used in astronomy
to indicate the classes (or colors) of stars
, which was OBAFGKM
or (O, B, A, F, G, K and M), on a stellar
evolution diagram ranging from hot, early type stars (O) to cool,late type stars (M) class.( Three additional classes (RNS) (or OBAFGKMRNS
) are no longer used. The mnemonic for that one was Oh Be A Fine Girl Kiss Me Right Now Sweetheart
About 200 years ago it was discovered that sunlight is not merely one color, but in fact is made up of bands of hundreds of colors. A much more complete explanation is located under Stellar Spectra, and a nice visual display is shown at Hertzsprung-Russell diagram.