NGC 6633
Open cluster in the constellation of Ophiuchus
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NGC 6633 is a large bright open cluster in the constellation Ophiuchus. Discovered in 1745-46 by Philippe Loys de Chéseaux, it was independently rediscovered by Caroline Herschel in 1783 and included in her brother William's catalog as H VIII.72.[1] Bright enough to be seen with the naked eye, the cluster is considered a fine object for binoculars or small telescopes.[2]
| NGC 6633 | |
|---|---|
Open cluster NGC 6633 | |
| Observation data (J2000.0 epoch) | |
| Right ascension | 18h 27.7m |
| Declination | 6° 34′ |
| Distance | 1.04 kly |
| Apparent magnitude (V) | 4.6 |
| Apparent dimensions (V) | 27′ |
| Physical characteristics | |
| Estimated age | 550 million years |
| Other designations | NGC 6633, De Cheseaux No. 3 H VIII.72, Cr 380, Mel 201 |
| Associations | |
| Constellation | Ophiuchus |
NGC 6633 is also known as the Tweedledum Cluster (paired with IC 4756 as Tweedledee), also as the Captain Hook Cluster and the Wasp Cluster.[3] It is also designated Collinder 380 or Melotte 201. Nearly as large as the full moon, the cluster contains 38 known stars[4] and shines with a total magnitude of 4.6; the brightest star is of mag 7.6. Its age has been estimated at 550 million years.[5]
The cluster contains at least one chemically peculiar star - NGC 6633 48 (BD+06 3755).[4]
The 8th-magnitude binary star HD 169959 (NGC 6633 58) is within the line-of-sight of the open cluster but is not physically associated with it.[4]
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