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 109351 HIP 109353 HIP 109357 HIP 10936 HIP 113089 HIP 113091 HIP 113095 HIP 113097 HIP 113103 HIP 113104 HIP 113105 HIP 113108 HIP 113116 HIP 113121 HIP 113123 HIP 13886 HIP 113125 HIP 113128 HIP 113129 HIP 113130 HIP 113141 HIP 113143 HIP 113144 HIP 109365 HIP 109366 HIP 109368 HIP 109370 HIP 109387 HIP 109392 HIP 113154 HIP 11316 HIP 113160 HIP 113169 HIP 11317 HIP 109397 HIP 109399 HIP 109402 HIP 109403 HIP 109406 HIP 109407 HIP 109408 HIP 10941 HIP 109415 HIP 10942 HIP 109421 HIP 13887 HIP 113180 HIP 113184

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