Delta Ursae Minoris - Yildun

At magnitude +4.35, Delta Ursae Minoris is the sixth brightest star in Ursa Minor, the Smaller Bear. One of the faint stars of the Little Dipper's handle, it cannot be seen with the naked eye from any modestly lit town. It has the traditional name Yildun (or Vildiur, or Gildun), taken from a Turkish word for "star."

Why such a faint star was given such a singular proper name is not known, but it may have to do with its position. Yildun is only 3.5° away from the North Celestial Pole. It is circumpolar - perpetually visible - from the entire northern hemisphere. If not for Polaris, Yildun would make a reasonably acceptable Pole star, and is the second-closest star to the Pole with a proper name. Moreover, Yildun is about as close to the pole as it can be, since precession, the 26,000-year wobble of the Earth's axis, is now carrying the pole away from it.

Properties

Physically, Yildun is an ordinary white class A1 V main-sequence star 183 light years away. It has a temperature of 9000 K, a luminosity of 47 suns, and a diameter 2.8 times solar. Its only real distinction is a high rotation speed of 174 km/sec, that gives it a rotation period of just 19 hours.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]