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
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
Star Observing Section web site.