Jewel Box (star cluster)

Jewel Box (star cluster)

Jewel Box
NGC 4755 taken by the VLT
Credit: ESO
Observation data (J2000 epoch)
Constellation Crux
Right ascension 12h 53m 42s[1]
Declination −60° 22.0′[1]
Distance 6.4 kly[2] (1.968 kpc[3])
Physical characteristics
Mass M
Radius -
Estimated age 16Myr[3]
Notable features -
Other designations

NGC 4755,[1] Herschel's Jewel Box,[1]

Kappa Crucis Cluster,[1] Caldwell 94[4]

The Jewel Box, Kappa Crucis Cluster, NGC 4755, is an open cluster in the constellation Crux, originally discovered by Nicolas Louis de Lacaille during 1751–1752. This famous cluster was later named the Jewel Box by Sir John Herschel when he described its telescopic appearance as "a casket of variously coloured precious stones." It is easily visible to the naked eye as a hazy star some 1.0° southeast of the first-magnitude star Beta Crucis. This hazy star (the core of the cluster) was assigned the Bayer star designation Kappa Crucis, from which the cluster takes one of its common names. The modern designation Kappa Crucis has been assigned to one of the stars in the central A-shaped asterism of the cluster, the third brightest cluster star (HD 111973, HIP 62931, HR 4890), located at the base of the right leg of the A. This is a blue supergiant of spectral type B3Iae, shining at the apparent visual magnitude of 5.94. Two other cluster stars are brighter than κ Cru, namely, 5.77 magnitude star HD 111904 (HIP 62894), at the tip of the A, and HD 111613 (HIP 62732) at 5.75, which is 15 arc minutes beyond the asterism toward Beta Crucis.[5]

This cluster is one of the youngest known, with an estimated age of 14 million years. It has a total integrated magnitude of 4.2, is located 6,440 light years from Earth, and contains around 100 stars.


  • Discovery and observation 1
  • Physical characteristics 2
  • Observation 3
  • Gallery 4
  • References 5
  • External links 6

Discovery and observation

The Jewel Box as a star cluster was first determined by Nicolas Louis de Lacaille while he was doing his South African astrometric observations for his star catalogue. He saw the object as a nebulous cluster due to the small aperture of his telescope, but was the first to recognize it as consisting of many stars.[6][7] The name "Jewel Box" comes from John Herschel's description of it: "...this cluster, 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"[6]

Herschel recorded the positions of 100 members of the cluster in 1834–1838.[8]

Physical characteristics

The Jewel Box cluster is one of the youngest known open clusters. The mean radial velocity of the Jewel Box cluster is −21 kilometres per second (−13 mi/s).[3] The brightest stars in the Jewel Box cluster are supergiants, and include some of the brightest stars in the Milky Way galaxy.[9]

Calculating its distance is difficult due to the proximity of the Coalsack Nebula, which obscures some of its light.[10]


The Jewel Box cluster is regarded as one of the finest objects in the southern sky.[11] It is visible to the naked eye as a hazy object of the fourth magnitude.[12] It can be easily located using the star Beta Crucis as a guide, and appears as a fourth magnitude object.[13] It is impressive when viewed with binoculars or a small or large telescopes. The three brightest members of the cluster lie in a straight line known as the 'traffic lights' due to their varying colours.[14]



  1. ^ a b c d e "SIMBAD Astronomical Database". Results for NGC 4755. Retrieved 2006-12-14. 
  2. ^ "WEBDA Open cluster". Results for NGC 4755. Retrieved 2007-01-12. 
  3. ^ a b c Kaltcheva, N.; Golev, V.; Moran, K. (2013). "Massive Stellar Content of the Galactic Supershell GSH 305+01-24".  
  4. ^ "Deepsky Observer Companion Database". Results for NGC 4755. Retrieved 2013-06-08. 
  5. ^ NGC 4755 : The Jewel Box "The Jewel of the South" : Introduction
  6. ^ a b DOCdb : Jewel Box
  7. ^ History of the Jewel Box Part One : 1752-1834
  8. ^ Thackeray, A. D. (1949). "The Kappa Crucis Cluster". Monthly Notes of the Astronomical Society of South Africa 8: 30.  
  9. ^ Burnham, Robert (1978). Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System. New York: Dover Publications. p. 730.  
  10. ^ Consolmagno, Guy; Davis, Dan (2005). Turn left at Orion: a hundred night sky objects to see in a small telescope. Cambridge, United Kingdom: University of Cambridge. p. 189.  
  11. ^ Kaler, James B. (1989). Stars and their spectra: an introduction to the spectral sequence. University of Cambridge. p. 13.  
  12. ^  
  13. ^ Mobberley, Martin (2009). The Caldwell Objects. Springer. p. 196.  
  14. ^ Inglis, Mike (2004). Astronomy of the Milky Way: The observer's guide to the southern Milky Way. Springer. pp. 78–79.  

External links

  • SEDS: NGC 4755, with a Copyright Anglo-Australian Observatory Image of NGC 4755
  • The Jewel Box on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
  • A Copyright T. Warner Amateur Image of NGC4755