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 24559HIP 24562HIP 24563HIP 27845HIP 69841HIP 69846HIP 24568HIP 24572HIP 24577HIP 24582HIP 24583HIP 24586HIP 24593HIP 24595HIP 67489HIP 6749HIP 67491HIP 67492HIP 6750HIP 67501HIP 67503HIP 67504HIP 67531HIP 67533HIP 67537HIP 246HIP 24610HIP 24614HIP 24622HIP 24623HIP 24624HIP 27918HIP 27920HIP 69865HIP 97029HIP 97047HIP 24628HIP 24631HIP 24633HIP 24638HIP 24644HIP 24646HIP 24650HIP 8324HIP 69877HIP 69879HIP 69885HIP 69889

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