M23
Open Cluster in Sagittarius
About
A large open cluster in Sagittarius, about 2,050 light-years away and roughly 330 million years old. Estimates of its membership range from about 170 to 410 stars.
Imaging tips
- Framing: roughly 900–1,500 mm on APS-C, or 1,380–2,290 mm on full frame.
- A wide field shows more than the cluster: one 180 mm frame, 3.4° × 2.2°, placed M23 low in the frame with the dark nebula Barnard 84a at the top and LDN 288 and LDN 285 just above.
- Milky Way dust surrounds the cluster: in one 23-hour stack of 5-minute frames it was so prominent that the cluster itself was almost hard to see.
- No narrowband needed: that imager found no hydrogen-alpha-rich regions in the field. Best around June and July; about 21° altitude at most from 50°N.
Facts
- Size
- 27′
- Magnitude
- 5.5
- Coordinates
- RA 17h 56.9m, Dec −19° 1′
- Framing, APS-C
- 900–1500 mm
- Framing, full frame
- 1380–2290 mm
- Best months
- Jun, Jul
- Peak altitude
- 21° from 50°N, 36° from 35°N