Main sequence: Difference between revisions

Revision as of 05:15, 13 March 2024

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In 1933, [[Bengt Strömgren]] introduced the term Hertzsprung–Russell diagram to denote a luminosity-spectral class diagram.<ref name=zfa7/> This name reflected the parallel development of this technique by both Hertzsprung and Russell earlier in the century.<ref name=brown/>

As evolutionary models of stars were developed during the 1930s, it was shown that, for stars ofwith uniformthe chemicalsame composition, a relationship exists between athe star's mass anddetermines its luminosity and radius. That isConversely, forwhen a givenstar's masschemical composition and composition,its thereposition ison athe uniquemain solutionsequence forare determiningknown, the star's radiusmass and luminosityradius can be deduced. This became known as the [[Vogt–Russell theorem]]; named after [[Heinrich Vogt (astronomer)|Heinrich Vogt]] and Henry Norris Russell. By this theorem, when a star's chemical composition and its position on the main sequence are known, so too are the star's mass and radius. (However, itIt was subsequently discovered that thethis theoremrelationship breaks down somewhat for stars of the non-uniform composition.)<ref name=schatzman33/>

A refined scheme for [[stellar classification]] was published in 1943 by [[William Wilson Morgan]] and [[Philip Childs Keenan]].<ref name=keenan_morgan43/> The MK classification assigned each star a spectral type—based on the Harvard classification—and a luminosity class. The Harvard classification had been developed by assigning a different letter to each star based on the strength of the hydrogen spectral line before the relationship between spectra and temperature was known. When ordered by temperature and when duplicate classes were removed, the [[spectral type]]s of stars followed, in order of decreasing temperature with colors ranging from blue to red, the sequence O, B, A, F, G, K, and M. (A popular [[mnemonic]] for memorizing this sequence of stellar classes is "Oh Be A Fine Girl/Guy, Kiss Me".) The luminosity class ranged from I to V, in order of decreasing luminosity. Stars of luminosity class V belonged to the main sequence.<ref name=tnc/>