--- title: K-type main-sequence star canonical_url: https://paxabyssi.com/wiki/K-type_main-sequence_star markdown_url: https://paxabyssi.com/wiki/K-type_main-sequence_star.md type: wiki-page revision_id: 593 revision_view: stable last_updated: 2026-09-28 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 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. categories: - Stars - Main-sequence stars - K-type stars aliases: - K-type star - K dwarf - K dwarfs - Orange dwarf - Orange dwarfs - K-type main-sequence stars - KV star - ODW - Orange dwarf star infobox: type: star_class code: ODW mass: unit: M_Sun value: about 0.59 to 0.88 source: observed name: K-type main-sequence star image: File:Alpha_Centauri_AB_Hubble_potw1635a.jpg radius: unit: R_Sun value: about 0.61 to 0.81 source: observed caption: "Observation: Alpha Centauri A (left) and the K dwarf Alpha Centauri B (right), imaged by Hubble. Credit: ESA/Hubble & NASA" activity: Moderate; less flare activity than red dwarfs, more than the Sun when young subtypes: ODW-EK early, ODW-MK mid and ODW-LK late K, each active (AC), moderate (MD) or quiet (QT) (sim codes) bv_colour: unit: mag value: 0.82 (K0V) to 1.40 (K9V) source: observed luminosity: unit: L_Sun value: about 0.08 to 0.46 source: observed science_doc: The sim's orange dwarf science reference last_verified: 2026-09-27, writer B real_examples: Alpha Centauri B (K1V), epsilon Eridani (K2V), 61 Cygni A and B (K5V, K7V), epsilon Indi A (K5V) habitable_zone: unit: AU value: K0V about 0.66 to 1.19; K5V about 0.42 to 0.79; K9V about 0.32 to 0.60 (conservative, Kopparapu et al. 2014) source: model physics_engine: Orange dwarf physics engine and subtype classifier share_of_stars: About 11% of stars within 10 pc (38 of 337) luminosity_class: V perceived_colour: Pale orange; close to a blackbody of the same temperature planet_occurrence: Planets common; epsilon Eridani and epsilon Indi A host giant planets stellar_class_key: orange_dwarf absolute_magnitude_v: unit: mag value: 5.78 (K0V) to 8.56 (K9V) source: observed effective_temperature: unit: K value: about 3,900 to 5,300 (K0V 5,270; K5V 4,440; K9V 3,930) source: observed main_sequence_lifetime: unit: Gyr value: roughly 15 to 20 for K0V and 30 to 40 for K5V (scaling estimates) source: model spectral_types_covered: K0V to K9V related: - https://paxabyssi.com/wiki/G-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 --- # K-type main-sequence star > Source: https://paxabyssi.com/wiki/K-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/K-type_main-sequence_star/history > > Revision 593, 28 September 2026 A **K-type main-sequence star** is a star of spectral class K that is fusing hydrogen in its core: smaller, cooler and fainter than the Sun, but larger and brighter than a red dwarf. K dwarfs have between about 0.6 and 0.9 times the Sun's mass, surface temperatures of about 3,900 to 5,300 K, and between a tenth and a half of the Sun's luminosity [1]. They are often called orange dwarfs, and to the eye they are a pale orange [2]. Near the Sun they are about twice as common as G dwarfs [3], and because they are long-lived, steady and bright enough to warm a planet at a comfortable distance, many astronomers regard them as the most promising homes for life beyond the Solar System [4]. ## Characteristics | Type | Temperature (K) | Mass (Sun = 1) | Radius (Sun = 1) | Luminosity (Sun = 1) | B-V | M_V | | ---- | --------------- | -------------- | ---------------- | -------------------- | ---- | ---- | | K0V | 5,270 | 0.88 | 0.81 | 0.46 | 0.82 | 5.78 | | K2V | 5,100 | 0.82 | 0.78 | 0.37 | 0.88 | 6.07 | | K5V | 4,440 | 0.70 | 0.70 | 0.17 | 1.15 | 7.28 | | K7V | 4,100 | 0.64 | 0.63 | 0.10 | 1.34 | 8.16 | | K9V | 3,930 | 0.59 | 0.61 | 0.08 | 1.40 | 8.56 | Values are from Eric Mamajek's compilation of mean main-sequence properties, building on Pecaut and Mamajek (2013) [1] [5]. A K dwarf's spectrum shows strong lines of neutral metals such as iron, calcium and sodium, and toward the late K types the first molecular bands appear. Like the Sun, K dwarfs have a radiative core wrapped in a convective envelope, and they have magnetic cycles and starspots; young K dwarfs are more active than the Sun and flare, though less violently, relative to their size, than red dwarfs. ## Long, steady lives A star's lifetime on the main sequence grows steeply as its mass falls, roughly as the inverse third to fourth power of the mass for stars like these [6]. That puts a K0 dwarf's main-sequence life at roughly 15 to 20 billion years and a K5 dwarf's at 30 to 40 billion, estimates from the scaling rather than from detailed models. Either way it is longer than the present age of the universe, 13.8 billion years: only stars heavier than about 0.8 solar masses have yet had time to leave the main sequence [6], so every K dwarf ever formed is still a K dwarf, apart from a few of the heaviest. A K dwarf also brightens more slowly than the Sun, so its habitable zone drifts outward more slowly. Cuntz and Guinan (2016) estimated how long a planet could stay within the conservative habitable zone as its star ages: about 16 billion years around a K0 dwarf and 30 billion around a K5, against about 5 billion for a G2 star like the Sun. Weighing that against the higher ultraviolet and flare output of the smaller M dwarfs, they found late G to mid K stars the most promising hosts for life, with early K dwarfs at the top [4]. ## The habitable zone K dwarfs' habitable zones are closer in than the Sun's but not so close that planets there are certain to be tidally locked: about 0.66 to 1.19 AU for a K0 dwarf and about 0.42 to 0.79 AU for a K5, using the conservative limits of Kopparapu et al. (2014) [7]. See [Habitable zone](https://paxabyssi.com/wiki/Habitable_zone.md) for how these edges are set. (Image pending: Four horizontal bars on a shared distance scale showing the habitable zones of a Sun-like star, two K dwarfs and an M dwarf, moving inward and narrowing with the star's temperature) *Figure 1.* Diagram: conservative habitable zones of G2, K0, K5 and M0 dwarfs on one scale, from Kopparapu et al. (2014). ## How we know Several K dwarfs are among the Sun's nearest neighbours, and one of them was the first star beyond the Sun to have its distance measured. In 1838 Friedrich Bessel reported the parallax of 61 Cygni, a pair of K dwarfs, the tiny annual shift in its position as Earth orbits the Sun [8]. Today the masses of K dwarfs come from binary orbits such as that of Alpha Centauri B around A [9], and their radii from interferometry. ## Notable examples | Star | Type | Distance | Notes | | ---------------- | -------- | ----------------- | ------------------------------------------------------------------------------- | | Alpha Centauri B | K1V | 1.33 pc (4.34 ly) | 0.909 solar masses, 0.859 solar radii; orbits the G dwarf Alpha Centauri A [9] | | Epsilon Eridani | K2V | 3.22 pc (10.5 ly) | Giant planet of 0.78 Jupiter masses at 3.5 AU on a 7.4-year orbit [10] [11] | | 61 Cygni A and B | K5V, K7V | 3.50 pc (11.4 ly) | First star with a measured parallax, 1838 [8] | | Epsilon Indi A | K5V | 3.6 pc (12 ly) | Its cold giant planet, epsilon Indi Ab, was imaged by JWST [12] | Epsilon Eridani's planet, first reported from the star's wobble in 2000 [10], was confirmed with a combination of radial velocities and direct-imaging limits, which pinned its mass and orbit [11]. ![Artist's concept of an orange star surrounded by dusty rings, with a giant planet in the foreground](https://media.paxabyssi.com/public/02f18b444e35292c5a89cbcc7e115ad7b477b67833ae9e5c049f4b8b26bc796a/2560.webp "Artist's concept: the young K dwarf epsilon Eridani with its belts of dust and a giant planet. Credit: NASA/JPL-Caltech.") *Figure 2.* Artist's concept: the young K dwarf epsilon Eridani with its belts of dust and a giant planet. Credit: NASA/JPL-Caltech. Licence: Public domain (NASA). ## In Pax Abyssi K dwarfs are the simulation's orange dwarf class (code ODW), split into early, mid and late K by temperature, each active, moderate or quiet. The game's catalogue holds 33,053 real K-type stars, the largest group in it, but most are K giants: bright enough to be seen from far away, they dominate any catalogue of visible stars, and about 5,000 of the catalogue's K stars are dwarfs. Alpha Centauri B (Toliman), epsilon Eridani (Ran), 61 Cygni and epsilon Indi sit at their measured distances, and each is a system you can fly to. Of the 38 K dwarfs in the flyable set, 27 have generated planets, 142 in all, and their systems run compact: tidally locked lava worlds are the commonest type, and eleven are dry habitable worlds. The generated galaxy, arriving next, draws about one star in eight from the K dwarf class. Up close, a K dwarf is orange, its face broken into large granulation cells with strong contrast and frequent spots, and its limb darkened by the coefficient for the class, 0.70. Under the default SCIENTIFIC sun palette it takes the true colour of its light, a pale orange; the pictures here use the GAME palette, which paints it a deeper orange. Both are choices of the **sun palette** row in Esc > Options > SPACE. ![An orange star filling the frame, its face streaked with dark lanes between bright cells](https://media.paxabyssi.com/public/5be7f65e3c25f8aaf1fa7a18b1f413e2b892dc4c6757c364e83e0fa3117b78c3/900.webp "In Pax Abyssi: a 4,500 K orange dwarf filling the view, under the GAME sun palette.") *Figure 3.* In Pax Abyssi: a 4,500 K orange dwarf filling the view, under the GAME sun palette. ![A small orange disc in a black sky, with two bright points of light just to its right](https://media.paxabyssi.com/public/87b3473794d43dd132e162c3490a6668849f80464ea59b35dc51683c89f9ba40/1000.webp "In Pax Abyssi: the same 4,500 K star from 8.9 stellar radii, a small orange disc among the stars.") *Figure 4.* In Pax Abyssi: the same 4,500 K star from 8.9 stellar radii, a small orange disc among the stars. ## See also - [Stellar classification](https://paxabyssi.com/wiki/Stellar_classification.md) - [G-type main-sequence star](https://paxabyssi.com/wiki/G-type_main-sequence_star.md) - [Red dwarf](https://paxabyssi.com/wiki/Red_dwarf.md) - [Habitable zone](https://paxabyssi.com/wiki/Habitable_zone.md) - [Red giant](https://paxabyssi.com/wiki/Red_giant.md) - [Planet occurrence](https://paxabyssi.com/wiki/Planet_occurrence.md) ## References 1. Mamajek, E. E.. A Modern Mean Dwarf Stellar Color and Effective Temperature Sequence (version 2022.04.16). 2. Harre, J. V. and Heller, R. (2021). Digital color codes of stars. Astronomische Nachrichten 342, 578-587. 3. Reylé, C. et al. (2021). The 10 parsec sample in the Gaia era. Astronomy & Astrophysics 650, A201. 4. Cuntz, M. and Guinan, E. F. (2016). About Exobiology: The Case for Dwarf K Stars. The Astrophysical Journal 827, 79. 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. Adams, F. C. and Laughlin, G. (1997). A dying universe: the long-term fate and evolution of astrophysical objects. Reviews of Modern Physics 69, 337-372. 7. Kopparapu, R. K. et al. (2014). Habitable Zones around Main-sequence Stars: Dependence on Planetary Mass. The Astrophysical Journal Letters 787, L29. 8. Bessel, F. W. (1838). A letter from Professor Bessel to Sir J. Herschel, Bart., dated Konigsberg, Oct. 23, 1838. Monthly Notices of the Royal Astronomical Society 4, 152-161. 9. Akeson, R. et al. (2021). Precision Millimeter Astrometry of the alpha Centauri AB System. The Astronomical Journal 162, 14. 10. Hatzes, A. P. et al. (2000). Evidence for a Long-Period Planet Orbiting epsilon Eridani. The Astrophysical Journal 544, L145-L148. 11. Mawet, D. et al. (2019). Deep Exploration of epsilon Eridani with Keck Ms-band Vortex Coronagraphy and Radial Velocities: Mass and Orbital Parameters of the Giant Exoplanet. The Astronomical Journal 157, 33. 12. Matthews, E. C. et al. (2024). A temperate super-Jupiter imaged with JWST in the mid-infrared. Nature 633, 789-792. ## Infobox (star class) | Field | Value | | --- | --- | | Code | ODW | | Mass | about 0.59 to 0.88 M_Sun | | Name | K-type main-sequence star | | Image | File:Alpha_Centauri_AB_Hubble_potw1635a.jpg | | Radius | about 0.61 to 0.81 R_Sun | | Caption | Observation: Alpha Centauri A (left) and the K dwarf Alpha Centauri B (right), imaged by Hubble. Credit: ESA/Hubble & NASA | | Activity | Moderate; less flare activity than red dwarfs, more than the Sun when young | | Subtypes | ODW-EK early, ODW-MK mid and ODW-LK late K, each active (AC), moderate (MD) or quiet (QT) (sim codes) | | Bv colour | 0.82 (K0V) to 1.40 (K9V) mag | | Luminosity | about 0.08 to 0.46 L_Sun | | Science doc | The sim's orange dwarf science reference | | Last verified | 2026-09-27, writer B | | Real examples | Alpha Centauri B (K1V), epsilon Eridani (K2V), 61 Cygni A and B (K5V, K7V), epsilon Indi A (K5V) | | Habitable zone | K0V about 0.66 to 1.19; K5V about 0.42 to 0.79; K9V about 0.32 to 0.60 (conservative, Kopparapu et al. 2014) AU | | Physics engine | Orange dwarf physics engine and subtype classifier | | Share of stars | About 11% of stars within 10 pc (38 of 337) | | Luminosity class | V | | Perceived colour | Pale orange; close to a blackbody of the same temperature | | Planet occurrence | Planets common; epsilon Eridani and epsilon Indi A host giant planets | | Stellar class key | orange_dwarf | | Absolute magnitude v | 5.78 (K0V) to 8.56 (K9V) mag | | Effective temperature | about 3,900 to 5,300 (K0V 5,270; K5V 4,440; K9V 3,930) K | | Main sequence lifetime | roughly 15 to 20 for K0V and 30 to 40 for K5V (scaling estimates) Gyr | | Spectral types covered | K0V to K9V | ## Related pages - [G-type main-sequence star](https://paxabyssi.com/wiki/G-type_main-sequence_star.md): 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. - [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), [K-type stars](https://paxabyssi.com/wiki/Category:K-type_stars.md)