--- title: G-type main-sequence star canonical_url: https://paxabyssi.com/wiki/G-type_main-sequence_star markdown_url: https://paxabyssi.com/wiki/G-type_main-sequence_star.md type: wiki-page revision_id: 419 revision_view: stable last_updated: 2026-09-27 license: CC BY-SA 4.0 license_url: https://creativecommons.org/licenses/by-sa/4.0/ science_status: - observed - sim summary: A hydrogen-burning star of spectral class G, like the Sun, with a surface temperature of about 5,300 to 6,000 K and roughly 0.9 to 1.1 times the Sun's mass. Often called yellow dwarfs, they look white with a faint warm tint from space and shine steadily for about ten billion years. categories: - Stars - Main-sequence stars - G-type stars aliases: - G-type star - G dwarf - G dwarfs - Yellow dwarf - Yellow dwarfs - G-type main-sequence stars - GV star - Solar-type star - Sun-like star - Solar twin - YDW - Yellow dwarf star infobox: type: star_class code: YDW mass: unit: M_Sun value: about 0.90 to 1.06 (G9V to G0V) source: observed name: G-type main-sequence star image: File:Sun_SDO_HMI_continuum.jpg radius: unit: R_Sun value: about 0.85 to 1.10 source: observed caption: "Observation: the Sun in visible light from NASA's Solar Dynamics Observatory, 20 February 2013, with sunspots. Credit: NASA/SDO/HMI/Goddard Space Flight Center" activity: Moderate; magnetic cycles like the Sun's 11-year sunspot cycle; more active when young subtypes: YDW-EG early and YDW-LG late G, each active (AC), moderate (MD) or quiet (QT) (sim codes) bv_colour: unit: mag value: 0.60 (G0V) to 0.78 (G9V); the Sun 0.65 source: observed luminosity: unit: L_Sun value: about 0.55 to 1.35 source: observed science_doc: The sim's yellow dwarf science reference last_verified: 2026-09-27, writer B real_examples: The Sun (G2V), Alpha Centauri A (G2V), Tau Ceti (G8V), 18 Scorpii (G2Va), 51 Pegasi (G2IV) habitable_zone: unit: AU value: G0V about 1.09 to 1.92; the Sun 0.95 to 1.68; G9V about 0.73 to 1.30 (conservative, Kopparapu et al. 2014) source: model physics_engine: Yellow dwarf physics engine and subtype classifier share_of_stars: About 5% of stars within 10 pc (18 of 337) luminosity_class: V perceived_colour: White with a faint yellow tint from space; the name 'yellow dwarf' exaggerates it planet_occurrence: Planets common; the Sun's family is one of many architectures stellar_class_key: yellow_dwarf absolute_magnitude_v: unit: mag value: 4.48 (G0V) to 5.55 (G9V); the Sun 4.80 (G2V) source: observed effective_temperature: unit: K value: about 5,300 to 6,000 (G0V 5,930; G2V 5,770; G9V 5,380); the Sun 5,772 source: observed main_sequence_lifetime: unit: Gyr value: about 10 for the Sun; longer for later G types, shorter for earlier source: model spectral_types_covered: G0V to G9V related: - https://paxabyssi.com/wiki/K-type_main-sequence_star.md - https://paxabyssi.com/wiki/Red_dwarf.md - https://paxabyssi.com/wiki/Red_giant.md - https://paxabyssi.com/wiki/Stellar_classification.md - https://paxabyssi.com/wiki/Brown_dwarf.md - https://paxabyssi.com/wiki/Supergiant.md --- # G-type main-sequence star > Source: https://paxabyssi.com/wiki/G-type_main-sequence_star > > Licence: [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/). Text by Pax Abyssi Wiki contributors; history at https://paxabyssi.com/wiki/G-type_main-sequence_star/history > > Revision 419, 27 September 2026 A **G-type main-sequence star** is a star of spectral class G that is fusing hydrogen into helium in its core. The Sun is one: a G2V star with a surface temperature of 5,772 K [1]. G dwarfs have masses of about 0.9 to 1.1 times the Sun's and surface temperatures of about 5,300 to 6,000 K [2]. They are often called yellow dwarfs, but seen from space they look white with only a faint warm tint [3]. About one star in twenty near the Sun is a G dwarf [4], and because the Sun is one, they are the reference against which every other star, and the search for other Earths, is measured. ## Characteristics ### The G sequence | Type | Temperature (K) | Mass (Sun = 1) | Radius (Sun = 1) | Luminosity (Sun = 1) | B-V | M_V | | ---- | --------------- | -------------- | ---------------- | -------------------- | ---- | ---- | | G0V | 5,930 | 1.06 | 1.10 | 1.35 | 0.60 | 4.48 | | G2V | 5,770 | 1.00 | 1.01 | 1.02 | 0.65 | 4.80 | | G5V | 5,660 | 0.98 | 0.98 | 0.89 | 0.68 | 4.98 | | G9V | 5,380 | 0.90 | 0.85 | 0.55 | 0.78 | 5.55 | Values are the mean main-sequence sequence compiled by Eric Mamajek, building on Pecaut and Mamajek (2013) [2] [5]. A G dwarf's spectrum is dominated by the strong lines of ionised calcium and by the lines of many metals; the hydrogen lines that dominate hotter stars are much weaker. ### The Sun as a G dwarf The International Astronomical Union's nominal solar values, adopted in 2015 as conversion constants, are a radius of 695,700 km, a luminosity of 3.828 × 10²⁶ watts, an effective temperature of 5,772 K and a total solar irradiance at Earth of 1,361 W/m² [1]. The oldest solids in the Solar System, calcium- and aluminium-rich inclusions in meteorites, date to 4,567.3 million years ago, which fixes the Sun's age [6]. Inside, energy travels outward as radiation through the inner 71% of the Sun's radius and by convection above that; helioseismology puts the base of the convection zone at 0.713 solar radii [7]. The convective layer drives the granulation visible on the surface and, with the Sun's rotation, the magnetic field that produces sunspots, flares and the 11-year activity cycle. ![The Sun's full disc in visible light, bright at the centre and darker toward the edge, with a few small dark sunspot groups](https://media.paxabyssi.com/public/48c8bed36d1865d24a8e57138d8ef4142734f71d41c150ab239fa721f8e85bad/2560.webp "Observation: the Sun in visible light from NASA's Solar Dynamics Observatory; the disc darkens toward its edge because we see cooler, higher layers there. Credit: NASA/SDO/HMI/Goddard Space Flight Center.") *Figure 1.* Observation: the Sun in visible light from NASA's Solar Dynamics Observatory; the disc darkens toward its edge because we see cooler, higher layers there. Credit: NASA/SDO/HMI/Goddard Space Flight Center. Licence: Public domain (NASA). ### What colour is the Sun? The Sun's light peaks in the green, but it is spread across all visible wavelengths, and to the eye it adds up to white. Converting model spectra of G2V stars into the colour the eye would see gives a white with the faintest yellow tint [3]. The Sun looks yellow or orange from the ground only because the atmosphere scatters away blue light, most strongly when the Sun is low. ## Evolution A G dwarf brightens slowly as helium accumulates in its core. The Sun began its main-sequence life at about 70% of its present luminosity and is now brightening at about 1% every 110 million years [8]. Models agree on the broad course of what follows and differ in the details [8] [9]: | Stage | Sun's age (billion years) | Luminosity (Sun today = 1) | Radius (Sun today = 1) | | ---------------------------------- | ------------------------- | -------------------------- | ---------------------- | | Arrival on the main sequence | 0 | 0.70 | 0.89 | | Today | 4.58 | 1.00 | 1.00 | | End of the main sequence | 10.0 | 1.84 | 1.37 | | Tip of the red giant branch | 12.17 | 2,730 | 256 (1.2 AU) | | Helium burning begins | 12.17 | 54 | 11 | | Tip of the asymptotic giant branch | 12.30 | about 2,100 to 4,200 | 149 to 179 | (Values from Schröder and Smith 2008.) In that model the Sun loses a third of its mass as a red giant, its planets' orbits widen as a result, and Earth still does not escape: it would need to orbit at about 1.15 AU or more today to survive [8]. An earlier model, with less mass loss, has the red giant Sun reach 170 solar radii, engulf Mercury and spare Venus and Earth [9]. Either way the Sun ends as a white dwarf of about 0.54 solar masses. See [Red giant](https://paxabyssi.com/wiki/Red_giant.md) for this phase. Earlier G types, slightly heavier than the Sun, run through the same sequence faster; later ones, lighter, more slowly. ## Planets around G dwarfs The habitable zone of a G dwarf lies roughly where Earth orbits the Sun: from about 0.95 to 1.68 AU for the Sun itself, using the conservative limits of Kopparapu et al. (2014), shifting inward to about 0.73 to 1.30 AU for a G9 dwarf [10]. The first planet found around a Sun-like star orbited a G dwarf, 51 Pegasi [11]. Kepler-452 b, announced in 2015 as a planet 1.6 times Earth's radius in the habitable zone of a G2 star [12], is a caution about such claims: a later reanalysis found it must still be considered a candidate [13]. The nearest G dwarf, Alpha Centauri A, has a candidate giant planet in its habitable zone imaged by JWST, which awaits confirmation [14]. ## Notable examples | Star | Type | Distance | Notes | | ---------------- | ---- | ----------------- | ----------------------------------------------------------------------------------------------------- | | The Sun | G2V | 1 AU | 1 solar mass, 4.57 billion years old [1] [6] | | Alpha Centauri A | G2V | 1.33 pc (4.34 ly) | 1.079 solar masses, 1.22 solar radii; bound to the K dwarf Alpha Centauri B [15] | | Tau Ceti | G8V | 3.65 pc (11.9 ly) | Four planet candidates from radial velocities [16] | | 18 Scorpii | G2Va | 14.1 pc | A solar twin: 5,823 K and 1.04 solar masses, about 1.6 billion years younger than the Sun [17] [18] | | 51 Pegasi | G2IV | 15.5 pc | Host of the first planet found around a Sun-like star [11] | ![Two bright stars with diffraction spikes close together against a dark sky](https://media.paxabyssi.com/public/bcf60e265c67955f35b8dd7b490de2902da5499c110961a78cb0671619e3162b/1026.webp "Observation: Alpha Centauri A (left), the nearest G dwarf, and its K-type companion Alpha Centauri B, imaged by Hubble. Credit: ESA/Hubble & NASA.") *Figure 2.* Observation: Alpha Centauri A (left), the nearest G dwarf, and its K-type companion Alpha Centauri B, imaged by Hubble. Credit: ESA/Hubble & NASA. Licence: CC BY 4.0. > **In Pax Abyssi** > > G dwarfs are the sim's yellow_dwarf class (code YDW), split into early and late G, each active, moderate or quiet. The game's catalogue holds 23,382 real G-type stars; about half are dwarfs, and most of the rest are giants and subgiants, which a catalogue of visible stars favours. The Sun is included as Sol with its planets and moons at their true positions. Alpha Centauri A, Tau Ceti, 18 Scorpii and 51 Pegasi are catalogue stars at their measured distances. ## See also - [Stellar classification](https://paxabyssi.com/wiki/Stellar_classification.md) - [K-type main-sequence star](https://paxabyssi.com/wiki/K-type_main-sequence_star.md) - [Red dwarf](https://paxabyssi.com/wiki/Red_dwarf.md) - [Red giant](https://paxabyssi.com/wiki/Red_giant.md) - [Sol](https://paxabyssi.com/wiki/Sol.md) - [Habitable zone](https://paxabyssi.com/wiki/Habitable_zone.md) - [White dwarf](https://paxabyssi.com/wiki/White_dwarf.md) ## References 1. Prša, A. et al. (2016). Nominal Values for Selected Solar and Planetary Quantities: IAU 2015 Resolution B3. The Astronomical Journal 152, 41. 2. Mamajek, E. E.. A Modern Mean Dwarf Stellar Color and Effective Temperature Sequence (version 2022.04.16). 3. Harre, J. V. and Heller, R. (2021). Digital color codes of stars. Astronomische Nachrichten 342, 578-587. 4. Reylé, C. et al. (2021). The 10 parsec sample in the Gaia era. Astronomy & Astrophysics 650, A201. 5. Pecaut, M. J. and Mamajek, E. E. (2013). Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-main-sequence Stars. The Astrophysical Journal Supplement Series 208, 9. 6. Connelly, J. N. et al. (2012). The Absolute Chronology and Thermal Processing of Solids in the Solar Protoplanetary Disk. Science 338, 651-655. 7. Basu, S. and Antia, H. M. (1997). Seismic measurement of the depth of the solar convection zone. Monthly Notices of the Royal Astronomical Society 287, 189-198. 8. Schröder, K. P. and Connon Smith, R. (2008). Distant future of the Sun and Earth revisited. Monthly Notices of the Royal Astronomical Society 386, 155-163. 9. Sackmann, I. J., Boothroyd, A. I. and Kraemer, K. E. (1993). Our Sun. III. Present and Future. The Astrophysical Journal 418, 457. 10. Kopparapu, R. K. et al. (2014). Habitable Zones around Main-sequence Stars: Dependence on Planetary Mass. The Astrophysical Journal Letters 787, L29. 11. Mayor, M. and Queloz, D. (1995). A Jupiter-mass companion to a solar-type star. Nature 378, 355-359. 12. Jenkins, J. M. et al. (2015). Discovery and Validation of Kepler-452b: A 1.6 Earth-radius Super Earth Exoplanet in the Habitable Zone of a G2 Star. The Astronomical Journal 150, 56. 13. Mullally, F. et al. (2018). Kepler's Earth-like Planets Should Not Be Confirmed without Independent Detection: The Case of Kepler-452b. The Astronomical Journal 155, 210. 14. Beichman, C. et al. (2025). Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of alpha Centauri A. I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits. The Astrophysical Journal Letters 989, L22. 15. Akeson, R. et al. (2021). Precision Millimeter Astrometry of the alpha Centauri AB System. The Astronomical Journal 162, 14. 16. Feng, F. et al. (2017). Color Difference Makes a Difference: Four Planet Candidates around tau Ceti. The Astronomical Journal 154, 135. 17. Meléndez, J. et al. (2014). 18 Sco: A Solar Twin Rich in Refractory and Neutron-capture Elements. Implications for Chemical Tagging. The Astrophysical Journal 791, 14. 18. Porto de Mello, G. F. and da Silva, L. (1997). HR 6060: The Closest Ever Solar Twin?. The Astrophysical Journal 482, L89-L92. ## Infobox (star class) | Field | Value | | --- | --- | | Code | YDW | | Mass | about 0.90 to 1.06 (G9V to G0V) M_Sun | | Name | G-type main-sequence star | | Image | File:Sun_SDO_HMI_continuum.jpg | | Radius | about 0.85 to 1.10 R_Sun | | Caption | Observation: the Sun in visible light from NASA's Solar Dynamics Observatory, 20 February 2013, with sunspots. Credit: NASA/SDO/HMI/Goddard Space Flight Center | | Activity | Moderate; magnetic cycles like the Sun's 11-year sunspot cycle; more active when young | | Subtypes | YDW-EG early and YDW-LG late G, each active (AC), moderate (MD) or quiet (QT) (sim codes) | | Bv colour | 0.60 (G0V) to 0.78 (G9V); the Sun 0.65 mag | | Luminosity | about 0.55 to 1.35 L_Sun | | Science doc | The sim's yellow dwarf science reference | | Last verified | 2026-09-27, writer B | | Real examples | The Sun (G2V), Alpha Centauri A (G2V), Tau Ceti (G8V), 18 Scorpii (G2Va), 51 Pegasi (G2IV) | | Habitable zone | G0V about 1.09 to 1.92; the Sun 0.95 to 1.68; G9V about 0.73 to 1.30 (conservative, Kopparapu et al. 2014) AU | | Physics engine | Yellow dwarf physics engine and subtype classifier | | Share of stars | About 5% of stars within 10 pc (18 of 337) | | Luminosity class | V | | Perceived colour | White with a faint yellow tint from space; the name 'yellow dwarf' exaggerates it | | Planet occurrence | Planets common; the Sun's family is one of many architectures | | Stellar class key | yellow_dwarf | | Absolute magnitude v | 4.48 (G0V) to 5.55 (G9V); the Sun 4.80 (G2V) mag | | Effective temperature | about 5,300 to 6,000 (G0V 5,930; G2V 5,770; G9V 5,380); the Sun 5,772 K | | Main sequence lifetime | about 10 for the Sun; longer for later G types, shorter for earlier Gyr | | Spectral types covered | G0V to G9V | ## Related pages - [K-type main-sequence star](https://paxabyssi.com/wiki/K-type_main-sequence_star.md): A hydrogen-burning star of spectral class K, between about 0.6 and 0.9 times the Sun's mass, with a surface temperature of about 3,900 to 5,300 K. Often called orange dwarfs, they outnumber Sun-like stars two to one, live for tens of billions of years, and are among the best places to look for habitable planets. - [Red dwarf](https://paxabyssi.com/wiki/Red_dwarf.md): A small, cool, faint main-sequence star of spectral class M, between about 8% and 60% of the Sun's mass. Red dwarfs are about three quarters of all stars, live for trillions of years, flare violently when young, and host many of the nearest known rocky planets. - [Red giant](https://paxabyssi.com/wiki/Red_giant.md): A star in a late stage of life that has run out of hydrogen in its core and swollen to tens or hundreds of times the Sun's size, with a cool, orange-red surface. Stars from about 0.8 to 8 solar masses pass through this stage; the Sun will, in about seven and a half billion years. - [Stellar classification](https://paxabyssi.com/wiki/Stellar_classification.md): How astronomers sort stars by their spectra. A letter (O, B, A, F, G, K, M, and L, T, Y for the coolest objects) and a number give the surface temperature; a Roman numeral gives the size and brightness. The Sun is a G2V star. - [Brown dwarf](https://paxabyssi.com/wiki/Brown_dwarf.md): An object between a planet and a star, roughly 13 to 75 times Jupiter's mass, too light to sustain hydrogen fusion. Brown dwarfs glow with the heat of their formation and cool for ever, passing through the spectral classes L, T and Y; there is about one for every four stars. - [Supergiant](https://paxabyssi.com/wiki/Supergiant.md): A massive star in a late stage of life, tens of thousands to hundreds of thousands of times as luminous as the Sun, of luminosity class I. Red supergiants such as Betelgeuse are among the largest stars known; blue ones such as Rigel are among the brightest. Most end as supernovae within a few million years of forming. Categories: [Stars](https://paxabyssi.com/wiki/Category:Stars.md), [Main-sequence stars](https://paxabyssi.com/wiki/Category:Main-sequence_stars.md), [G-type stars](https://paxabyssi.com/wiki/Category:G-type_stars.md)