This field in Cassiopeia holds several interesting open clusters, including Messier 103, and NGC 663. Hold your mouse cursor over the image to see object identifications.

Open clusters are collections of gravitationally bound stars that formed out of the same cloud of interstellar gas and dust.

M103, the 103rd, and last object on Charles Messier's original list of objects that were not comets, was discovered by Pierre Méchain in 1781. It is 25 million years old and located 8,500 light-years away. It is located 1 degree northeast of Ruchbah (Delta Cassiopeiae).

The brightest star which appears to be a member of M103 is Struve 131 (HD 9311), a double star at the northwest corner of the cluster with the primary being magnitude 7.3 and the companion magnitude 10.5. It is not a true member of the cluster however, it just happens to lie along the same line of sight. M103 is 6 arcminutes in diameter and shines at magnitude 7 and is comprised of 40 to 170 members, depending on the source counting the stars. A magnitude 10.8 red-giant star can also be seen in the cluster.

NGC 663 is the largest and most prominent open cluster in the image, just to the left of center. It has an apparent size of 16 arcminutes and shines at magnitude 7.1. It can be found 1.5 degrees east-northeast of M103.

IC 166, at upper left, is 7 arcminutes in diameter and magnitude 11.7. It is located 13,000 light-years away and appears dimmed and reddened by dust in the plane of the Milky Way. It is thought to be 1 billion years old.

Other clusters in the image are Berkley 6, NGC 659, NGC 654, Trumpler 1, and Czernik 4.

North is to the top in the above image.

Messier 103 Catalogs: M103, NGC 581 Object Type: Open Cluster Magnitude: 7.4v Size: 6' Constellation: Cassiopeia Image Field Centered At: RA: 01h 43m 02s Dec: +61° 17' 04"