Jewelbox Cluster: NGC 4755: CRUX

The Jewel Box (also known as NGC 4755 or Kappa Crucis Cluster) is an open cluster in the constellation of Crux. As Kappa Crucis, it has a Bayer designation despite the fact that it is a cluster rather than an individual star.

It is one of the finest open clusters discovered by Nicolas Louis de Lacaille when he was in South Africa during 17511752. This cluster is one of the youngest known, with an estimated age of only 7.1 million years. It has an apparent magnitude of 4.2, and is located 6,440 light years from Earth and contains around 100 stars.

This famous group of young bright stars was named the Jewel Box from its description by Sir John Herschel as "a casket of variously coloured precious stones," which refers to its appearance in the telescope. The bright orange star Kappa Crucis contrasts strongly against its predominantly blue, hot companions. Kappa Crucis is a very large (hence very luminous) young star in its red supergiant stage, which paradoxically indicates that its life is drawing to a close. The cluster looks like a star to the unaided eye and appears close to the easternmost star of the Southern Cross, (Beta Crucis), so is only visible from southern latitudes.

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• JBox