The Jewel Box, NGC 4755, is a young open cluster in Crux whose blue-white stars and single red supergiant reminded John Herschel of a casket of gems.
At a glance
| type | open star cluster |
|---|---|
| distance from the Sun | 6,450 light-years (1.98 kpc) |
| its light left it | 6,450 years ago |
| size in the piece | about 14 light-years acrossmodel |
Read off the piece’s own catalogue, the same values it draws with. Model marks a property of the piece’s galaxy model rather than a measurement.
About Jewel Box
NGC 4755, also called the Kappa Crucis Cluster, sits beside Beta Crucis in the Southern Cross and next to the dark Coalsack. It is visible to the eye as a fuzzy star. John Herschel described it as a casket of variously coloured precious stones, and the name stuck: through a telescope its brilliant blue-white supergiants frame a single striking orange-red one.
The cluster is young, so its most massive stars are still burning, though the brightest have already left the main sequence and swollen into supergiants. That red supergiant shows how fast a heavy star evolves: born with the others, it has already reached a stage its lighter siblings will take far longer to reach.
What you see in the piece
In the piece it is a compact swarm of stars, mostly hot and blue-white. From Earth it sits beside the Coalsack; fly out and the dark cloud, much nearer the Sun, falls away from it.
Questions
Why is it called the Jewel Box?
John Herschel compared its contrasting blue-white and orange-red stars to a casket of variously coloured precious stones.
How far away is the Jewel Box?
The Jewel Box is 6,450 light-years (1.98 kpc) from the Sun, so its light left it 6,450 years ago.