Trekipedia

Star, Type-M

Red star. Temperatures ranged from 2500 to 3500°K. M-Type stars were composed of ionized atoms, especially helium.

Each spectral class (O, B, A, F, G, K, M) was divided into 10 subclasses, ranging from 0 (hottest) to 9 (coolest). Stars were also divided into six categories according to luminosity: Ia (most luminous supergiants), Ib (less luminous supergiants), II (luminous giants), III (normal giants), IV (subgiants), and V (main sequence and dwarfs). For instance, Sol was classified as G2V, which meant that it was a relatively hot G-Type main sequence star. In addtion, classes R, N, S, T, Q, and W were used for relatively rare star types not found on the main sequence.^[1]