G-type main-sequence star

From Wikipedia
The Sun, a typical example of a G-type main-sequence star
Properties of typical G-type main-sequence stars [1]
Mass ( M) Surface

(log g)


(B − V)
G0V 1.15 4.32 5,980 0.583
G1V 1.10 4.34 5,900 0.608
G2V 1.07 4.35 5,800 0.625
G3V 1.04 4.37 5,710 0.642
G4V [note 1] 1.00 4.38 5,690 0.657
G5V 0.98 4.40 5,620 0.672
G6V 0.93 4.42 5,570 0.690
G7V 0.90 4.44 5,500 0.713
G8V 0.87 4.46 5,450 0.740
G9V 0.84 4.48 5,370 0.776

A G-type main-sequence star (Spectral type: G-V), often called a yellow dwarf, or G star, is a main-sequence star (luminosity class V) of spectral type G. Such a star has about 0.84 to 1.15 solar masses and surface temperature of between 5,300 and 6,000 K. [2], Tables VII, VIII. Like other main-sequence stars, a G-type main-sequence star is converting the element hydrogen to helium in its core by means of nuclear fusion.[ permanent dead link] [3] The Sun, the star to which the Earth is gravitationally bound in the Solar System, is an example of a G-type main-sequence star (G2V type). Each second, the Sun fuses approximately 600 million tons of hydrogen into helium in a process known as the proton–proton chain (4 hydrogens form 1 helium), converting about 4 million tons of matter to energy. [4] [5] Besides the Sun, other well-known examples of G-type main-sequence stars include Alpha Centauri A, Tau Ceti, and 51 Pegasi. [6] [7] [8]

The term yellow dwarf is a misnomer, because G-type stars actually range in color from white, for more luminous types like the Sun, to only very slightly yellow for the less massive and luminous G-type main-sequence stars. [9] The Sun is in fact white, but it can often appear yellow, orange or red through Earth's atmosphere due to atmospheric Rayleigh scattering, especially at sunrise and sunset. [10] [11] [12] In addition, although the term "dwarf" is used to contrast yellow main-sequence stars with giant stars, yellow dwarfs like the Sun outshine 90% of the stars in the Milky Way (which are largely much dimmer orange dwarfs, red dwarfs, and white dwarfs, the last being a stellar remnant).

A G-type main-sequence star will fuse hydrogen for approximately 10 billion years, until it is exhausted at the center of the star. When this happens, the star expands to many times its previous size and becomes a red giant, such as Aldebaran (or Alpha Tauri). [13] Eventually the red giant sheds its outer layers of gas, which become a planetary nebula, while the core rapidly cools and contracts into a compact, dense white dwarf.[ permanent dead link] [3]

Spectral standard stars

The revised Yerkes Atlas system (Johnson & Morgan 1953) [14] listed 11 G-type dwarf spectral standard stars; however, not all of these still conform to this designation.

The "anchor points" of the MK spectral classification system among the G-type main-sequence dwarf stars, i.e. those standard stars that have remained unchanged over years, are beta CVn (G0V), the Sun (G2V), Kappa1 Ceti (G5V), 61 Ursae Majoris (G8V). [15] Other primary MK standard stars include HD 115043 (G1V) and 16 Cygni B (G3V). [16] The choices of G4 and G6 dwarf standards have changed slightly over the years among expert classifiers, but often-used examples include 70 Virginis (G4V) and 82 Eridani (G8V). There are not yet any generally agreed upon G7V and G9V standards.


Some of the nearest G-type stars known to have planets include the Sun, 61 Virginis, HD 102365, HD 147513, 47 Ursae Majoris, Mu Arae, and Tau Ceti.

See also


  1. ^ The Sun is not in this class because even though it corresponds to the same mass, the Sun is slightly hotter than the typical temperature for a G4V star (at 5,778 K), so it is a G2V star, which is normally slightly more massive than the Sun


  1. ^ Vardavas, Ilias M.; et al. (2011), "Chapter 5. Incoming Solar Radiation", Radiation and Climate: Atmospheric Energy Budget from Satellite Remote Sensing, International Series of Monographs on Physics, 138, OUP Oxford, p. 130, ISBN  978-0199697144, archived from the original on 2016-05-20, retrieved 2015-12-21
  2. ^ Empirical bolometric corrections for the main-sequence Archived 2019-07-17 at the Wayback Machine, G. M. H. J. Habets and J. R. W. Heintze, Astronomy and Astrophysics Supplement 46 (November 1981), pp. 193–237.
  3. ^ a b Stellar Evolution: Main Sequence to Giant[ permanent dead link], class notes, Astronomy 101, Valparaiso University, accessed on line June 19, 2007.
  4. ^ Why Does The Sun Shine? Archived 2006-09-09 at the Wayback Machine, lecture, Barbara Ryden, Astronomy 162, Ohio State University, accessed on line June 19, 2007.
  5. ^ Sun Archived 2007-06-16 at the Wayback Machine, entry at ARICNS, accessed June 19, 2007.
  6. ^ Alpha Centauri A Archived 2019-04-28 at the Wayback Machine, SIMBAD query result. Accessed on line December 4, 2007.
  7. ^ Tau Ceti Archived 2019-04-28 at the Wayback Machine, SIMBAD query result. Accessed on line December 4, 2007.
  8. ^ 51 Pegasi Archived 2019-04-28 at the Wayback Machine, SIMBAD query result. Accessed on line December 4, 2007.
  9. ^ What Color Are the Stars? Archived 2017-08-06 at the Wayback Machine, Mitchell N. Charity's webpage, accessed November 25, 2007
  10. ^ Cain, Frazer. "WHAT COLOR IS THE SUN?". Universe Today. Archived from the original on 2012-03-20. Retrieved 2017-11-06.
  11. ^ "What Color is the Sun?". Stanford University. Archived from the original on 2017-10-30. Retrieved 2017-11-06.
  12. ^ Dissanaike, George (19 October 1991). "Painting the sky red". New Scientist. 132 (1791): 31–33.
  13. ^ SIMBAD, entry Archived 2013-06-25 at WebCite for Aldebaran, accessed on line June 19, 2007.
  14. ^ Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas Archived 2019-04-02 at the Wayback Machine H.L. Johnson & W.W. Morgan, 1953, Astrophysical Journal, 117, 313
  15. ^ MK ANCHOR POINTS Archived 2019-06-25 at the Wayback Machine, Robert F. Garrison
  16. ^ The Perkins Catalog of Revised MK Types for the Cooler Stars Archived 2017-10-11 at the Wayback Machine, P.C. Keenan & R.C McNeil, "Astrophysical Journal Supplement Series" 71 (October 1989), pp. 245–266.

External links

Media related to Yellow dwarfs at Wikimedia Commons Also known as G2V