Delta Ursae Majoris is a star of apparent magnitude of +3.32 in Ursa Major, making it the dimmest of the seven stars in the Big Dipper. It links the Dipper's handle to its bowl, and in the bigger picture links Ursa Major's tail to the Bear's hindquarters. It has the traditional name Megrez, which comes from a long Arabic phrase that means the "root of the Great Bear's tail".
Properties
This rather ordinary, white class A3 V hydrogen-fusing star glows with a surface temperature of 8630 K. From its distance of 81 light years, it has a luminosity of 23 suns, a radius double the Sun's, and contains about two solar masses. Like the middle five stars of the Dipper, Megrez is part of the sprawling Ursa Major moving group, all moving through space together at about the same distance.
Megrez and the other central Dipper stars are about 50 million years old, roughly half of the star's hydrogen-fusing lifetime. Megrez has been searched for a surrounding dust disk of the kind found around Vega and Fomalhaut (from which planets might presumably have formed), but nothing has been found. Megrez has also been accused of fading over the centuries, as Tycho Brahe recorded it second magnitude; but this is most likely false.
Megrez has two faint optical (line-of-sight) companions: the 11th magnitude δ UMa B, 190" away; and the 10th magnitude δ UMa C, 186" away.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]