"OBAFGKM" is a quick listing of the classification of stars using the Morgan-Keenan method of classification, which bases star class on temperature and spectra. A common mnemonic used to remember the classes is "Oh Be A Fine Girl, Kiss Me."
Class O stars are bluish in color, and are the hottest stars at over 31,000 degrees Kelvin. Class B stars are blue-white, with a temperature ranging from 9,759 to 31,000 degrees Kelvin. Class A stars range from 7,100 to 9,750 degrees Kelvin and burn white. Class F stars are yellowish-white, with temperatures ranging from 5,950 to 7,100 degrees Kelvin. Sol is a class G star, and is yellowish and burns between 5,250 and 5,950 degrees Kelvin. Class K stars burn orange at 3,800 to 5,250 degrees Kelvin, while class M stars are reddish and have the lowest temperatures at 2,200 to 3,800 degrees Kelvin.