The Jewel Box Cluster

It is only fitting that on the (9th) anniversary of SSRO's first attempt to image from PROMPT/CTIO on June 30, 2006, we finally replace our original Jewel Box Cluster with an updated version! 

This cluster was one of the finest open clusters discovered by Abbe Lacaille when he was in South Africa during 1751-1752. 

The Jewel Box is one of the youngest known, with an estimated age of only 7.1 million years.  Its hottest star is of spectral type B0. According to Burnham, the 3 brightest stars are blue giants of mag 5.75 and spectral type B9, mag 5.94 and type B3, and mag 6.80/B2, while the fourth brightest star is a mag 7.58 M2 red supergiant. Another mag 5.7/spectral type A1 star is probably also a member, another white supergiant:  This star would be the brightest of the cluster at about absolute magnitude -7.7 (83,000 solar luminosities).

Situated close to the cluster is a huge dark area of the sky, right within the band of the Milky Way called the "Coal Sack".  This is a huge dark nebula, probably the nearest at 500 to 600 light years distance, and 60 to 70 light years diameter.