Jewel Box

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This article is about the constellation. For the type of ballpark, see Baseball park.

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

It was one of the finest open clusters discovered by Nicolas Louis de Lacaille when he was in South Africa during 1751–1752. 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 7,600 light years from Earth.

This famous group of young bright stars is an open cluster some 7800 light years from the Sun. It 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 is kappa Crucis, and it contrasts strongly against its predominantly blue, hot companions. Kappa Cru is a very large, (hence very luminous) quite young star in its red supergiant stage, which paradoxically indicates that its life is drawing to a close. The cluster is looks like a star to the unaided eye and appears close to the eastern-most star of the Southern Cross, so is only visible from southern latitudes.

The great variety of star colors in this open cluster underlies its name: The Jewel Box. One of the bright central stars is a red supergiant, in contrast to the many blue stars that surround it. The cluster, also known as Kappa Crucis contains just over 100 stars, and is about 10 million years old. It lies about 7500 light-years away, so the light that we see today was emitted from the cluster before even the Great Pyramids in Egypt were built. The Jewel Box spans about 20 light-years, and can be seen with binoculars towards the constellation of the Southern Cross, also known as Crux.