A category of intensely hot stars, whose surface temperatures range up to 50,000 K
(some nine times hotter than the surface of the Sun). O-type stars
are a brilliant blue-white in colour, and are relatively rare in comparison with their cooler cousins. Probably the two best known O-type
stars in the sky are Alnitak and
Mintaka, the two outer stars of
Orion's Belt.
