Collinder 47

Collinder 47 is a large, bright open star cluster in the constellation Perseus, also known as Cr 47, NGC 1528 and Melotte 23. Its distance in a recent photometric study gives roughly 3,100 light-years, It is a rich cluster of about 100 to 165 member stars, spanning roughly 16 to 23 arcminutes. It is a young cluster, with age estimates ranging from about 110 to 370 million years, and it has little reddening, which gives it a strong blue colour. It lies less than 1.5° northwest of the cluster NGC 1545 (Collinder 49), close to the emission nebula Sh2-209, and just under 3° north of Mu Persei. At magnitude 6.4 it is well worth a look, and William Herschel discovered it in 1790.