Right ascension 18 27.7 Distance 1.04 kly Apparent dimensions (V) 27′ | Declination 6° 34′ Apparent magnitude (V) 4.6 Estimated age 660 million years | |
 | ||
NGC 6633 is an open cluster, in the constellation Ophiuchus, that was, according to the Webb Society Deep-Sky Observer's Handbook, Volume 3 (Open and Globular Star Clusters), p. 3, discovered in 1745-46 by Philippe Loys de Chéseaux. It was independently rediscovered by Caroline Herschel, and been included in her brother's catalog as H VIII.72.
This cluster is nearly as large as the full moon, and contains 30 stars which make it shine at a total magnitude of 4.6; the brightest star is of mag 7.6. Its age was estimated at 660 million years.
References
NGC 6633 Wikipedia(Text) CC BY-SA