Open cluster
M23 (M23)
In Sagittarius (Sgr) • Magnitude 6.9 • 27 arcminutes
Open the free AstroPlanner with M23 pre-selected, scored against your telescope, location, and the live cloud forecast.
A rich open cluster of about 150 stars spread across an area slightly wider than the full Moon. At roughly 300 million years old, it has held together long enough for its most massive members to have already evolved into bloated giant stars.
M23 at a glance
| Catalog IDs | M23, N 6494 |
| Type | Open cluster |
| Constellation | Sagittarius (Sgr) |
| Right ascension | 17h 56m 49s |
| Declination | -19° 00' 36" |
| Apparent magnitude | 6.90 |
| Angular size | 27.0 × 27.0 arcmin |
| Max altitude at 45°N | 26° |
| Best imaging months | Mar, Apr, May |
How to image M23
M23 sits in the constellation Sagittarius at right ascension 17h 56m 49s and declination -19° 00' 36". To frame and integrate it well, AstroPlanner will compute the optimal moonless window for tonight from your location, the field-of-view fit against your sensor and focal length, the suggested total integration time given your aperture and sky Bortle class, and a cloud-aware schedule that drops it from the plan if your nearest cloud forecast spike overlaps the best altitude window.