Spark image
Cepheid variables

These stars vary in brightness because as the two stars orbit each other they also eclipse each other.

The double star Algol (b is composed of two stars of roughly the same size but of different intensities.

As they move one of the stars is eclipsed by the other and this affects the total observed brightness of the pair. The larger dip in the light curve is when the dimmer star moves in front of the brighter one. The smaller dip is where the brighter star moves in front of the dimmer one.

 
 
 
© Keith Gibbs 2011