spectral class, in astronomy, a classification of the stars by their spectrum and luminosity. In 1885, E. C. Pickering began the first extensive attempt to classify the stars spectroscopically. This work culminated in the publication of the Henry Draper Catalogue (1924), which lists the spectral classes of 255,000 stars. The stars are divided into 7 classes designated by the letters O, B, A, F, G, K, and M; the hottest stars (O and B) are blue-white in color, while the coolest (M) are red. Each of the letter classes has subdivisions indicated by numerals 0 through 9. Thus, a B0 is the hottest B-type star, B5 is halfway between types B and A, and B9 is only slightly hotter than type A. The table entitled Spectral Classes for Main Sequence Stars gives the characteristics of the seven principal types. To the seven main groups, four more groups have since been added. R, N, and S are classes similar to the K and M types but denote somewhat different spectral characteristics; W indicates a Wolf-Rayet star, the hottest type of star that shines with a steady light. According to a system introduced by W. W. Morgan and others, a Roman numeral is added to the spectral class to specify the luminosity, or intrinsic intensity, of a star. A bright supergiant is Ia, a faint supergiant is Ib, a bright giant is II, a normal giant is III, a subgiant is IV, and a normal dwarf or main-sequence star is V. For example, Sirius is classed as A1 V, a main-sequence white star. Betelgeuse, M2 Ia, is a bright red supergiant. See also Hertzsprung-Russell diagram.
"spectral class." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (December 13, 2018). https://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/spectral-class
"spectral class." The Columbia Encyclopedia, 6th ed.. . Retrieved December 13, 2018 from Encyclopedia.com: https://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/spectral-class
Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).
Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.
Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:
Modern Language Association
The Chicago Manual of Style
American Psychological Association
- Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
- In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.