G-type main-sequence star

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 yellowish for less massive and luminous G-type main-sequence stars.[http://www.vendian.org/mncharity/dir3/starcolor/ What Color Are the Stars?] {{Webarchive|url=https://web.archive.org/web/20170806143102/http://www.vendian.org/mncharity/dir3/starcolor/ |date=2017-08-06 }}, Mitchell N. Charity's webpage, accessed November 25, 2007 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.{{cite web|last1=Cain|first1=Frazer|title=WHAT COLOR IS THE SUN?|url=https://www.universetoday.com/18689/color-of-the-sun/|publisher=Universe Today|access-date=2017-11-06|archive-date=2012-03-20|archive-url=https://web.archive.org/web/20120320172751/http://www.universetoday.com/18092/temperature-of-the-sun/|url-status=live}}{{cite web|title=What Color is the Sun?|url=http://solar-center.stanford.edu/SID/activities/GreenSun.html|publisher=Stanford University|access-date=2017-11-06|archive-date=2017-10-30|archive-url=https://web.archive.org/web/20171030154449/http://solar-center.stanford.edu/SID/activities/GreenSun.html|url-status=live}}{{cite journal |last=Dissanaike |first=George |date=19 October 1991 |title=Painting the sky red |journal=New Scientist |volume=132 |number=1791 |pages=31–33}} In addition, although the term "dwarf" is used to contrast G-type main-sequence stars with giant stars or bigger, stars similar to the Sun still outshine 90% of the stars in the Milky Way (which are largely much dimmer orange dwarfs, red dwarfs, and white dwarfs which are much more common, the latter being stellar remnants).{{Cite web |title=More G Stars {{!}} StarDate Online |url=https://stardate.org/radio/program/2018-10-21#:~:text=The%20Sun%20belongs%20to%20a,in%20the%20Milky%20Way%20galaxy. |access-date=2022-04-22 |website=stardate.org}}

A G-type main-sequence star with the mass of the Sun will fuse hydrogen for approximately 10 billion years, until the hydrogen element is exhausted at the center of the star. When this happens, the star rapidly expands, cooling and darkening as it passes through the subgiant branch and ultimately expanding into many times its previous size at the tip of the red giant phase, about 1 billion years after leaving the main sequence. After this, the star's degenerate helium core abruptly ignites in a helium flash fusing helium, and the star passes on to the horizontal branch, and then to the asymptotic giant branch. Expanding even further as helium starts running out as it pulses violently, the star's gravity is not sufficient to hold its outer envelope, resulting in significant mass loss and shedding. The ejected material remains as a planetary nebula, radiating as it absorbs energetic photons from the photosphere. Eventually, the core begins to fade as nuclear reactions cease, and becomes a dense, compact white dwarf, which cools slowly from its high initial temperature as the nebula fades.{{cite journal |last1=Hurley |first1=J. R. |last2=Pols |first2=O. R. |last3=Tout |first3=C. A. |title=Comprehensive analytic formulae for stellar evolution as a function of mass and metallicity |journal=Monthly Notices of the Royal Astronomical Society |date=1 July 2000 |volume=315 |issue=3 |pages=543–569 |doi=10.1046/j.1365-8711.2000.03426.x|doi-access=free |arxiv=astro-ph/0001295 |bibcode=2000MNRAS.315..543H |s2cid=18523597 }}{{Cite web |title=Evolution from the Main Sequence to Red Giants {{!}} Astronomy |url=https://courses.lumenlearning.com/astronomy/chapter/evolution-from-the-main-sequence-to-red-giants/ |access-date=2022-04-22 |website=courses.lumenlearning.com}}

The revised Yerkes Atlas system (Johnson & Morgan 1953)[http://adsabs.harvard.edu/abs/1953ApJ...117..313J Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas] {{Webarchive|url=https://web.archive.org/web/20190402140913/http://adsabs.harvard.edu/abs/1953ApJ...117..313J |date=2019-04-02 }} H.L. Johnson & W.W. Morgan, 1953, Astrophysical Journal, 117, 313 listed 11 G-type dwarf spectral standard stars; however, not all of these still exactly 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 Chara (G0V), the Sun (G2V), Kappa1 Ceti (G5V), 61 Ursae Majoris (G8V).[http://www.astro.utoronto.ca/~garrison/mkstds.html MK ANCHOR POINTS] {{Webarchive|url=https://web.archive.org/web/20190625094716/http://www.astro.utoronto.ca/~garrison/mkstds.html |date=2019-06-25 }}, Robert F. Garrison Other primary MK standard stars include HD 115043 (G1V) and 16 Cygni B (G3V).[http://adsabs.harvard.edu/abs/1989ApJS...71..245K The Perkins Catalog of Revised MK Types for the Cooler Stars] {{Webarchive|url=https://web.archive.org/web/20171011055147/http://adsabs.harvard.edu/abs/1989ApJS...71..245K |date=2017-10-11 }}, P.C. Keenan & R.C McNeil, "Astrophysical Journal Supplement Series" 71 (October 1989), pp. 245–266. 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 (G6V). There are not yet any generally agreed upon G7V and G9V standards.

{{Main|Habitability of yellow dwarf systems}}

G-type main sequence stars can provide habitability for life to develop, such as the Sun with life on Earth.{{cite web |last=Mullen |first=Leslie |date=18 May 2001 |title=Galactic Habitable Zones |url=http://www.astrobio.net/news-exclusive/galactic-habitable-zones/ |url-status=live |archive-url=https://web.archive.org/web/20110807024530/http://www.astrobio.net/exclusive/139/galactic-habitable-zones |archive-date=7 August 2011 |access-date=1 June 2020 |work=Astrobiology Magazine}} They also live long enough to give life enough time to develop, between 7.9 and 13 billion years. Our Sun’s lifetime is about 10 billion years.{{Cite web |title=Stellar Lifetimes |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/startime.html |access-date=2024-07-20 |website=hyperphysics.phy-astr.gsu.edu}}

Besides the Sun and its planets, some of the nearest G-type stars known to have planets include 61 Virginis, HD 102365, HD 147513, Chalawan, Cervantes and Tau Ceti.

• G-dwarf problem
• Hertzsprung–Russell diagram
• Solar analog
• Star count, survey of stars
• Yellow hypergiant

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{{Commons category-inline|Yellow dwarfs}}

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Category:Star types