Open cluster
M39 (M39)
In Cygnus (Cyg) • Magnitude 4.6 • 32 arcminutes
Open the free AstroPlanner with M39 pre-selected, scored against your telescope, location, and the live cloud forecast.
One of the nearest open clusters at just 800 light-years, making it appear large and scattered across a region four times the width of the full Moon. Its roughly 30 stars are about 278 million years old and slowly drifting apart — the cluster is already in the early stages of dispersal.
M39 at a glance
| Catalog IDs | M39, N 7092 |
| Type | Open cluster |
| Constellation | Cygnus (Cyg) |
| Right ascension | 21h 31m 48s |
| Declination | +48° 25' 48" |
| Apparent magnitude | 4.60 |
| Angular size | 32.0 × 32.0 arcmin |
| Max altitude at 45°N | 87° |
| Best imaging months | May, Jun, Jul |
How to image M39
M39 sits in the constellation Cygnus at right ascension 21h 31m 48s and declination +48° 25' 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.