The Jewel Box (also known as the Kappa Crucis cluster, NGC 4755, or Caldwell 94) is an

open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Crux CRUX is a lightweight x86-64 Linux distribution targeted at experienced Linux users and delivered by a tar.gz-based package system with BSD-style initscripts. It is not based on any other Linux distribution. It also utilizes a ports system ...

, originally discovered by Nicolas Louis de Lacaille in 1751–1752. This cluster was later named the Jewel Box by

John Herschel Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor and experimental photographer who invented the blueprint and did botanical work. ...

when he described its telescopic appearance as "... a superb piece of fancy jewellery". It is easily visible to the naked eye as a hazy star some 1.0° southeast of the first-magnitude star Mimosa (Beta Crucis). This hazy star was given 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 base of the A-shaped asterism of the cluster. This cluster is one of the youngest known, with an estimated age of 14 million years. It has a total integrated

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

4.2, is located 1.99 kpc, or 6497

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s from Earth, and contains just over 100 stars.

Discovery and observation

The Jewel Box as a star cluster was first found by Nicolas Louis de Lacaille while doing astrometric observations for his 1751–1752 southern star catalogue '' Cœlum Australe Stelliferum'' at the

Cape of Good Hope The Cape of Good Hope ( ) is a rocky headland on the Atlantic Ocean, Atlantic coast of the Cape Peninsula in South Africa. A List of common misconceptions#Geography, common misconception is that the Cape of Good Hope is the southern tip of Afri ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

. He saw this as a nebulous cluster in his small 12 mm telescope, but was first to recognise it as a group of many stars. The name "Jewel Box" comes from

's own 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." Herschel recorded the positions of just over 100 members of the cluster in 1834–1838.

Prominent members

The central part of the cluster is framed by bright stars making up an A-shaped asterism. The upper tip of this asterism is HD 111904 ( HR 4887, HIP 62894), a B9 supergiant and suspected variable star. It is the brightest member of the A asterism at magnitude 5.77. The brightest star in the region of the cluster is the variable DS Cru (HD 111613, HR 4876), which lies well beyond the A asterism. It is a B9.5 α Cyg variable supergiant with an average visual brightness of magnitude 5.72, but is thought to be a foreground object. The bar of the "A" consists of a line of four stars, three of which are sometimes called the

traffic lights Traffic lights, traffic signals, or stoplights – also known as robots in South Africa, Zambia, and Namibia – are signaling devices positioned at road intersections, pedestrian crossings, and other locations in order to control the flow o ...

. On the right (south) is BU Cru, a magnitude 6.92 B2 supergiant and

eclipsing binary A binary star or binary star system is a Star system, system of two stars that are gravity, gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved ...

. Next to it is BV Cru, a magnitude 8.662 B0.5

giant In folklore, giants (from Ancient Greek: ''wiktionary:gigas, gigas'', cognate wiktionary:giga-, giga-) are beings of humanoid appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''gia ...

and Beta Cephei variable. Next in line is DU Cru, an M2

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) and a stellar classification K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelg ...

that varies irregularly between magnitude 7.1 and 7.6 . The last of the four is CC Cru, a magnitude 7.83 B2 giant and ellipsoidal variable. Each leg of the base of the asterism's outline is marked by a blue supergiant star. HD 111990 (HIP 62953) is magnitude 6.77 and B1/2 . The star κ Cru itself is magnitude 5.98 and B3.

Physical characteristics

The Jewel Box cluster is one of the youngest known

s. The mean

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

of the Jewel Box cluster is . The brightest stars in the Jewel Box cluster are

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range ...

s, and include some of the brightest stars in the

Milky Way galaxy The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galaxy, which are ...

. Calculating its distance is difficult due to the proximity of the

Coalsack Nebula The Coalsack Nebula (Southern Coalsack, or simply ''the'' Coalsack) is a dark nebula, which is visible to the naked eye as a dark patch obscuring part of the Milky Way east of Acrux (Alpha Crucis) in the constellation of Crux (constellation), Cru ...

, which obscures some of its light.

Observation

The Jewel Box cluster is regarded as one of the finest objects in the southern sky. It is visible to the naked eye as a hazy object of the fourth magnitude. It can be easily located using the star Beta Crucis as a guide, and appears as a fourth magnitude object. It is impressive when viewed with binoculars or a small or large telescope. Three members along the crossbar of the A-shaped asterism lie in a straight line known as the 'traffic lights' due to their varying colours.

Gallery

File:Wide Field Image of the Jewel Box.jpg, Wide Field Image of the Jewel Box File:Digitized Sky Survey 2 Image of NGC 4755.jpg, Digitized Sky Survey 2 image of the Jewel Box File:A Hubble gem - the Jewel Box.jpg, Hubble image of the Jewel Box File:Putting the Jewel Box in perspective (composite image).jpg, Putting the images in perspective File:NGC 4755 "El Joyero" a través de un pequeño telescopio.jpg, The Jewel Box seen through a small amateur telescope

References

External links

* * * {{DEFAULTSORT:Jewel Box (star cluster) Open clusters Crux NGC objects 094b