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 57277 HIP 57282 HIP 57284 HIP 85859 HIP 8586 HIP 85864 HIP 85891 HIP 85892 HIP 85930 HIP 85982 HIP 86000 HIP 80280 HIP 57309 HIP 57310 HIP 31052 HIP 31056 HIP 31084 HIP 31085 HIP 31102 HIP 78122 HIP 78153 HIP 78157 HIP 78162 HIP 78164 HIP 57343 HIP 87892 HIP 87898 HIP 87912 HIP 87934 HIP 87951 HIP 87975 HIP 88031 HIP 78170 HIP 78171 HIP 78175 HIP 78176 HIP 78178 HIP 78182 HIP 78194 HIP 86224 HIP 57419 HIP 34266 HIP 34268 HIP 34269 HIP 990 HIP 99043 HIP 88206 HIP 88232

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