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 114272HIP 114275HIP 114278HIP 114279HIP 11428HIP 117973HIP 117978HIP 117979HIP 11798HIP 117988HIP 11799HIP 117992HIP 117993HIP 117995HIP 117999HIP 114286HIP 114288HIP 114292HIP 114297HIP 114298HIP 114306HIP 114307HIP 114308HIP 11431HIP 11800HIP 118003HIP 118008HIP 118009HIP 118014HIP 118016HIP 11802HIP 118024HIP 114310HIP 114314HIP 114316HIP 114321HIP 114323HIP 114324HIP 11433HIP 114331HIP 114335HIP 114337HIP 11434HIP 118028HIP 11803HIP 118034HIP 118035HIP 118036

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