A mnemonic is a device used to remember something. One mnemonic used by 1920s Harvard students to remember the O, B, A, F, G, K and M star types is "Oh Be A Fine Girl, Kiss Me." A more modern mnemonic from the University of California Berkeley campus is "Oh Buy A Fine Green Kilo Man." A political mnemonic used at Cal Tech in the 1970s is "On Bad Afternoons Fermented Grapes Keep Mrs. Richard Nixon Smiling."
O, B and A stars are blue. O stars are hotter than 25,000 degrees Kelvin. B stars are between 11,000 and 25,000 degrees Kelvin. The mass of O stars is 60 times more than the mass of our sun. The mass of O stars is 17 times more than the sun. Lacerta 10 is an O star. Spica and Rigel are B stars.
A stars are between 7,500 and 11,000 degrees Kelvin. The mass of this type of star is approximately 3.2 times the mass of our sun. Sirius is an A star.
F stars are blue-to-white and G stars are white-to-yellow in color. These are substantially cooler than blue stars, with F stars being between 6,000 and 7,500 degrees Kelvin and G stars being 5,000 to 6,000 degrees Kelvin. F stars have 1.7 times the mass of our sun. G stars have masses more comparable to the sun, which falls into this category.
K stars are orange-to-red in color and M stars are red. They are smaller than the sun, both with respect to mass and diameter. Aldebaran is a K star. Betelgeuse and Antares are M stars. These are very faint stars. K stars have two-fifths the luminosity of the sun and M stars have less than 1 percent of the sun's luminosity