PART ONE : A. 1752 — 1834

Naked-eye observations of NGC 4755 were not made in the ancient literature or southern cultures. Although easily visible by Ptolemy in the 2nd Century AD, no earlier reference has found. Perhaps this is not surprising, as unlike large open clusters like the Pleiades (M45) or Praesepe — The Beehive, or some of the bright southern clusters; the Southern Pleiades (IC 2602), NGC 2516 in far-southern Carina, or even M6 or M7 close to the tail of Scorpius; the Jewel Box is fairly small.

This well-known southern cluster was first described as the hazy star Kappa by Bayer in his Uranometria of 1603 AD. Later in 1752, Abbe Lacaillé listed it in his second listing of Nebulous Stars and Clusters and list the object as Lac-II-12 (12h 39.2m. −59°01′; January 1752) by stating ;

5 or 6 small stars between two of sixth magnitude.

It was James Dunlop who made one of the first detailed drawing and observation of NGC 4755. He listing the cluster as Δ301 in his 629 object catalogue of 1827, stating he saw;

(Chi Crucis, Bode) [Herschels Brackets] is five stars of the 7th magnitude, forming a triangular figure, and a star of 9th magnitude between the second and third, with a multitude of very small stars on the south side.

Dunlop's Drawing 1828

In this paper is a drawn figure of Δ301 that Dunlop has, for some reason made very oddly distorted. Some of the stars do differ very slightly from how it appears today — even though Dunlop emphatically says; Figure 13, is a very correct representation. Also just as oddly is the missing central star of the bar, which is probably one of the most obvious features. It is also suprising that he hasnt drawn Kappa Crucis itself as being the brighter star, while the bright blue star at the apex of the cluster seems too faint against the brightness of the other stars. These differences lead some to conclude that the clusters appearance had undergone significant changes ( See History of the Jewel Box Part C. 1860-1872. ), which is highly unlikely considering the slow proper motions of stars within open clusters and what we now know about the nature of stellar evolution over short timescales.

Also within this text is an interesting remark that, according to Dunlop, the star is marked as Chi (χ) and not the Bayer/ Bode designation Kappa (κ). Furthermore, this nomenclature continued until the beginning of the 20th Century, as several paper published by Francis Abbott, George Ellery and H.C. Russell, for example, still used the Greek letter χ or Chi.

Of course, at least in regards the unorganised state of the ancient or medieval constellations, Crux was at one time or another was assigned as an integral part of Centaurus. From about one thousand years ago, many of the bright stars of both Crux and Pointers became invisible in much of Europe by the slow effects of precession, and these stellar assignments were generally forgotten. This state of affairs continued into about the mid-17th Century, until at least, when several European explorers being travelling into the Antipodes.

Although the usage of Chi was slowly discontinued, its use had not be properly extinguished even well after James Dunlops time. Today the modern 4.5 magnitude star Chi Centauri (14h 06.0m -41°11′) is placed some 19°N of β Centauri, which is nearer to the north-western corner of Lupus. John Dunlop here seems clearly wrong, making the same repeated simple error that persisted for some time. Though in all probability it can be more attributed to perhaps an older star atlas the Dunlop and the others had been using. It does seem that the southern observer H.C. Russell in the 19th Century might have become the first to correct it. In the literature search for this whole article, he was likely the first to refer to the cluster as Kappa Crucis in 1870. At present the lowest ranked Greek letter currently in use within Crux μ Crucis, which is also a wide pair suitable for binoculars.

B. 1834 — 1899

Sir John Herschel was the next person to view this cluster, and is giving his catalogue number HJ 3435 (or h.3435). There is little doubt that he was very impressed with what he saw — mainly from the copious amounts of written text on NGC 4755. During his four-year stay in South Africa, and using his 50cm (18-inch) f/13 reflector, all observations were made from residence Feldhausen”, which is near the Cape of Good Hope township of Claremont. He says of the Jewel Box;

The central star (extremely red) and a most vivid and beautiful cluster of from 50 to 100 stars. Among the larger there are one or two evidently greenish [stars.]; south of the red star is one 13th magnitude [Argenlander magnitudes], also red; and near its one 12th magnitude, bluish… The same red star taken. Several others laid down, of different shades of green.

This similar quote has also been duplicated in several sources. I.e. Rev. Thomas W. Webbs Celestial Objects for Common Telescopes Vol. 2, p.278 (1917).

Herschel found the cluster very conspicuous, noting with clear admiration the great extent of the colours. Oddly, he described many of the component stars as greenish. This is immediately quite strange for an astronomical description, as green is both hard to see and rare — even among some of the bright and prominent colour-contrasting double stars. I can only conclude that Herschel is describing his overall impression of the stars rather than the individual stars actually being greenish. It is quite possible that Herschel is describing what he sees. Sometimes I wonder what may cause this is more likely the speculum mirrors, which under certain circumstances may differently absorb some wavelengths in reflecting the light — especially when the mirror was last polished to improve the mirrors reflectivity.

Like James Dunlop, John Herschel also made very detailed sketches of the cluster showing some one-hundred and ten stars. Here he says;

Though set down by Lacaillé as nebulous, and on that authority entered as a nebula in Bodes Catalogue, no nebula is perceptible in any part of the extent of this cluster, which though neither a large or rich one, is yet an extremely brilliant and beautiful object when viewed through an instrument of sufficient aperture to show distinctly very different colours of its constituent stars, which give it the effect of a superb piece of fancy jewellery. The area occupied by it is about 1/48th part of a square degree, within which area have laid down, partly from micrometric measures [from the brighter stars] and partly from inter triangulation by the eye [for the fainter stars] the stars....;

According to Auke Slotegraafs Deepsky Observers Companion, an article was published by Donald McIntyre in the Journal of the Astronomical Society of South Africa An Astronomical Bi-Centenary. Abbe de Lacaillés when visiting South Africa; 1751 / 1753”; says ;

Lacaillé includes Kappa Crucis in his Catalogue. Sir John Herschel during his residence at the Cape made repeated observations of his famous cluster, but could not see any trace of nebulosity. Yet curiously, Edward James Stone, Her Majestys Astronomer at the Cape from 1870-1879, records of one of the stars in the cluster; Nebula: a red star within it observed. (Cape Catalogue of 12,441 stars for Epoch 1880, p.316.) This red star appears to have altered brightness since John Herschel observed it, and has been speculated to have done so by others like Victorian amateur astronomer Francis Abbott in 1862. The whole cluster would have appeared nebulous to Lacaille through his tiny [12mm] … magnifying 8×. Stone, after compiling his own catalogue, wrote; if is impossible, for me at least, to the advantages which I have derived from his [Lacaillés] work.”

Richard Allen, in Star Names : Their Lore and Meaning (1899) says:

Around the 6th magnitude is the celebrated cluster of coloured stars .... the central and principal one being a deep red, …others green, blue and of various shades.

Nonetheless the colourful nature has not really impressed everyone. An example is another quotation from Allen who quotes (p.191) from the English astronomy author Miss Agnes M. Clerke (taken from System of the Stars (1881) and The Herschels and Modern Astronomy (1895) who almost bitterly states;

It must be confessed that, with moderate aperture, it fails to realise the effect of colour implied by Sir John Herschels comparison to a gorgeous piece of fancy jewellery. A few reddish stars catch the eye at once; but the blues, greens and yellows belonging to their companions are pale tints, more than half drowned in white light.

Allen correctly immediately puts down this comment by saying with some abeyance; Gould, however, called it exquisitely beautiful.

Still the clusters given name has persisted till today, and it is possibly has become one of the most famous quotes about any southern deep-sky object. I counted some thirty-five sources with the same, or oddly, slightly varied wordage. The Jewel Box name still conjures up much to the clusters mystic, and in turn, produces much interest about the southern skies.

The next recorded observations were made by Francis Abbott in 1861 from his observatory in Victoria entitled On the Cluster χ Crucis, R.A. 12h 43m 36s, N.P.D. 149° 25′ 31″ (3435, H.) Lac. 1110 (Neb.)”; MNRAS, 23, p.32-33 Aug. (1862). He nicely says;

This delightful cluster, which is estimated by Sir J. Herschel to be composed of from 50 to 100 stars,” most of which partake of well-marked and varied colours, forms an object that is scarcely perceptible to the naked eye, but when under proper optical influence it is one of the most brilliant and interesting objects in the Southern sky. …This cluster is not only an object of interest from the extreme beauty of colour and arrangement…

In most of this period the information on the cluster remained similar and generally written for popularity among visual observers. This probably concluded by the time of Dreyer in 1888, who published the deep-sky New General Catalogue — scientifically classifimg the Jewel Box among the other clusters as cl, vl, stvb, kappacrucis — Cluster, very large, stars very bright, surrounding Kappa Crucis.


Last Update : 22nd April 2016

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