NGC 4755, Caldwell 94, Melotte 114, Kappa Crucis Cluster, Jewel Box

Open Cluster

Crux

RA: 12 53 39.6
DEC: -60 22 16

Mag: 4.2
Diam: 10.3’ x 10.3’

Sorry for the rather short article this week.

The Jewel Box cluster often is hailed as one of the most beautiful open clusters in the southern, or even the entire, sky. It was discovered by Nicolas de Lacaille in 1751 or 1752 from South Africa. The cluster already is visible to the naked eye and Lacaille saw it as a nebulous cluster in his 12 mm (yes, that’s not a typo) telescope. The famous name "Jewel Box" comes from John Herschel who compared the cluster to a fancy piece of jewellery. The same John Herschel recorded the positions of just over 100 members between 1834 and 1838.

eso0940a.jpg
Credit: ESO

The brightest stars in the cluster are between magnitudes 5.8 and 7.8 and form a characteristic asterism shaped like a letter A. All of them are B-type stars except one which lies almost exactly in the center of the A and is an M2 red supergiant named DU Crucis. Like DU Crucis, many of the B-type stars are variable, some with a very small and others with a somewhat larger amplitude. One of the bright stars is Kappa Crucis and interestingly it is not the brightest star in the cluster. The distance to the cluster is some 2.0 kpc and some of the bright stars appear to be foreground objects.

Visually the cluster is very appealing. The bright B-type blue stars show a very beautiful color contrast with the bright M2 red supergiant. The colours are striking, even in small telescopes.

As always,

"Give it a go and let us know!
Good luck and great viewing!"