Open clusters - NGC objects 4755, 265, 290 & 6231
Why Open Clusters are Important
Stars in an open cluster make excellent laboratories in the study of the evolution of stars. Born at the same time and from the same stellar gas cloud, they all move in the same direction. Although they may have different masses, they have the same "star DNA".
Southern Sky Jewels
NGC 4755 is located at R.A.: 12:53.6 and Dec: -60:20
This cluster was discovered by Nicolas Louis de Lacaille from an observing station in South Africa during his stay there from 1751 to 1752. Herschel called NGC 4755 "the jewel box" and described it as "a casket of variously coloured precious stones". Kappa Crucis is a large and luminous aging supergiant orange star easily distinguishable against its sapphire-coloured companions. The three brightest blue stars are of magnitude 5.7 and are easy to locate.
This is an open cluster estimated to be between 7 and 10 million years old. This jewel box appears to be "falling" into the Coal Sack in the constellation Crux. Visible from southern latitudes and located east of the Southern Cross, it contains over 100 stars. It is also known as Caldwell 94 and the Kappa Crucis Cluster. There are at least 50 bright stars in this cluster located within a 10 arcminute diameter. The five brightest stars range in magnitude from 5.7 to 8.3 with the brightest star in the center of the cluster identified as a red supergiant comparable to Betelgeuse.
A Pair of Bright Sparkling Magellanic Gemstones
NGC 265 is located at R.A.: 0:47.3 and Dec: -73.29
NGC 290 is located at R.A.: 0:51.3 and Dec: -73:09
This pair of open clusters was born of the same intersteller gas cloud and are loosely held together by gravity. They are both bright (12 magnitude) compact open clusters located in the Small Magellanic Cloud spanning a distance of 65 light-years across and located 200,000 light-years in distance from the Blue Planet in the Constellation Tucana. Both open clusters consist of mainly young, hot white stars along with red supergiants, some day to meet their explosive death as supernovae.
Northern Latitude Jewel Box
NGC 6231 is located at R.A.: 16:54.0 and Dec.: -41.48
This cluster is located in the southern part of Scorpius, half a degree north of Zeta Scorpii. NGC 6231 was discovered by Giovanni Battista Hodierna, a Sicilian Roman Catholic priest, born in 1597, who taught mathematics and astronomy. It is a relatively young cluster, considered to be only about 3.2 million years old.
Although it is listed as a northern latitude target, it may be difficult to see due to its location in Scorpius. It is bright enough to be seen without visual aids under good seeing conditions. Visually, NGC 6231 is similar to the Pleiades (M45) with a central bright white giant and supergiant stars ranging in magnitude from -7 to -3.5 and glimmering as sparkling diamonds against a dark velveteen sky, some as spectroscopic binaries. If the Bull's Pleiades and the Scorpion's open cluster (NGC 6231) were in the same part of the sky, the Scorpion's cluster would be brighter.
Author: Lydia Lousteaux