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 46185 HIP 46186 HIP 46187 HIP 46190 HIP 43263 HIP 43270 HIP 43272 HIP 43280 HIP 43284 HIP 43289 HIP 43293 HIP 46197 HIP 46198 HIP 46199 HIP 4620 HIP 46203 HIP 46204 HIP 46207 HIP 46209 HIP 46210 HIP 46212 HIP 46214 HIP 433 HIP 43307 HIP 43309 HIP 43310 HIP 43312 HIP 60170 HIP 57500 HIP 57512 HIP 57513 HIP 43375 HIP 43390 HIP 43404 HIP 43516 HIP 46254 HIP 46270 HIP 46276 HIP 46281 HIP 46288 HIP 46315 HIP 46338 HIP 46343 HIP 46374 HIP 46473 HIP 46496 HIP 46532 HIP 46545

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