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A G-type main-sequence star
G-type main-sequence star
(Spectral type: G-V), often (and imprecisely) called a yellow dwarf, or G dwarf 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
G-type main-sequence star
is converting the element hydrogen to helium in its core by means of nuclear fusion.[3] The Sun, the star to which the Earth
Earth
is gravitationally bound in the Solar System
Solar System
and the object with the largest apparent magnitude, is an example of a G-type main-sequence star
G-type main-sequence star
(G2V type). Each second, the Sun
Sun
fuses approximately 600 million tons of hydrogen to 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
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
Sun
is in fact white, and its spectrum peaks in blue and green light, 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 from giant stars, yellow dwarfs like the Sun
Sun
outshine 90% of the stars in the Milky Way
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
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
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.[3]

Contents

1 Spectral standard stars 2 Planets 3 See also 4 Notes 5 References 6 External links

Spectral standard stars[edit] The revised Yerkes Atlas system (Johnson & Morgan 1953)[14] listed 11 G-type dwarf spectral standard stars; however, not all of these have survived to this day as standards. The "anchor points" of the MK spectral classification
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
Sun
(G2V), Kappa1 Ceti
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
82 Eridani
(G8V). There are not yet any generally agreed upon G7V and G9V standards. Planets[edit] 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, Tau Ceti and Alpha Centauri. See also[edit]

Star
Star
portal Astronomy portal

Brown dwarf Hertzsprung–Russell diagram K-type main-sequence star Red dwarf Solar twin Star
Star
count, survey of stars Stellar classification, class G

Notes[edit]

^ The Sun
Sun
is not in this class because even though it corresponds to the same mass, the Sun
Sun
is slightly hotter than the typical temperature for a G5V star (at 5,778 K), so it is a G2V star, which is normally slightly more massive than the Sun

References[edit]

^ Vardavas, Ilias M.; et al. (2011), "Chapter 5. Incoming Solar Radiation", Radiation and Climate: Atmospheric Energy
Energy
Budget from Satellite Remote Sensing, International Series of Monographs on Physics, 138, OUP Oxford, p. 130, ISBN 0199697140  ^ 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. ^ a b Stellar Evolution: Main Sequence to Giant[permanent dead link], class notes, Astronomy 101, Valparaiso University, accessed on line June 19, 2007. ^ Why Does The Sun
Sun
Shine?, lecture, Barbara Ryden, Astronomy 162, Ohio State University, accessed on line June 19, 2007. ^ Sun
Sun
Archived 2007-06-16 at the Wayback Machine., entry at ARICNS, accessed June 19, 2007. ^ Alpha Centauri
Alpha Centauri
A, SIMBAD
SIMBAD
query result. Accessed on line December 4, 2007. ^ Tau Ceti, SIMBAD
SIMBAD
query result. Accessed on line December 4, 2007. ^ 51 Pegasi, SIMBAD
SIMBAD
query result. Accessed on line December 4, 2007. ^ What Color Are the Stars?, Mitchell N. Charity's webpage, accessed November 25, 2007 ^ Cain, Frazer. "WHAT COLOR IS THE SUN?". Universe Today.  ^ "What Color is the Sun?". Stanford University.  ^ Dissanaike, George (19 October 1991). "Painting the sky red". New Scientist. 132 (1791): 31–33.  ^ SIMBAD, entry for Aldebaran, accessed on line June 19, 2007. ^ Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas H.L. Johnson & W.W. Morgan, 1953, Astrophysical Journal, 117, 313 ^ MK ANCHOR POINTS, Robert F. Garrison ^ The Perkins Catalog of Revised MK Types for the Cooler Stars, P.C. Keenan & R.C McNeil, "Astrophysical Journal Supplement Series" 71 (October 1989), pp. 245–266.

External links[edit] Media related to Yellow dwarfs at Wikimedia Commons Also known as G2V

v t e

Star

Formation

Accretion Molecular cloud Bok globule Young stellar object Protostar Pre-main-sequence star

Herbig Ae/Be Orion

T Tauri FU Orionis

Herbig–Haro object Hayashi track Henyey track

Evolution

Main sequence Red giant
Red giant
branch Horizontal branch

Red clump

Asymptotic giant branch Protoplanetary nebula Planetary nebula PG1159 star Dredge-up Instability strip Luminous blue variable Blue straggler Stellar population Supernova Supernova
Supernova
impostor Hypernova Hertzsprung–Russell diagram Color–color diagram

Luminosity class

Subdwarf Dwarf

Blue Red White Yellow Brown

Subgiant Giant

Blue Red Yellow

Bright giant Supergiant

Blue Red Yellow

Hypergiant

Yellow

Spectral classification

O B A F G K M WR Be OB Subdwarf
Subdwarf
O Subdwarf
Subdwarf
B Late-type Chemically peculiar

Am Ap/Bp Barium Carbon CH CN Extreme helium Lambda Boötis Lead HgMn S Technetium

Shell

Remnants

White dwarf

Helium
Helium
planet

Neutron star

Radio-quiet Pulsar

Binary X-ray

Magnetar

Stellar black hole X-ray binary

Burster

Theoretical stars

Black dwarf Exotic

Quark Strange Preon Planck Electroweak star

Dark-matter star Dark-energy star Black star Gravastar Frozen star Q star Quasi-star Thorne–Żytkow object Iron star Blitzar

Nucleosynthesis

Deuterium burning Lithium burning Proton–proton chain CNO cycle Helium
Helium
flash Triple-alpha process Alpha process Carbon burning Neon burning Oxygen burning Silicon burning S-process R-process Fusor Nova

Symbiotic Remnant Luminous red nova

Structure

Core Convection zone

Microturbulence Oscillations

Radiation zone Atmosphere

Photosphere Starspot Chromosphere Corona

Stellar wind

Bubble Bipolar outflow

Accretion disk Asteroseismology

Helioseismology

Eddington luminosity Kelvin–Helmholtz mechanism

Properties

Designation Dynamics Effective temperature Kinematics Magnetic field Absolute magnitude Mass Metallicity Rotation UBV color Variable star

Mira variable

Star
Star
systems

Binary

Contact Common envelope Eclipsing Symbiotic

Multiple Star
Star
cluster

Open cluster Globular cluster Super star cluster

Planetary system Earth's Solar System

Earth-centric observation of

Pole star Circumpolar star Constellation Asterism Magnitude

Apparent Extinction Photographic

Radial velocity Proper motion Parallax Photometric-standard star

Lists

Star
Star
names

Arabic Chinese

Extremes Most massive Highest temperature Largest volume Smallest volume Brightest

Historical

Most luminous Nearest

Nearest bright

Stars with exoplanets Brown dwarfs White dwarfs Milky Way
Milky Way
novae Notable supernovae

Supernova
Supernova
candidates

Supernova
Supernova
remnants Planetary nebulae Timeline of stellar astronomy

Related articles

Substellar object

Brown dwarf Sub-brown dwarf Planet

Galactic year Galaxy Supercluster Guest star Gravity Icarus (most distant individual star) Intergalactic star Infrared dark cloud Starfield

Category:Stars

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