Stellar classification
Stars are also grouped into spectral types or classes by color. In general, a star's temperature determines its color, from red to blue-white. Spectral types are named with a letter. The seven main types are M, K, G, F, A, B and O. M stars are the coldest stars and O stars are the hottest. The full system contains other types that are hard to find: W, R, N, and S. There are also "failed" stars, called brown dwarfs, have spectral types of L, T, and Y.