Object Name: Messier 103
Alternative Designations: M103, NGC 581
Object Type: Type D Open Cluster
Constellation: Cassiopeia
Right Ascension: 01 : 33.2 (h:m)
Declination: +60 : 42 (deg:m)
Distance: 8.5 (kly)
Visual Brightness: 7.4 (mag)
Apparent Dimension: 6.0 (arc min)
Locating Messier 103: Locating M103 is fairly easy even under moderately light polluted conditions. Simply identify Delta Cassiopeiae (Ruchbah), a bright, blue-white star that marks one of the lower positions of Cassiopeia’s class “W” asterism. Simply center it in the finderscope and look about 1/2 a degree north and 1 degree east in the direction of Epsilon. In binoculars and a finderscope it will appear as a diamond shape patch of nebulosity which tries to resolve and will reveal its individual stars to even a small telescope. Loosely constructed, M103 makes a wonderful target for urban skies and less than perfect sky conditions.
History: This sparkling open cluster was discovered by Pierre Mechain in either March or April of 1781and added by Charles Messier to his catalog before he had a chance to observe it. From Mechain’s notes: “Cluster of stars between Epsilon and Delta of the leg of Cassiopeia.”
Sir William Herschel would capture it again on August 8, 1783 when he describes: “14 or 16 pL. [pretty large (bright)] stars with a great many eS. [extremely small (faint)] ones. Two of the large [bright] ones are double, one of the 1st the other of the 2nd class. (*) The compound eye glass shews a few more that may be taken into the cluster so as to make them about 20. I exclude a good many straggling ones, otherwise there would be no knowing where to stop.”
Look for the colors and enjoy your observations!
Top M103 image credit, Palomar Observatory courtesy of Caltech, M103 – Roberto Mura – Wikipedia Image, M103 2MASS image and M103 image courtesy of NOAO/AURA/NSF.
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