History

Swiss astronomer Philippe Loys de Chéseaux discovered this open cluster in the years 1745-46 using a small refractor. His discoveries were presented 1746 to the French Academy of Science, but seemed to be forgotten. In 1759 Le Gentil mentioned them in a private, but it wasn't until 1892 that Guillaume Bigourdan made them public. ^[196]

Using her 4.2-inch comet-sweeper Caroline Herschel rediscovered the cluster on 31 July 1783, along with IC 4665. She entered it as #8 in her discovery log and noted: «About halfway from S Serpentarii [72 Oph] towards Theta Serpentis, a cluster of large stars. I counted about 80. Messier has it not.» On 30 July 1788 William Herschel logged this cluster as VIII 72 and noted: «A coarsely scattered cluster of large stars. C. H. 1783» As Dreyer was not aware of de Chéseaux he credited Caroline Herschel with the discovery of NGC 6633. ^{[313, 364, 464]}