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 39702 HIP 39703 HIP 39709 HIP 51716 HIP 70966 HIP 48901 HIP 48902 HIP 48905 HIP 48907 HIP 48912 HIP 48918 HIP 48919 HIP 48921 HIP 48927 HIP 48929 HIP 28297 HIP 28316 HIP 28332 HIP 28335 HIP 28339 HIP 2834 HIP 28341 HIP 28344 HIP 3987 HIP 3998 HIP 4002 HIP 4003 HIP 401 HIP 4010 HIP 4014 HIP 51724 HIP 51728 HIP 5173 HIP 39763 HIP 4020 HIP 51731 HIP 51732 HIP 51738 HIP 51742 HIP 68662 HIP 51745 HIP 51747 HIP 51748 HIP 5175 HIP 51750 HIP 51752 HIP 51753 HIP 38404

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