The Jewel Box (also known as the Kappa Crucis Cluster, NGC 4755, or Caldwell 94) is an
open cluster 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 origins of the e ...
Crux, 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, experimental photographer who invented the blueprint and did botanical wor ...
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 of 4.2, is located 1.95
kpc. or 6,440
light year
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
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 ( af, Kaap die Goeie Hoop ) ;''Kaap'' in isolation: pt, Cabo da Boa Esperança is a rocky headland on the Atlantic coast of the Cape Peninsula in South Africa.
A common misconception is that the Cape of Good Hope is t ...
in
South Africa. He saw this as a nebulous cluster in his small 12mm. (½-inch) telescope, but was first to recognise it as a group of many stars.
[http://www.docdb.net/show_object.php?id=ngc_4755, DOCdb : Jewel Box][
]
The name "Jewel Box" comes from
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, experimental photographer who invented the blueprint and did botanical wor ...
'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. On the right (south) is
BU Cru, a magnitude 6.92 B2 supergiant and
eclipsing binary. Next to it is BV Cru, a magnitude 8.662 B0.5
giant and
Beta Cephei variable. Next in line is
DU Cru, an M2
red supergiant 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
Rotating ellipsoidal variables are a class of variable star. They are close binary systems whose components are ellipsoidal. They are not eclipsing, but fluctuations in apparent magnitude occur due to changes in the amount of light emitting area ...
.
[
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 open clusters. The mean radial velocity
The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...
of the Jewel Box cluster is .
Observation
The Jewel Box cluster is regarded as one of the finest objects in the southern sky.
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
The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
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
SEDS: NGC 4755
with a Copyright Anglo-Australian Observatory Image of NGC 4755
*
A Copyright T. Warner Amateur Image of NGC4755
{{DEFAULTSORT:Jewel Box (star cluster)
Open clusters
Crux (constellation)
NGC objects
094b