Alioth (Epsilon Ursae Majoris)


Alioth (Epsilon Ursae Majoris) is the brightest star in the constellation Ursa Major and the third star from the end of the Big Dipper's handle; its proper name comes from a corruption of the Arabic for "black horse."


Alioth is the brightest Ap star and is also an Alpha2 Canum Venaticorum star with a period of 5.1 days. Its oxygen abundance is 100,000 times greater near the magnetic equator than near the magnetic poles (which are displaced from the rotational equator and poles); the amount of chromium varies similarly. Though visually the brightest Ap star, Alioth has one of the weakest magnetic fields of this class – 15 times weaker than that observed for Cor Caroli.


visual magnitude 1.76
absolute magnitude -0.22
spectral type A0V
surface temperature 9,400 K
luminosity 108 Lsun
mass about 3 Msun
distance 81 light-years (25 pc)
position RA 12h 54m 01.7s,
Dec +55° 57' 35"
other designations Aliath, 77 Ursae Majoris,
HR 4905, BD +56°1627,
HD 112185, GCTP 2964.00,
SAO 28553, FK5 483,
CCDM 12540+5558, HIP 62956