Deepsky observing
Finding the Jewel Box
Posted 2007 January 12 @ 10:23 - filed under Astronomy.
Just off the tip of the short arm of Crux, the Southern Cross, lies the famous open star cluster nicknamed the Jewel Box.
This small but bright star grouping is easy to find in binoculars, a short distance from the bright star beta Crucis. It lies at the northern edge of the Coalsack, a large dark nebula that fills a binocular field of view. For a printable star chart, click on the thumbnail diagram above.
The Jewel Box can be seen with the naked eye if the skies are dark enough, so it's impossible to say who the first person was to see it. The first telescopic observation was made by the Jesuit astronomer Abbe de Lacaille, who visited Cape Town in 1752. In the 1820s it was recorded by James Dunlop, who observed it from Paramatta in New South Wales, Ausralia.
Jewel Box factsheet
Names: Jewel Box, NGC 4755, Collinder 264, Melotte 114, Raab 96, ESO 131-SC016, OCL 892, Lund 627
RA: 12h 53m 42s, Dec: -60° 22.0'
Constellation: Crux
Magnitude: 4.2 V
Size: 5 arcmin
Age: ±16 million years
Distance: ±6,600 light years
The cluster was made famous by Sir John Herschel, who observed it often during his stay in Cape Town in the mid-1830s. "A most vivid and beautiful cluster", he wrote, "... though neither large nor a rich one, is yet an extremely brilliant and beautiful object when viewed through an instrument of sufficient aperture to show distinctly the very different colour of its constituent stars, which give it the effect of a superb piece of fancy jewellery."
In astronomical parlance, the cluster is known as NGC 4755, which means it is the 4,755th object in the New General Catalogue, an authoritative catalogue of known objects in our Milky Way and beyond, compiled in the late 19th century. Today, many more objects have been catalogued and examined – within our Milky Way galaxy, hundreds of thousands of star clusters and nebulae have been recorded. Beyond the Milky Way, 9,500,000 objects are known, the vast majority of which are galaxies, each with many millions of stars, clusters and nebulae of their own!
The Jewel Box is included in the "Top 100 Deepsky Objects", an observing project by the Deepsky Observing Section of the ASSA. If you have binoculars or a telescope, why not have a go at these gems of the southern skies?
- RELATED LINKS
- RECENT PUBLICATIONS
Two recent research reports discuss the complex issue of dating the Jewel Box, and determining its distance. They can be downloaded as PDFs from the arXiv website:
The VLT-FLAMES Survey of Massive Stars (2006 Jun)
On the difference between nuclear and contraction ages (2006 Mar)
Keywords: Astronomy, deepsky observing, NGC 4755, Kappa Crucis cluster, Jewel Box, Herschel's Jewel Box
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