In the sequence O, B, A, F, G, K, and M used for spectral classes, which letter denotes the coolest stars?

Answer

M.

The spectral classes move sequentially from hottest (O) to coolest (M). Coolest stars settle below 3,500 Kelvin.

In the sequence O, B, A, F, G, K, and M used for spectral classes, which letter denotes the coolest stars?
temperaturepropertystarmassphysical