M25
Open Cluster in Sagittarius
About
An open cluster in Sagittarius, about 2,000 light-years away and roughly 68 million years old. It contains the Cepheid variable U Sagittarii and has a dark lane near its centre.
Imaging tips
- Framing: 760–1,260 mm on APS-C or 1,160–1,930 mm on full frame.
- The dark lane splits the cluster into a northern and a southern part, so frame it with room around the centre.
- Modest data is enough: one imager used 36 minutes of luminance plus 30 minutes each of R, G and B at 1.17″ per pixel; another took three 8-minute frames at 530 mm through a light-pollution filter.
- Broadband colour suits it. Best around June and July; about 21° altitude at most from 50°N.
Facts
- Size
- 32′
- Magnitude
- 4.6
- Coordinates
- RA 18h 31.6m, Dec −19° 7′
- Framing, APS-C
- 760–1260 mm
- Framing, full frame
- 1160–1930 mm
- Best months
- Jun, Jul
- Peak altitude
- 21° from 50°N, 36° from 35°N