M 39 Deep sky · Open cluster in Cygnus · M 39 · NGC 7092
M 39
A large, loose open cluster near Deneb, too wide for most telescopes and just right for binoculars: a triangle of stars on the Milky Way.
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- Type
- Open cluster
- Designations
- M 39 · NGC 7092
- Constellation
- Cygnus
- Apparent magnitude
- 4.6
- Apparent size
- 31′
- Position (J2000)
- RA 21h 32m · Dec +48° 26′
It is about as wide as the full Moon, which is about 31′ across. The Sun comes no nearer to it than 58°, around mid March, so it is never lost in the Sun’s glare, which reaches about 15° out.
When to see it
On the night of Thu 12 Aug 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | Never sets | 01:08 · 87° | — |
| New York EDT | 13:56 | 01:03 · 82° | 12:09 |
| Singapore GMT+8 | 19:08 | 01:13 · 43° | 07:18 |
| Sydney GMT+10 | 21:23 | 00:04 · 8° | 02:46 |
Common questions
- Can I see it from 50° north?
- Yes, on any clear night of the year. From there it never sets: it is circumpolar, circling the pole and still 8° up at its lowest.
- Can I see it from 35° south?
- Only just. At its highest it is 7° above the northern horizon, so it needs a clear, flat view that way and clean air.
- When is the best time of year to see it?
- Around mid August, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by mid November it is highest in the early evening, and in mid May not until the hours before dawn.
- Naked eye, binoculars or telescope?
- The naked eye, from a dark country sky, which shows stars to about magnitude 7.0; from a city, binoculars.
Look for
From Deneb sweep north-east along the Milky Way. It is plain in binoculars, and sometimes to the naked eye from a dark site.
Look for
From 50° north it is circumpolar and never sets; from 35° north it climbs to 77°; from the equator it climbs to 42°; from 35° south it barely clears the horizon, at 7°.
Look for
Magnitude 4.6 against the faintest star each can show: the eye under a city sky, 4.5 (0.1 short); the eye under a dark country sky, 7.0 (2.4 to spare); 50 mm binoculars under that dark sky, 11.0 (6.4 to spare); a 100 mm telescope there, 12.5 (7.9 to spare). Through 7×50 binoculars, whose field is about 7.1° across, it spans 7% of the field’s width; through a 100 mm telescope at 50×, a field about 1° across, it spans 52% of the field’s width.