Describing and Measuring Stars

How do astronomers describe and organize the types of stars in the universe?

Astronomers organize stars into types based primarily on their colors and surface temperatures. There are seven main categories of stars; they are called stellar spectral types, and each is identified by a letter—O, B, A, F, G, K, or M. Stars of Type O have the bluest colors, and the highest surface temperatures compared to other stars. On the other end, stars of Type M have the reddest colors and the lowest surface temperatures.


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