red giant definition of red giant in the Free Online Encyclopedia.

red giant, star star, hot incandescent sphere of gas, held together by its own gravitation , and emitting light and other forms of electromagnetic radiation whose ultimate source is nuclear energy .
..... Click the link for more information. that is relatively cool but very luminous because of its great size. All normal stars are expected to pass eventually through a red-giant phase as a consequence of stellar evolution stellar evolution, life history of a star , beginning with its condensation out of the interstellar gas (see interstellar matter ) and ending, sometimes catastrophically, when the star has exhausted its nuclear fuel or can no longer adjust itself to a stable
..... Click the link for more information. . As a star uses up its hydrogen by converting it to helium, its central core contracts while the outer layers expand and cool; this process produces the low temperature and large size (from 10 to 1,500 times that of the sun) that characterize the red giant. Although most giant stars are red, some prominent giant stars are other colors near the red end of the spectrum, e.g., Arcturus Arcturus (ärkt
..... Click the link for more information. (orange), Aldebaran Aldebaran (ăl'dĕb`ərən), brightest star in the constellation Taurus ; Bayer designation α Tauri; 1992 position R.A.
..... Click the link for more information. (orange), and Capella Capella, brightest star in the constellation Auriga ; Bayer designation α Aurigae; 1992 position R.A. 5^h16.1^m, Dec. +45°59'. Capella is a yellow giant star of spectral class G8 III and is also a spectroscopic binary star with a
..... Click the link for more information. (yellow). The largest and brightest stars (excluding supernovas supernova, a massive star in the latter stages of stellar evolution that suddenly contracts and then explodes, increasing its energy output as much as a billionfold.
..... Click the link for more information. ) are classed as supergiants. Blue supergiants, e.g., Rigel Rigel (rī`jəl), bright star in the constellation Orion ; Bayer designation Beta Orionis; 1992 position R.A. 5^h14.
..... Click the link for more information. , are young stars on the main sequence of the Hertzsprung-Russell diagram Hertzsprung-Russell diagram [for Ejnar Hertzsprung and H. N. Russell ], graph showing the luminosity of a star as a function of its surface temperature. The luminosity, or absolute magnitude , increases upwards on the vertical axis; the temperature (or some
..... Click the link for more information. , whereas red supergiants, e.g., Betelgeuse Betelgeuse (bēt`əlj
..... Click the link for more information. and Antares Antares (ăntâr`ēz), brightest star in the constellation Scorpius ; Bayer designation Alpha Scorpii; 1992 position R.A.
..... Click the link for more information. , are old, highly evolved stars.