NGC 6633 is an open cluster in Ophiuchus. WEBDA puts its distance at 1226 light years. They put its age at 426 million years while SEDS says 660 million years. This is one of the Herschel 400 objects which I'm imaging when nothing else is in position. This cluster is almost too big for my 33'x 22' field of view. It was discovered by Philippe Loys De Chéseaux in 1745 (maybe 1746). Caroline Herschel later made an independent rediscovery on July 31, 1783. While it is in the original H400 program he was the third to find it on July 30, 1788. My entry from May 20, 1985 on a good night at 65x with my 10" f/5 reads, "Large, scattered cluster of very bright stars most of which can be seen in binoculars. In fact, it is best seen in my 10x50 binoculars. Seems larger than the 20' usually stated for it."

This is in a very rich star field but a very sparse cluster. I had to greatly restrain the background stars limiting how deep this image goes. Otherwise, the cluster was lost in the Milky Way. The cluster contains only about 30 stars.

14" LX200R, L=3x10' RGB=2x10', STL-11000XM, Paramount ME