Beta Persei

Bearing the Beta designation of Perseus, Algol is a blue-white B-type star whose colour index of −0.003 sits at the boundary between the blue-white and white spectral ranges. It lies about 90 light-years away and shines at apparent magnitude 2.09. Its absolute magnitude of −0.11 indicates an intrinsic luminosity somewhat above that of the Sun-like stars, though far below the distant supergiants; the close match between its apparent and absolute figures is consistent with its moderate distance. Algol occupies the figure of Perseus and, at magnitude 2.09, is one of the constellation's most conspicuous stars to the unaided eye, a prominence that secured it a place among the most storied of the traditional named stars.