Gamma Ursae Minoris glows at magnitude +3.00 in the bowl of the Little Dipper, and is circumpolar from anywhere north of 20° north latitude. Third brightest within Ursa Minor, the Smaller Bear, it also has the common name Pherkad. The name derives from the Arabic for "the two calves," which originally referred to both Kochab (β UMi) and Pherkad. Together, these two stars are also called "the Guardians of the Pole".
Properties
Pherkad is a hot class A3 Iab giant star, with a temperature of 8600 K. With a distance of 480 light years, it has a luminosity 1100 times the Sun's, and a radius 15 times solar. The star is evolving, with a quiet helium core surrounded by a shell of fusing hydrogen; its current temperature and luminosity suggest a mass of around five suns. If that is the case, it left the hydrogen-fusing main sequence only about 100 million years ago, and before long will turn into a red giant star much like Kochab is today. Though evolved, Pherkad is still spinning rapidly, over 170 km/sec at the equator.
Pherkad is a slightly variable star, changing less than a tenth of a magnitude with a period of only a couple hours. No one seems to know how to classify it; it was also once classified as "shell star," with a surrounding ring of gas, but that seems to have disappeared as well.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]