Glossary term: Spectral Type

Description: Stars are classified according to the appearance of lines in their spectrum. The spectral type is based primarily on the temperature of the stellar surface. The present notation is a legacy from the first modern classification attempt, undertaken at Harvard College Observatory. The classes originally designated A–Q, alphabetically, were subsequently reordered as a temperature sequence, resulting in the main types still used today: O, B, A, F, G, K, and M, listed in order of decreasing surface temperature. The main spectral classes are subdivided, denoted by the numbers from 0 to 9. The Sun is spectral type G2. Additional letters refer to special characteristics (such as e for stars with bright emission lines), and the luminosity class, denoted by Roman numerals, may also be specified.

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Term and definition status: This term and its definition is still awaiting approval

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