NGC 6397 [SEP] constellation
NGC 6397
NGC 6397, also known as Caldwell 86, is a globular cluster in the constellation Ara. It is located about 7,800 light-years from Earth, making it one of the two nearest globular clusters to Earth (the other one being Messier 4). The cluster contains around 400,000 stars, and can be seen with the naked eye under good observing conditions.
NGC 6397 is one of the at least 20 globular clusters of the Milky Way Galaxy that have undergone a core collapse, meaning that the core
within a globular cluster were not resolved until Charles Messier observed M 4 in 1764. The first eight globular clusters discovered are shown in the table. Subsequently, Abbé Lacaille would list NGC 104, NGC 4833, M 55, M 69, and NGC 6397 in his 1751–1752 catalogue.
When William Herschel began his comprehensive survey of the sky using large telescopes in 1782 there were 34 known globular clusters. Herschel discovered another 36 himself and was the first to resolve virtually all of them into stars