Blue supergiants (luminosity class I, spectral class O or B) are among the most powerful stars in existence. While not as bright or large as the red supergiants, they still pack immense power. Typically they are 20,000 to 50,000 times brighter than the Sun, 10 to 50 times heavier and 25 times larger. An example of a blue supergiant is Rigel, in the constellation Orion.