitude 3.4; the eclipse lasts 10 hours and repeats like clockwork every 2.87 days.

Named by ancient Arabian astronomers as Algol, "The Demon Star", it was most probably the first variable star to be recognised. It is the best example of an eclipsing binary system, the variability being due to the partial eclipse of a normal B type star by a mysterious dark companion.

If you would like to see Algol's variability for yourself, predictions for the timing of minima are found in many popular Astronomy magazines, such as Astronomy Now, or on the British Astronomical Association Variable Star Observing Section web site.