523 Specific celestial bodies and phenomena

Harvard Spectral Classification Scheme

"The modern stellar spectral classification scheme (also known as the Harvard Spectral Classification Scheme) was created by Annie Jump Cannon through her examination of spectra from 1918 to 1924. Originally, the scheme used capital letters running alphabetically, but was later reordered to reflect the surface temperatures of stars. In order of decreasing temperature, these types were O, B, A, F, G, K and M. Three additional categories also in the scheme: R, N, and S types, were later realized to represent stars with peculiar heavy-metal abundances.

Atlas of Stellar Spectra

"The Atlas of Stellar Spectra and the accompanying outline have been prepared from the viewpoint of the practical stellar astronomer. Problems connected with the astrophysical interpretation of the spectral sequence are not touched on; as a consequence, emphasis is placed on ``ordinary'' stars. These are the stars most important statistically and the only ones suitable for large-scale investigations of galactic structure.

"The Atlas of Stellar Spectra and the accompanying outline have been prepared from the viewpoint of the practical stellar astronomer. Problems connected with the astrophysical interpretation of the spectral sequence are not touched on; as a consequence, emphasis is placed on ``ordinary'' stars. These are the stars most important statistically and the only ones suitable for large-scale investigations of galactic structure.

Digital Spectral Classification Atlas

"The MK Spectral classification system was founded by W. W. Morgan and P. C. Keenan in the year 1943, with the publication of the first photographic spectral classification atlas, 'An Atlas of Stellar Spectra' (Morgan, Keenan & Kellman 1943). Since that time, the MK system has been extensively revised and refined by Morgan, Keenan and others. In the late 1970's, two important spectral atlases, summarizing the development of the MK system up until that time, were published.

"The MK Spectral classification system was founded by W. W. Morgan and P. C. Keenan in the year 1943, with the publication of the first photographic spectral classification atlas, 'An Atlas of Stellar Spectra' (Morgan, Keenan & Kellman 1943). Since that time, the MK system has been extensively revised and refined by Morgan, Keenan and others. In the late 1970's, two important spectral atlases, summarizing the development of the MK system up until that time, were published.