Stars are classified by the spectral properties of their light. They are sorted into seven letter classes, from hottest to coolest: O, B, A, F, G, K, and M. Astronomers add another number and Roman numeral to categorize the star even more specifically, taking into account its size, brightness, and how close it is to the next letter in the classifying system. Our sun, for example, is a G2V star.
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Key Facts In This Video
Scientists can identify an object's chemical composition by studying its spectral properties. 00:45
Annie Jump Cannon proposed the OBAFGKM classification system for stars in the late 19th century. 01:10
Our sun's spectral type is a G2. 01:37