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 69240 HIP 69241 HIP 69242 HIP 6925 HIP 48362 HIP 48363 HIP 71521 HIP 71524 HIP 71537 HIP 71539 HIP 69253 HIP 69254 HIP 69258 HIP 69260 HIP 69263 HIP 69268 HIP 69271 HIP 69273 HIP 69277 HIP 69279 HIP 48427 HIP 32852 HIP 32855 HIP 32919 HIP 55965 HIP 55969 HIP 84872 HIP 71544 HIP 71545 HIP 7155 HIP 71553 HIP 71554 HIP 7156 HIP 71567 HIP 48460 HIP 48463 HIP 69294 HIP 69297 HIP 6930 HIP 69301 HIP 69303 HIP 69305 HIP 71570 HIP 71571 HIP 71576 HIP 71580 HIP 71591 HIP 86874

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