Class K — K-type (Orange)

K-type stars are orange main-sequence stars with surface temperatures of 3,700 to 5,200 K. They are relatively common, making up about 12% of main-sequence stars. K-type stars are increasingly considered prime candidates in the search for habitable exoplanets — they are stable, long-lived (15-30 billion years), and less prone to stellar flares than M dwarfs. Notable examples include Arcturus (K1.5IIIFe-0.5), the brightest star in the northern hemisphere, and Epsilon Eridani (K2V).

K-type stars are orange stars with surface temperatures between 3,700 and 5,200 K, comprising about 12.1% of main-sequence stars. They have emerged as increasingly attractive targets in exoplanet habitability studies: their habitable zones are closer-in than the Sun's (making transiting planets easier to detect), they are less active than M dwarfs (reducing atmospheric stripping of orbiting planets), and their main-sequence lifetimes of 15-30 billion years exceed the current age of the universe — offering exceptionally stable environments.

Characteristics

K-type spectra show strong neutral metal lines (iron, calcium, sodium) and the beginnings of molecular absorption bands (TiO) in the coolest K-types. Their deep convective envelopes drive moderate magnetic activity with well-defined starspot cycles. K dwarfs are less variable than M dwarfs, avoiding the violent flare activity that may sterilize planets around red dwarfs. With masses of 0.45-0.8 solar masses and luminosities of 0.08-0.6 solar, K dwarfs are sometimes called 'Goldilocks stars' — not too hot, not too cool, not too variable for life.

Notable Examples

Arcturus (Alpha Bootis, K1.5III) is the brightest star in the northern celestial hemisphere and a K-type giant 25 times the Sun's diameter, whose orange color is immediately apparent. Aldebaran (Alpha Tauri, K5III), the Eye of the Bull, is another prominent orange giant 44 times solar diameter. Epsilon Eridani (K2V) at 10.5 light-years is one of the nearest stars known to host a confirmed exoplanet and a debris disk. Alpha Centauri B (K1V) is the secondary component of our nearest stellar system.

HIP 24001HIP 24014HIP 2402HIP 24023HIP 27314HIP 27315HIP 27317HIP 27319HIP 27320HIP 27325HIP 27326HIP 27329HIP 51017HIP 51019HIP 51020HIP 51021HIP 51022HIP 24038HIP 2404HIP 24041HIP 24044HIP 24050HIP 24054HIP 24056HIP 4818HIP 48180HIP 48184HIP 48187HIP 48191HIP 48192HIP 48193HIP 48200HIP 42589HIP 24068HIP 24070HIP 24077HIP 24085HIP 24086HIP 24087HIP 24090HIP 27382HIP 27383HIP 27384HIP 27387HIP 27389HIP 27393HIP 27399HIP 2740

Frequently Asked Questions

What is a class K star?
Class K (K-type (Orange)) stars are orange stars. K-type stars are orange main-sequence stars with surface temperatures of 3,700 to 5,200 K. They are relatively common, making up about 12% of main-sequence stars. K-type stars are increasingly conside
How hot are class K stars?
Class K stars have surface temperatures between 3,700 K and 5,200 K.
What color are class K stars?
Class K stars appear orange.
How many class K stars are in the StarFYI database?
StarFYI currently catalogs 32,180 class K stars.
How luminous are class K stars?
Dim, 0.08-0.6 solar luminosities