Kochab (Beta Ursae Minoris)


Ursa Minor, with Kochab labeled.

Kochab (Beta Ursae Minoris) is the second brightest star in the constellation Ursa Minor, marking the top and front of the Little Dipper. Its Arabic name (also given as Kocab) is obscure and may simply mean 'star.' Together with the other bowl star, Pherkad (Gamma UMi), they make the Guardians of the Pole. Polaris is only a temporary pole star that will get better into the next century and then will begin to shift away. About the year 1100 BC, the pole made a reasonably close pass to Kochab, and there are old references to this star being called 'Polaris.'


Kochab has exhausted its core supply of hydrogen and is an evolving orange giant star probably at the stage of helium-burning. It is also classified as a mild barium star.


visual magnitude 2.07
absolute magnitude -0.88
spectral type K4IIIBa0.3
surface temperature 4,000 K
luminosity 500 Lsun
radius 50 Rsun
distance 126 ± 3 light-years (38.8 ± 0.8 pc)
position RA 14h 50m 42.3s,
Dec +74° 9' 20"
other designations Kocab, Kochah, 7 Ursae Minoris,
HR 5563, BD +74 595, HD 131873,
GCTP 3373.00, SAO 8102, FK5 550,
HIP 72607