Hertzsprung-Russell diagram

In stellar astronomy, the Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD) shows the relationship between absolute magnitude, luminosity, stellar classification, and surface temperature. This was devised, c.1910, by Ejnar Hertzsprung and Henry Norris Russell.

Related Topics:
Stellar astronomy - Relationship - Absolute magnitude - Luminosity - Stellar classification - Temperature - 1910 - Ejnar Hertzsprung - Henry Norris Russell

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There are two equivalent forms. One is the observer's form which plots the color index of the star on one axis and the absolute magnitude on the other axis. These two quantities can be derived from observations.

Related Topics:
Color index - Absolute magnitude

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The theoretician's form plots the temperature of the star on one axis and the luminosity of the star on the other. These two quantities can be

Related Topics:
Temperature - Luminosity

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calculated from computer models.

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The exact transformation from one to the other is not trivial, and depends on the model being used and their parameters (like age and composition).

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See Sekiguchi and Fukugita, for example, for a transformation between B-V color index and temperature.

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The H-R diagram is used to define different types of stars, and to match theoretical predictions of stellar evolution using computer models with

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observations of actual stars.

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An examination of the diagram shows that stars tend to fall only into certain

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regions on the diagram. The most predominant is the diagonal, going from the

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upper-left (hot and bright) to the lower-right (cooler and less bright), called

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the main sequence. In the lower-left is where white dwarfs are found,

Related Topics:
Main sequence - White dwarf

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and above the main sequence are the red giants and supergiants. The Sun

Related Topics:
Red giant - Supergiant - Sun

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is found on the main sequence at luminosity 1 (magnitude approx. 5), around 5400K (Stellar Class G2).

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