Messier 21
Star cluster in Sagittarius · 4,250 light-years
🔭 Explore Messier 21 in the 3D map →View Messier 21 images →| Type | Star cluster |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 04m 13s |
| Declination | −22° 29′ |
| Object distance | 4,250 light-years |
| Apparent magnitude | 5.9 |
| Apparent size | 6′ (arc-minutes) |
| Approx. true diameter | 7.4 light-years across |
| Also known as | M21 · NGC 6531 |
Messier 21 is a star cluster (also catalogued as NGC 6531) in Sagittarius — a gravitationally bound family of stars sharing a common origin. It was recorded by Charles Messier in his famous catalogue of 110 deep-sky objects. It spans roughly 6 arc-minutes on the sky. At about magnitude 5.9, it is an easy target for binoculars and small telescopes.
Although it appears about 6′ wide on the sky, its real span is roughly 7.4 light-years — the difference is a measure of how far away it lies.
Observing Messier 21
Messier 21 lies in the constellation Sagittarius and is best placed in the evening sky around June. Its maximum altitude above the horizon depends on your latitude. It is best placed for observers in the southern hemisphere, and sits low for those far north. It is a comfortable target for binoculars and small telescopes.
See Messier 21 in Universe Finder
Open the interactive 3D map to fly to Messier 21 and see it in context among the real stars around it. Launch the 3D view →
Sources
- Position, magnitude and angular size from the OpenNGC catalogue (Mattia Verga).
- Object identity cross-referenced with SIMBAD (CDS, Strasbourg).
- Image credits and the original observation source are linked with each photograph.
Related objects
- Pleiades — star cluster
- Hercules Cluster — star cluster
- Small Sgr Star Cloud — star cluster
- Messier 25 — star cluster
- Messier 103 — star cluster