M21
Open Cluster in Sagittarius
About
A young open cluster in Sagittarius, about 3,900 light-years away and roughly 6.6 million years old. It lies close to the Trifid Nebula on the sky but is not physically associated with it.
Imaging tips
- About 13′ across: roughly 1,860–3,110 mm on APS-C spans a third to half of the frame with the cluster alone.
- It is a cluster, so broadband colour is the choice; one imager recorded it with only two 5-minute exposures at f/10.
- It lies about 38′ from the Trifid (M20), nearby and within a wide frame; one write-up notes it often gets overlooked beside M20 and M8.
- Best around June and July; stays below about 18° altitude from 50°N.
Facts
- Size
- 13′
- Magnitude
- 5.9
- Coordinates
- RA 18h 4.1m, Dec −22° 30′
- Framing, APS-C
- 1860–3110 mm
- Framing, full frame
- 2860–4760 mm
- Best months
- Jun, Jul
- Peak altitude
- 18° from 50°N, 33° from 35°N