G V star
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The English used in this article may not be easy for everybody to understand. (August 2010) |
In astronomy, a G V star is a main-sequence star of spectral type G and luminosity class V on the Hertzsprung-Russell Diagram. Such a star, which can also be called a yellow dwarf, is small (about 0.8 to 1.0 solar masses) and has a surface temperature of between 5,300 and 6,000 K.[1], Tables VII, VIII. Like other main-sequence stars, a G V star turns hydrogen to helium in its core by means of nuclear fusion.[2]
(The luminosity class, expressed in Roman numerals, is not to be confused with the spectral classification sub-type, which relates to the star's color and temperature and is expressed in Arabic numbers. For example, Earth's Sun is a G2 spectral sub-type star. Luminosity class V is equivalent to saying on the main sequence. So a "G V star" simply means a yellow main-sequence star.)
Our Sun is the most commonly known (and most easily seen) example of a G V star. Each second, it combines around 600 million tons of hydrogen to helium, changing about 4 million tons of matter to energy.[3][4] Other G V stars include Alpha Centauri A, Tau Ceti, and 51 Pegasi.[5][6][7]
The term yellow dwarf is actually an incorrect name, as G stars can be any color from white, for early types like the Sun, to only slightly yellow for the older types.[8] See Spectral Classification for a chart of star color by light type. Our own Sun is in fact white, but looks yellow through the Earth's atmosphere due to what is called Rayleigh scattering. Even though the name "dwarf" is used to compare yellow main sequence stars from giant stars, yellow dwarfs like the Sun are 90% brighter than all of the stars in the Galaxy (which are largely orange dwarfs, red dwarfs, and white dwarfs).
A G V star will combine hydrogen and helium togther to make energy for around 10 billion years, until there are no more gases left to combine inside the center of the star. When this happens, the star will grow to many times its earlier size and become a red giant like the star that is named Aldebaran.[9] Eventually the red giant will lose its outer layers of gas, which will become a planetary nebula, while the inside of the star (also known as the core) will cool and shrink into a small, very heavy white dwarf.[2]
Notes [change]
- ↑ Empirical bolometric corrections for the main-sequence, G. M. H. J. Habets and J. R. W. Heintze, Astronomy and Astrophysics Supplement 46 (November 1981), pp. 193–237.
- ↑ 2.0 2.1 Stellar Evolution: Main Sequence to Giant, class notes, Astronomy 101, Valparaiso University, accessed on line June 19, 2007.
- ↑ Why Does The Sun Shine?, lecture, Barbara Ryden, Astronomy 162, Ohio State University, accessed on line June 19, 2007.
- ↑ Sun, entry at ARICNS, accessed June 19, 2007.
- ↑ Alpha Centauri A, SIMBAD query result. Accessed on line December 4, 2007.
- ↑ Tau Ceti, SIMBAD query result. Accessed on line December 4, 2007.
- ↑ 51 Pegasi, SIMBAD query result. Accessed on line December 4, 2007.
- ↑ What Color Are the Stars?, Mitchell N. Charity's webpage, accessed November 25, 2007
- ↑ SIMBAD, entry for Aldebaran, accessed on line June 19, 2007.
