A Class B star is the second-brightest type of main sequence star. They are typically colored blue-white, slightly less blue than O-type stars. They are fairly rare, making up only 0.13% of main-sequence stars. A typical Class B star has a mass of 9 (2 to 16) solar masses, a radius of 4 (2 to 7) solar radii, a luminosity of 1,000 (25 to 30,000) solar luminosities, a surface temperature of 20,000 K (10,000 K to 30,000 K), and a lifespan of 40 million years.