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http://www.teachastronomy.com/ Main sequence stars are classified according to the system of spectral types developed almost a hundred years ago. Going from the hottest to the coolest stars there are O type main sequence stars whose mass is about fifty times that of the Sun, radius about twenty times, a temperature of forty thousand degrees, and a luminosity a million times that of the Sun. B stars have masses twenty times that of the Sun and radii seven times that, photospheres are thirty thousand Kelvin and the luminosity is about twenty thousand times that of the Sun. A stars masses three times that of the Sun and radius three times, ten thousand degree atmospheres, and eighty times the Sun's luminosity. F stars mass of 1.7 times the Sun's mass and radius 1.4 times, seventy-five hundred degree Kelvin for the photosphere, and six times the luminosity of the Sun. G stars, similar to the Sun, 1.1 times the mass and the radius, six thousand degree atmospheres, and 1.3 times the Sun's luminosity. K stars 0.8 times the mass of the Sun and the same factor for the radius, five thousand degree atmospheres, and 0.4 solar luminosities. And the coolest M stars about a half the mass of the Sun, 0.6 times the solar radius, a photosphere of thirty-five hundred Kelvin and luminosity of 0.03 times the Sun's luminosity.