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The open cluster NGC 4755 stunned its discoverer Nicolas Louis de Lacaille when he first saw it from South Africa (1751-52). Its more than 100 stars, contained in a 12 arcmin area, are mostly blue giants, with the exception of the double DU Cru, an M2 class supergiant that strongly contrasts with its blue companions and helps to understand the name of the cluster (The Jewel Box).
Additional Info
Object
Name(s): NGC 4755, Caldwell 94, The Jewel Box Cluster
Type: Open Cluster
RA: 12h 53m 38.7s
Dec: -60º 20’ 53.2”
Constellation: Crux
Size (arcmin): 10
Magnitude: +4.2
Distance: 6,400 ly
Image
Date: 2015-06-08 thru 12
Size (arcmin): 19×19
Telescope: Planewave CDK 20” f/6.8
Camera: SBIG 16803 (4096x4096pix)
Guiding: Astrodon MonsterMOAG off-axis guider
Total exposure: 140 min (L: 36min; RGB: 104min)
Processing: CCDStack, Photoshop CC 2016 and PixInsight