Unlike most deep-sky objects, this one is obvious to the unaided eye. The Coma Star Cluster is so big it barely squeezes into the frame of the wide field telescope I used to take this image. To see it for yourself just look up and due south on northern spring evenings. To the left of Leo, off his back end, shines this loose and scattered grouping of stars obvious to the unaided eye on a dark night. Indeed, I think in olden times this bunch of stars was drawn as the tuft of hair at the end of Leo’s tail.
But now we picture this cluster of stars as the tresses of hair of the late dynasty Egyptian Queen Berenice II, placed in the sky to honour her loyalty to her husband, the Pharaoh Ptolemy. The story has it that the group did not become officially recognized as a constellation until the 16th century.
The constellation of Coma Berenices (hair of Berenices) extends over a larger area of sky than just this grouping, but the Coma star cluster is certainly the most obvious feature of the constellation. Binoculars frame it well (taking in a bit more sky than this image) and are the best way to view it. With their narrow field, telescopes look right through this object.
The cluster is spread over nearly five degrees of sky and contains about 40 stars, so a rather sparse gathering to be sure. Many open clusters, like M67 pictured a couple of blogs back, contain hundreds of stars. Coma is so big in our sky because it is one of the closest star clusters to us, only 288 light years away, and above us toward the north pole of our Galaxy.
Its size and scattered appearance actually meant it hid in plain sight for centuries – yes, it was given a name and people saw it, but astronomers didn’t give it status as an official star cluster until 1938. In 1915 astronomer P.J. Melotte had listed it as object number 111 in his catalogue of star groupings. And so today, we usually refer to this cluster as Mel 111, the most famous entry in “Mel’s” catalog!
I took this shot with the same gear used for the M67 and Beehive M44 shots earlier, so it’s easy to see just how much bigger the Coma Cluster is than just about every other star cluster in the sky. This is a stack of four 6-minute exposures at ISO 1600 with the Canon 7D camera and the 92mm TMB apo refractor.
– Alan, April 2011 / Image © 2011 Alan Dyer