NGC 6633 is a large, loose, open cluster in Ophiuchus.

NGC 6633 shines at magnitude 4.6, so it can be viewed with the unaided eye under good sky conditions at a dark-sky observing site. It subtends an apparent angle of 20 arcminutes, just a little smaller than the full moon.

At a distance of 1,000 light-years, this would correspond to a true size of 5.8 light-years in space.

It is estimated that there are 30 stars in NGC 6633, the brightest of which is magnitude 7.6.

NGC 6633 is estimated to be 660 million years old. It discovered by Philippe Loys de Chéseaux in 1745-46.

North is to the top in the above image.

NGC 6633 Catalogs: NGC 6633 Object Type: Open Cluster Magnitude: 4.6v Size: 20' Constellation: Ophiuchus Image Field Centered At: RA: 18h 27m 52s Dec: +06° 31' 10"