NGC 6397
NGC 6397 is a globular cluster in the constellation altar. NGC 6397 has a diameter of 25.7 arc minutes and an apparent brightness of 5.7 mag.
NGC 6397 is the second closest globular cluster M4, and after only a little farther than this. In contrast to M4 but it is not obscured by an interstellar cloud, so that the individual stars that are easiest to be observed in NGC 6397. It is therefore very often used together with M4 for scientific investigations. In one of these studies, it was found by chance among the stars of NGC 6397 a about 1 billion light years distant elliptical galaxy, which is in turn surrounded by a swarm of about 200 globular clusters. It is the most distant known aggregation of globular clusters.
Neckline with single stars. The width of the image corresponds to about 1.5 minutes of arc, which corresponds to about 4 light-years.