M21 (NGC 6531)
Also known as M21 · M 21 · NGC 6531
M21 (NGC 6531) is an open star cluster in the constellation Sagittarius, about 3,930 light-years from Earth.
Facts
| Type | Open star cluster |
|---|---|
| Constellation | Sagittarius |
| Position (J2000) | 18h 04m 13s, −22° 29′ |
| Distance | 3,930 light-years (its light set off about 3,930 years ago) |
| Brightness | magnitude 5.9 (smaller is brighter; the faintest stars the eye sees are about 6) |
| Size on the sky | 110′ × 110′ (the full Moon is about 31′) |
| Filter | No filter (It shines in starlight of every colour, so a nebula filter would only dim it; a dark sky helps more.) |
| Studied in | 158 scientific papers (SIMBAD) |
When and how to see it
M21 (NGC 6531) is highest in the sky at midnight in June. From India (about 20° N) it climbs to about 48° above the horizon; from 50° N, to about 18°. To see it you need the naked eye from a dark site.
Heights are worked out for India and for 50° N. Set your location in Settings to see them for where you are.
For tonight's best time from your own town, the darkness and the Moon, open it on the map and see its "Tonight from your location" card.
More in Sagittarius
- Lagoon Nebula (M8)
- M18 (NGC 6613)
- M23 (NGC 6494)
- Omega Nebula (M17)
- Sagittarius A*
- Sagittarius Cluster (M22)
- Sagittarius Star Cloud (M24)
- Trifid Nebula (M20)
Everything in Sagittarius · All 88 constellations · All sky objects
Data: SIMBAD (CDS, Strasbourg; the site's weekly copy) · OpenNGC · Data sources & credits