Open cluster
Ptolemy's Cluster (M7)
In Scorpius (Sco) • Magnitude 3.3 • 1.3 degrees
Open the free AstroPlanner with Ptolemy's Cluster pre-selected, scored against your telescope, location, and the live cloud forecast.
One of the most ancient objects in any catalogue — Greek astronomer Ptolemy noted this naked-eye cluster in 130 AD, nearly two millennia before Messier was born. At just 800 light-years away, it sprawls across an area of sky larger than three full Moons.
Ptolemy's Cluster at a glance
| Catalog IDs | M7, N 6475 |
| Type | Open cluster |
| Constellation | Scorpius (Sco) |
| Right ascension | 17h 53m 53s |
| Declination | -34° 49' 48" |
| Apparent magnitude | 3.30 |
| Angular size | 80.0 × 80.0 arcmin |
| Max altitude at 45°N | 10° |
| Best imaging months | Mar, Apr, May |
How to image Ptolemy's Cluster
Ptolemy's Cluster sits in the constellation Scorpius at right ascension 17h 53m 53s and declination -34° 49' 48". 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.