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RA: 12h 53m 42s
Dec: −60° 22′ 0″
Ch: MSA:988, U2:429, SA:25
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 13r
Mag: B=?, V=4.2
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This cluster was discovered by Lacaille and included in his 1755 catalogue as Class II No. 12. In his half-an-inch 8x telescope he saw it as "five to six stars between two mag. 6 stars."
James Dunlop observed it from Paramatta, New South Wales, and included it as No. 301 in his catalogue of 1827. Using a 9-inch f/12 telescope, he described it as "five stars of the 7th magnitude, forming a triangular figure, and a star of the 9th magnitude between the second and third, with a multitude of very small stars on the south side."
Open cluster made famous by Sir John Herschel who compared it to a "superb piece of fancy jewellery." He observed it during his stay at the Cape of Good Hope with an 18inch f/13 speculum telescope. He recorded it as "the central star (extremely red) or a most vivid and beautiful cluster of from 50 to 100 stars. Among the larger there are one or two evidently greenish; south of the red star is one 13th mag, also red; and near it is one 12th mag, bluish." His next observation recorded it as "The same red star taken. Several others laid down, of different shades of green." In preparation for his meticulous sketch of the cluster, he drew up a catalogue of 110 stars, accompanied by the following explanation: "Though set down by Lacaille as nebulous, and on that authority entered as a nebula in Bode's Catalogue, no nebula is perceptible in any part of the extent of this cluster, which though neither a 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. The area occupied by it is about one-forty-eighth part of a square degree, within which area I have laid down, partly from micrometric measures (as regards the large stars) and partly from intertriangulation by the eye (as respects the small ones) the stars (110 in number)...." As regards colour, Herschel listed eight stars in which the "colour is conspicuous"; these colours are greenish-white (3 stars), green (2 stars), blue green, ruddy and red. Concerning the appearance of nebulosity mentioned above, Donald McIntyre (FRAS) in a publication of the Astronomical Society of South Africa ("An Astronomical Bi-Centenary. The Abbe de Lacaille's Visit to the Cape, 17511753") wrote: "Lacaille includes Kappa Crucis in his Catalogue. Sir John Herschel during his residence at the Cape made repeated observations of this famous cluster. but could see no trace of any nebulosity. Yet curiously, Edward James Stone, Her Majesty's Astronomer at the Cape from 1870-1879, records of one of the stars in the cluster: 'Nebula: a red start within it observed.' (Cape Catalogue of 12,441 stars for the Epoch 1880, p316). This red star appears to have altered in brightness since Sir John Herschel observed it. The whole cluster would have appeared nebulous to Lacaille through his tiny telescope of half-an-inch aperture, magnifying only 8 times. Stone, after compiling his own catalogue, wrote: 'It is impossible, for me at least, to overestimate the advantages which I have derived from his (Lacaille's) work.' "
Russell, H. C. (1872) On the coloured cluster of stars about [kappa] Crucis. MNRAS, 33(2), 66. [1872MNRAS..33...66R]
(includes a coloured chart of the cluster with positions accurately shown, and a catalogue showing magnitudes and positions)
"The following Catalogue of Stars, and the map have been made for the purpose of ascertaining whether, as asserted, any remarkable change has taken place in the relative positions and colours of the stars since they were laid down by Sir J. Herschel at the Cape ... The instrument uised is a refractor, by Merz, 7.25-inches clear aperture, 10 feet 4 inches focus, with powers from 80 to 400. The colours were examined with a 'Browning-With' reflector, of 8.5 inches, and found the same as given with the refractor. Observations were begun on 25 March 1872 but the majority of the measures were made on the night of 26h of March, which was a fine, clear night with a black sky and the stars very steady; the stars then measured were all that were visible of the cluster in full moonlight. . . . Many of the stars have drifted considerably since the Cape drawing was made, and of the stars included in that drawing, there are five small ones that I could not see; but the most remarkable fact is, that using a 7.25 in. refractor I have detected tewnty-five stars not recorded, and therefore, I think there can be no doubt, not seen by Sir John Herschel with his large reflector; and if in a small space like this twenty-five new stars may appear in so short a time, it is evidnet that more attention should be bestowed on clusters. The colours in this cluster are very beautiful and fully justify Herschel's remark that it looks like a 'superb piece of fancy jewellery.'"
Russell mentions the following colours: Yellow, with tinge of green; red; blue; between blue and green; green, with yellow tinge.
Raab, S. (1922) A research on open clusters. Lund Medd. Astron. Obs. Ser. II, 28, 1.
Discussed, based of F-A plates.
Journal BAA, 36(3), Dec, p91
remarkable colouirsl no doubt partly the result of contrast effects; contians about 130 stars in space of 1/48th square degree.
"Cat. of Open Cl. south of -45° Decl.", Mem. 17 Mnt Stromlo Obs.
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 12' and the class as 1 3 r.
Rambling through May skies: The Crux connection. Sky&Telescope, May, 439.
Mentions red SAO star in cluster.
See Thackeray A D (1949) "The Kappa Crucis Cluster" MNASSA Vol 8 p30. 10.15.2
"! cluster, fairly condensed, kappa Crucis"
Bailey, S.I. (1908) A catalogue of bright stars and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.
The RNGC (Sulentic and Tifft 1973) notes that this is a 5.0 mag open cluster.
Photo Index by Jim Lucyk: Burnhams V2 p732, Ast.Obj.for South.Tel. (Hartung, 1984), Universe Guide to Stars & Planets (Ridpath & Tirion) p258.
Hartung writes: "On a clear dark night this beautiful cluster has a jewel-like quality; it is rich and bright, about 10' across with very marked geometrical pattern and the stars show delicate colours accented by the orange red Kappa Cru. It is a good object for small apertures, and magnificent in large ones."
Simon Tsang notes that "the cluster is easy in binoculars, but was better resolved in my 6-inch at 60x. I saw a single, bright red star set among 7 or 8 yellow-white and blue-white stars, which made a very colourful contrast! At higher powers two dozen fainter stars were visible."
Harrington calls it a "dazzling 4th magnitude treasure chest of sparkling suns outside the northern edge of the Coalsack. Its brightest star, Kappa Crucis, looks like a brilliant orange-red ruby surrounded by colourful stellar gems sprinkled in the shape of an arrowhead. While it encompasses only 10 arc minutes, the unparalleled radiance of NGC 4755 more than makes up for its tiny size."
Gerd Bahr-Vollrath (Noosa Heads, Queensland, Australia) writes in The Webb Society Nebulae and Clusters Section Report No. 11, January 1993: "The famous Jewel Box cluster. About 1 degree SE of Beta Crucis, this open cluster is easily visible to the naked-eye as a diffuse star, bordering the northern rim of the Coal Sack dark nebula. Three stars of about 6th mag mark a prominent triangle about 10' across. Within and around this triangle are about 50 stars of a wide range of magnitudes, some forming apparent chains and loops. The compact size, the abundance of bright members and the fact that a deeo red star of about 7th mag lies right in the heart of the cluster rightfully earns it the name Jewel Box. A southern showpiece. (8-inch f/12 SCT)"
Arp, others: br triangle *s V=5.8,5.9,6.8. br red * V=7.42/2.19 (var by ~0.2 mag).
15cm - fine br and well condensed cl w/three br *s in triangle overlying N side of cl. 12' diam, poss a few more distant outliers, but border circ and pretty well def. 195x: 140x *s w/mod concen to center, which lies a little W of br * in center of cl, which seems cream-yel. a few close pairs, but these are mostly vf. BS, 22Feb1990, LCO.
ASSA DSOS: Ed Finlay, observing with a Meade 4-inch ED APO refractor from Johannesburg, 1992 May 22, calls it "bright but insignificant at 35x & 54x but really spectacular at 102x and 184x."
8-inch Meade, 18mm Super-Wide Angle eyepiece, 36' fov.
What a impressive beautiful bright large open cluster. Resembles mixed magnitude clear bright white and yellow to orange sparkling crystals. Smaller pinpoint stars together with some orange ones flows out to the south. About 10 arc second in size.
Date observed: 29/05/2004
Location: Boyden Observatory, Bloemfontein
Limiting Magnitude: 5
Transparency: Clean & Clear
Light Pollution: 60% moon
Weather conditions: Clear skies, slight cold wind
Instrument: 13-inch refractor, 40mm eyepiece, 15' fov
General impression of object: A stunning colourful open cluster, populated with moderate amount of stars of different brightness. Great to draw (and to start drawing experience on).
General impression of its surrounding area: Situated in rich part of milky way, easy to find due to nearby beta Crux (eye/binocular). The cluster filled almost the entire field of view of the instrument.
Description of object:
[Telescope]: NGC4755 (Jewel Box cluster) appeared as a small, faint star in the sky when looking with the naked eye. Through the telescope, multiple stars appeared of great variety - different colours, sizes and brightness. Three distinct smaller stars in a small row to the centre catch immediate attention and have greatest colour contrast in the cluster. The brightest stars envelope the little row in a virtual "bell" shape or "A". The cluster is reasonably compact. A few faint stars appear to lengthen the cluster to the east-south-east.
[Binocular]: (12x50) - Easily found, about 4-5 stars just visible making up the cluster. Appears as an "A" or "bell" shape through the binoculars. Good object to focus binocular on!
Remarks: (How good or bad the observation was and reasons)
Moonlight did not materially interfer with observation, and seems to almost have enhanced the contrast of the stars. The object was in a favourable sky position to observe and draw. Some aspects of the above description was added after the observation due to time constraints during observation.
2007 May 27, 2007 August 12
Walmer, Port Elizabeth
2.5-inch f/7.6 refractor (EP: 25mm 28x 45arcmin fov)
Conditions: Weather conditions fairly stable, partly cloudy (cc).
Herschel's Jewel Box. Very clear and easy to identify considering small size 10arcminutes; 45arcmin southeast from Mimosa (beta Crucis) M1. NGC 4755 has an apparent magnitude M 4.2 and cannot be seen with the naked eye. Prominent stars fairly equal in brightness M8.2-M8.9, belt of three stars running NE to SW M9-M10 centre of belt red star of M8.9, number of visible stars is six. Few field stars near but NGC 4755 remains rather solitary. West 15arcmin M7.8, SW 25arcmin M7.9. Cluster is not well concentrated with dark starless patches being rather prominent.
Date and Time: 12 September 2008. 20:20
Location: Prince Albert (Western Cape, South Africa).
Instrument: Orion XT10 10" f/4.7 Dobsonian Reflector
Eyepieces: 10mm (120x, 26′ FOV), 25mm (48x, 1° FOV)
Sky Conditions: Clear with bright moonlight. Seeing: 6/10. Transparency : 6/10
The Jewel Box (NGC 4755) is very easy to locate to the SE of Mimosa in Crux. The cluster as a whole is bright and easily visible in the finder scope (5° FOV).
It is a small open cluster with irregular shape containing stars of varying brightness (mag 5.7 for brightest to mag 10 for fainter stars. Stars are well resolved.
At 120x, 9 bright stars can be easily seen. With the 3 brightest forming a triangular shape pointing to the west. A very prominent orange coloured star is visible close to the centre of the triangular shape at the end of a row containing 2 other stars. These 3 stars form a row facing NE to SW. Lots of fainter stars are visible in the surrounding area.
Approximately 40 stars can be easily counted. Size of the cluster appears to be around 10 arcminutes.
Sky Conditions: Poor: Cloudy
Quality of Observation: Moderate
6" Dobsonian, 25mm & 10mm Eyepieces
The Jewel Box does its name proud, as it truly is a jewel box of stars. With bright hot stars and cooler stars, this cluster really makes for great observation. The colours of the stars in this beautiful cluster are clearly noticeable. Ranging from very bright blue to deep yellow/orange. These stars stand out so clearly on the cloudiness of the other stars in the cluster that it is truly amazing to see this cluster come to live.
Date: 2007 02 13, 21:30
Instrument: 8-inch Dobsonian, 25mm eyepiece
Sky: Clear; light pollution.
Notes: Open cluster in Crux. Small group of different coloured stars, looks just like its name – a jewel box. Three bright stars form a triangle. Halving the triangle are four stars – one bright orange, two almost greenish in colour. Surrounded by fainter stars.
This bright cluster, sitting on the northern edge of the Coalsack, is visible to the naked eye. In hand-held 8x40 binoculars, it shows as a triangular grouping with 6 stars easily visible, while a 2-inch refractor will easily show 11 prominent members. Unfortunately, no colours could be seen.
In the 15.5-inch at 220x it is an absolutely fantastic sight; three of the brighter cluster members (brilliant white in colour) form a pointed isoceles triangle, and a further three bright stars lie in a line bisecting the triangle parallel with its base. The central star of these three is red and it is flanked by a yellow-white and orange star.
A 10-inch f/5 at 120x shows this cluster very well; the three brightest stars form a pointed triangle pointing north-west. In the centre is a bright very red star with a bluish star next to it. The southernmost star of the triangle lies within a rich region of many slightly fainter (10th mag) stars. It is a very rich grouping, small, compact, with the brighter stars clearly coloured.
1997-09-20, Sutherland (Karoo), SAAO plateau. 11x80 tripod-mounted binoculars. Skies excellent. Spectacular triangle of stars with a bright knot or row of stars in the centre. The 4° binocular field around it is amazingly versatile, containing a detailed, delicate dark nebula (Coalsack), a blazing white star (Beta Cru) and a contrasting soft open cluster (NGC 4852).
Instrument:12"Dobsonian Reflector Telescope.
Sky Conditions:Dark moon and stars magnitude 6 and fainter are barely visible with the naked eye.
Transparency of the Sky:The most clear sky possible.
Seeing:Excellent clean sky,limited star flickering and brilliant objects.
First Impression:Open Cluster.
Chart Number:No.17(Extract taken out of "Atlas of the Night Sky").
Size:26mm Eyepiece:Field of View:57'/8=7.1'.
20mm Eyepiece:Field of View:50'/7=7.1'.
Size in Arc Minutes:7.1'.
Brightness Profile:High Surface Brightness.
Challenge Rating:A very stunning sight to observe in a medium to large size aperture telescope.
This open cluster presents an irregular appearance of bright stars under a black velvet sky.This cluster is well detached into bright individual stars well composed of over 25 stars arranged in the shape of a letter A with a bright orange,blue and white star.Most of the stars in this cluster is nearly the same brightness as each other although on the outskirts of this cluster there are slightly fainter stars.The stars in this cluster has contrasting appearance of sparkling stars like bright jewels in the night sky.The stars in NGC 4755 are slightly concentrated towards each other.Towards the central outskirts of this cluster there are slightly starless patches.There are also some chains of bright stars.I have found no glow of unresolved nebulosity.
The Messier objects
The Bennett objects
The Caldwell list
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