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| Emission nebula | |
|---|---|
| H II region | |
|   As seen by the legacy survey | |
| Observation data: J2000 epoch | |
| Right ascension | 17h 51m 42s | 
| Declination | −28° 54′ 00″ [1] | 
| Distance | 7600 pc | 
| Apparent dimensions (V) | 10' [2] | 
| Constellation | Sagittarius | 
| Designations | RCW 142, LBN 4 | 
| See also: Lists of nebulae | |
Sh 2-21 is an emission nebula in the constellation Sagittarius. It is part of the Sharpless Catalog assembled by Stewart Sharpless. It is associated with four infrared clusters, [DB2000] 7, [DB2000] 10, [DB2000] 11 and [DB2000] 12. Open cluster Collinder 351 is included as part of the nebula complex. [3]
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