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 109075HIP 109088HIP 10909HIP 109092HIP 109094HIP 109096HIP 1091HIP 109100HIP 109102HIP 109103HIP 109108HIP 10911HIP 109114HIP 109123HIP 109126HIP 109128HIP 109131HIP 109132HIP 109134HIP 109140HIP 109148HIP 109149HIP 109154HIP 109163HIP 109164HIP 109166HIP 10917HIP 109170HIP 109174HIP 109175HIP 109178HIP 109179HIP 109183HIP 109184HIP 109187HIP 109188HIP 10919HIP 10920HIP 109204HIP 10921HIP 109213HIP 109219HIP 109222HIP 109223HIP 109225HIP 109226HIP 109228HIP 109229

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