Binary system Algol. Computer artwork of the binary system Algol (Beta Persei). A blue spectral class B8 star with a diameter of 3 solar diameters and a red-yellow spectral class K2 star of about 3.5 solar diameters are in very close orbit around each other, and a ring of tenuous gas surrounds the blue star, stolen from its partner. This binary star system is around 93 light years from Earth, in the constellation of Pegasus.