The open star cluster NGC 4755 in the constellation Crux (Southern Cross), is one of the most beautiful star clusters on the sky. The brightest stars in the cluster are blue super giants, which shine a 1000 times brighter than our sun. The highlight of the cluster is a single red super giant, which likely caused Sir John Herschel to call this cluster "a box of differently colored precious stones".
NGC 4755 has a distance of 7000 light years. The brightest stars are located in a spatial volume of 25 light years diameter, which is equivalent to 10 arc minutes in the sky. This star cluster is roughly 10 million years old and therefore one of the youngest open star clusters. The area on the picture is roughly equivalent to the size of the moon.