NGC 4755 The Jewel Box

Being part of the Southern Cross, the jewel box can’t be missed when searching the area. This remarkable and beautiful open cluster is located at just about 1 arc degree southeast from Mimosa (β Cru).

I had seen this object through the binoculars various times, but this time I had the mission to spot it with the telescope and then perform a sketch of it.

The sky was clear; the constellation was ±25° above the horizon. The full moon was setting. Even in those good conditions, the only stars visible with the naked eye in this region of the sky were α Cen and β Cen and the four forming the Southern Cross (mostly stars of 1^st and 2^nd magnitude).

In the 20mm erecting eyepiece, it appears as a bright group of stars forming a triangle which reminds me of the Hyades shape. 

The image with the 10mm eyepiece is much more extraordinary:  the six stars forming the triangle stand out, appearing like a group of precious stones, just like Sir John Herschel described them in the XIX century, deserving the name he gave them. Beside the right side of the triangle’s base (in the image at 9-10 hours from the inverted triangle’s center), there is a very fine group of stars, unresolved with the binoculars that make the region seem to glow with a haze surrounded by some stars above 10 magnitude.

The jewel box was first catalogued as a star with the Greek letter K (kappa) in the Bayer’s catalogue and was posteriorly discovered as an apparently nebulous object consisting of many stars by Nicolas Louis de Lacaille during 1751-1752. About 80 years later, it was named by Sir John Hershel as the Jewel Box and even though

the whole cluster is also known as the Kappa Crucis cluster, its second brightest star (left side of the inverted triangle’s base in the sketch) received the nomenclature of K Cru.  Forming a triangle with K Cru stars, there are HIP62918 supergiant red star and HIP62913, which is a double star (HIP HIP62913 A and HIP62913 B). I saw this double star, forming a obtuse triangle with HIP62918.

Enjoy this marvelous creation of God!

Blessings,

LG



Edited by Jennifer Steinberg (editor in chief)

SOURCES

http://www.astrostudio.org/

http://en.wikipedia.org/