On a clear winter night, a small patch of light can be associated with Alpha (Mirfak) and Delta Persei. This brightening of the Milky Way can be seen with the naked eye. A pair of binoculars will reveal an interesting star field between Alpha and Delta Persei. This group of stars is also called the Per OB3 association or the Alpha Persei Moving Group. It was catalogued in 1915 by the British astronomer Philibert Jacques Melotte as the 20th entry in his catalogue of open star clusters. Mel 20 is a large and bright object. At a distance of 540 l-y, it is not much farther away than the Pleiades. Its size of almost 4Â° makes it the perfect binocular object, even for light polluted skies. I observed Mel 20 with the first quarter moon nearby. Melotte 20 reminds me of a snake, Alpha Persei being the head and Delta the tail. The sketch shows only the core of the cluster. A total of 100 stars are believed to be true group members. Many outlying members of the group are just too spread out to be seen in a single field of view.
Site : Bekkevoort, Belgium ( 51Â° N )
Date : December 7, 2008
Time : around 20.45UT
Binoculars : Bresser Spezial-Jagd 8x56
Filter : none
Mount : Trico Machine Sky Window
Seeing : 3/5
Transp. : 3/5
Sky brightness : 18.98 magnitudes per square arc second near zenith (SQM reading).
Sketch Orientation: N up, W right.
Digital sketch made with Corel Paint Shop Pro X2, based on a raw pencil sketch.
(Note: if the sketch does look too dark on your monitor, try to darken the room.)