Stellar classification Totally Explained

Everything about Stellar Classification totally explained

In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. Stellar temperatures can be classified by using Wien's displacement law, but this poses difficulties for distant stars. Stellar spectroscopy offers a way to classify stars according to their absorption lines; particular absorption lines can be observed only for a certain range of temperatures because only in that range are the involved atomic energy levels populated. An early scheme (from the 19th century) ranked stars from A to Q, which is the origin of the currently used spectral classes.

Secchi classes

During the 1860s and 1870s, pioneering stellar spectroscopist Father Angelo Secchi created the Secchi classes in order to classify observed spectra. By 1868, he'd developed four classes of stars:

Class I: white and blue stars with broad heavy hydrogen lines (modern class A)
Class II: yellow stars—hydrogen less strong, but evident metallic lines (modern classes G and K)
Class III: orange to red stars with complex band spectra (modern class M)
Class IV: red stars with significant carbon bands and lines (carbon stars) In 1878, he added a fifth class:

Harvard spectral classification

Harvard one-dimensional (temperature) classification scheme (based on hydrogen Balmer line strengths) was developed at Harvard College Observatory in about 1912 by Annie Jump Cannon and Edward C. Pickering. The common classes are normally listed from hottest to coldest (with mass, radius and luminosity compared to the Sun) and are given in the following table.

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