Open cluster
M18 (M18)
In Sagittarius (Sgr) • Magnitude 7.5 • 9.0 arcminutes
Open the free AstroPlanner with M18 pre-selected, scored against your telescope, location, and the live cloud forecast.
A sparse, young open cluster nestled between the dazzling Omega Nebula and the Sagittarius Star Cloud, easily overlooked in such rich company. Its stars are estimated to be only about 32 million years old — a cosmic newborn, formed long after the dinosaurs went extinct.
M18 at a glance
| Catalog IDs | M18, N 6613 |
| Type | Open cluster |
| Constellation | Sagittarius (Sgr) |
| Right ascension | 18h 19m 55s |
| Declination | -17° 04' 48" |
| Apparent magnitude | 7.50 |
| Angular size | 9.0 × 9.0 arcmin |
| Max altitude at 45°N | 28° |
| Best imaging months | Mar, Apr, May |
How to image M18
M18 sits in the constellation Sagittarius at right ascension 18h 19m 55s and declination -17° 04' 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.