Stellar classification

This article deals with the classification of stars in astronomy, to different classifications are listed in brief below and optionally treated in detail below.

MK and Yerkes classification

The MK- classification - according to the first letter of the last name of William Wilson Morgan and Philip C. Keenan, the system first developed - even Yerkes classification - according to the Yerkes Observatory, where they both worked - and as MKK system called, was 1943 introduced by William Wilson Morgan, Phillip C. Keenan and Edith Kellman.

This is a two-part classification scheme, which is composed of spectral types and luminosity classes. The two parts, especially the spectral types, can also be used individually for the classification of stars. The spectral types can be assigned by analysis of the spectra of stars or photometric means.

Spectral types by spectra

The spectral classes represent different areas of surface temperatures. The classification made ​​on the basis of spectral ( absorption and emission lines) in the spectra of the stars. The presence of spectral lines is directly related to the surface temperature of a star, since, depending on temperatures different elements can be ionized.

Luminosity classes ( developmental state )

The luminosity classes are an expression of the development status of stars. They are derived from certain characteristics of the spectral lines, in particular of its width and intensity. The division into a luminosity class is closely related to the luminosity, but not directly derived from the luminosity from.

Size classes (apparent brightness)

In the so-called " class size " (also called " Magnitudo " ) are ordered according to their apparent brightness of stars that are visible to the naked eye from Earth. This is the oldest way to organize stars. This classification can be determined, how easy or difficult star and other non- self-luminous objects can be observed. As the apparent brightness but essentially depends on the distance of the star, it is not suitable for astrophysical purposes.

Populations ( metal abundance )

With the help of the metal abundance is also assigns star in populations, allowing conclusions on their age. Populations roughly correspond to the emergence of a star, as the metals during the nucleosynthesis always continue to accumulate in galaxies. In other galaxies than the Milky Way, such populations may be defined differently than in the Milky Way, for example, all stars in the Magellanic Clouds metal-poor compared to the stars in the Milky Way. The star shown in the following table are sorted coarse.