Stellar classification (astrophysics)

Stars are classed by various properties. A common classification is surface temperature. Beginning with early spectral schema in the 19th century ranking stars from A to P, the spectral classification, called “Morgan-Keenan spectral classification” now ranks stars in seven main types: A, B, A, F, G, K, M. Each spectral classification is further divided into tenths. Our sun, Sol is a G2.

Classification system

The stars are ranked from hottest to coldest:

Class Temperature Star colour

• O 30,000-60,000 °K Blue
• B 10,000-30,000 °K Blue
• A 7,500-10,000 °K White
• F 6,000-7,500 °K White (yellowish)
• G 5,000-6,000 °K Yellow (e.g. Earth’s sun)
• K 3,500-5,000 °K Orange
• M 2,000-3,5000 °K Red