Object Of The Week May 5, 2024 - Jewel Box

[wvreeven]

NGC 4755, Caldwell 94, Melotte 114, Kappa Crucis Cluster, Jewel Box

Open Cluster

Crux

RA: 12 53 39.6
DEC: -60 22 16

Mag: 4.2
Diam: 10.3’ x 10.3’

Sorry for the rather short article this week.

The Jewel Box cluster often is hailed as one of the most beautiful open clusters in the southern, or even the entire, sky. It was discovered by Nicolas de Lacaille in 1751 or 1752 from South Africa. The cluster already is visible to the naked eye and Lacaille saw it as a nebulous cluster in his 12 mm (yes, that’s not a typo) telescope. The famous name "Jewel Box" comes from John Herschel who compared the cluster to a fancy piece of jewellery. The same John Herschel recorded the positions of just over 100 members between 1834 and 1838.

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Credit: ESO (https://www.eso.org/public/images/eso0940a/)

The brightest stars in the cluster are between magnitudes 5.8 and 7.8 and form a characteristic asterism shaped like a letter A. All of them are B-type stars except one which lies almost exactly in the center of the A and is an M2 red supergiant named DU Crucis. Like DU Crucis, many of the B-type stars are variable, some with a very small and others with a somewhat larger amplitude. One of the bright stars is Kappa Crucis and interestingly it is not the brightest star in the cluster. The distance to the cluster is some 2.0 kpc and some of the bright stars appear to be foreground objects.

Visually the cluster is very appealing. The bright B-type blue stars show a very beautiful color contrast with the bright M2 red supergiant. The colours are striking, even in small telescopes.

As always,

"Give it a go and let us know!
Good luck and great viewing!"

[lamperti]

Back in 1998, while in Aruba for the eclipse, I was able to see this beauty in a pair of 11x80 binoculars from the hotel balcony: "Very resolvable and would be pretty in a telescope." It was one of 44 binocular objects seen over two nights that were not easily seen from home location up north.

[akarsh]

In a recent observing session from south India (13°N latitude), I was quite amazed to see the Jewel Box with the naked eye! Of course, with an 8" telescope, it was a pretty sight despite extinction from the high humidity.

[Clear Skies]

Two observations in my log (https://clearskies.eu/astronomy/observing/observinglog/) for the Jewel Box, back in 2008 (https://clearskies.eu/astronomy/observing/sessions/sessions2008/) during my first visit to Sutherland, South Africa (https://en.wikipedia.org/wiki/Sutherland,_South_Africa), in the early days... I mean nights of my astronomy 'career'.

The morning of 8 January (https://clearskies.eu/astronomy/observing/sessions/sessions2008/7jan2008/), using a 5" Mak @ 106x / 36', the colors of some of the brightest stars in the cluster were notable:


Quite detached and quite concentrated, not especially rich. In the NNW and ENE part fewer stars are visible than there are in other parts of the cluster. The color difference of the stars in the cluster is notable: there is a white-yellow star in the NNW part, just NNE of the middle is the orange-red star CD-59 04459, just WSW thereof is a yellow star, SSW of the middle is white-yellow star, to the ENE is a pale orange star, NNE of the orange-red star is another pale orange star, otherwise there are many mag. 9 and fainter stars with unresolved stars in the background.

The following night (https://clearskies.eu/astronomy/observing/sessions/sessions2008/8jan2008/) using 10x50 binos:


Through binoculars it is notable that the cluster has a triangular shape: the brightest stars form a triangle pointing just south of the star Beta Crucis (that is towards the NW). In the tip of the triangle is a yellow star, centrally in the WSW leg is an orange star, on the SSE side is a white star.



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Here's the guide (https://clearskies.eu/csog/downloads/dsfootw2024#18).

[cloudbuster]

This is one of the most famous clusters in the Southern Hemisphere, so my expectations were high when I finally saw it in its full glory during a trip to Namibia. Frankly, the first sight was a tiny bit disappointing because it turned out to be not a very rich cluster and not very large either. But a lot was made up for by the fun shape, the huge difference in brightness and of course the color of the stars to which it owes its nickname.

The brightest stars together form a kind of triangle with in the middle a line of 3 bright stars with different colors (like a traffic light). The top star is yellow, the middle one blue and the bottom one orange. This is a very nice sight through the telescope, but on my sketch the colors remain a bit faded. Furthermore, the cluster consists of much dimmer stars that squeeze together in angular bends, making the whole even look a bit "unreal". So in the end, I thought of it as quite an extraordinary cluster, this Jewel Box.


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[kisspeter]

The Jewel Box was the first object I drew on my first trip to the southern hemisphere. I already decided at home that I want to draw on our first night as well. And that my target would be NGC 4755. This drawing actually took almost two full nights. But it was totally worth it. The colors are not that vivid in the 4" Newtonian but certainly visible.

4", 40x (10mm Delos), 1.8°
2012, Hakos, Namibia
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