giant star

a star having a diameter of from 10 to 100 times that of the sun, as Arcturus or Aldebaran. Also, giant. Cf. supergiant star.

[1910-15]

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Star with a relatively large radius for its mass and temperature; this yields a large radiating area, so such stars are bright.

Subclasses include supergiant stars, red giants (with low temperatures, but very bright), and subgiants (with slightly reduced radii and brightness). Some giants are hundreds of thousands of times brighter than the Sun. Giants and supergiants may have masses 10–30 times that of the Sun and volumes millions of times greater and are thus low-density stars.

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▪ astronomy

      any star having a relatively large radius for its mass and temperature; because the radiating area is correspondingly large, the brightness of such stars is high. Subclasses of giants are supergiants, with even larger radii and brightness for their masses and temperatures (see supergiant star); red giants, which have low temperatures but are of great brightness; and subgiants, which have slightly reduced radii and brightness.

      Some giants have luminosities hundreds of thousands of times that of the Sun. Their position in the Hertzsprung-Russell diagram (Hertzsprung–Russell diagram) (q.v.) is above the main sequence, in which the majority of stars, called dwarf stars in contrast, fall. Masses of giants and supergiants may be 10 to 30 times that of the Sun, but their volumes are often 1,000,000 to 10,000,000 times greater. Thus, they are low-density “diffuse” stars.

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