M 55 Deep sky · Globular cluster in Sagittarius · M 55 · NGC 6809
Specter Cluster
A large, loose globular cluster low in the southern summer sky, found by Nicolas-Louis de Lacaille from the Cape of Good Hope.
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- Type
- Globular cluster
- Designations
- M 55 · NGC 6809
- Constellation
- Sagittarius
- Apparent magnitude
- 7.4
- Apparent size
- 19′
- Position (J2000)
- RA 19h 40m · Dec −30° 58′
The full Moon, about 31′ across, is 1.6 times as wide. The Sun passes 9° from it around mid January, and for about 23 days of the year it sits within 15° of the Sun, lost in its glare.
When to see it
On the night of Wed 14 Jul 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 22:27 | 01:11 · 8° | 03:55 |
| New York EDT | 21:11 | 01:06 · 18° | 05:01 |
| Singapore GMT+8 | 19:21 | 01:17 · 58° | 07:12 |
| Sydney GMT+10 | 16:34 | 00:08 · 87° | 07:41 |
Common questions
- Can I see it from 50° north?
- Only just. At its highest it is 9° above the southern horizon, so it needs a clear, flat view that way and clean air.
- Can I see it from 35° south?
- Yes, and well placed: at its highest it passes almost overhead, 86° up, above most of the air’s haze.
- When is the best time of year to see it?
- Around mid July, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by mid October it is highest in the early evening, and in mid April not until the hours before dawn.
- How bright is it?
- Magnitude 7.4 in total, but that light is spread over 19′ of sky: on average 22.4 magnitudes per square arcsecond. Against a dark country sky that average stands out; a city’s glow drowns all but its brightest parts.
- Naked eye, binoculars or telescope?
- Binoculars. At magnitude 7.4 it is past the eye, but a 50 mm pair under a dark sky reaches about magnitude 11.0.
Look for
It is east of the Teapot, on an empty stretch of sky. From the south it climbs high; from the north, it barely clears the horizon.
Look for
From 50° north it barely clears the horizon, at 9°; from 35° north it climbs to 24°; from the equator it climbs to 59°; from 35° south it climbs to 86°.
Look for
Magnitude 7.4 against the faintest star each can show: the eye under a city sky, 4.5 (2.9 short); the eye under a dark country sky, 7.0 (0.4 short); 50 mm binoculars under that dark sky, 11.0 (3.6 to spare); a 100 mm telescope there, 12.5 (5.1 to spare). Those limits are for a point of light; its light is spread over its whole size, so it needs some of that margin in hand. Through 7×50 binoculars, whose field is about 7.1° across, it spans 4% of the field’s width; through a 100 mm telescope at 50×, a field about 1° across, it spans 32% of the field’s width.
Words used here
Its constellation
Nearby in Sagittarius
- Nebula Lagoon Nebula
- Nebula Trifid Nebula
- Globular cluster Great Sagittarius Cluster
- Nebula Omega Nebula
- Open cluster Black Swan Cluster
- Open cluster Webb's Cross
- Open cluster M 23
- Open cluster Small Sagittarius Star Cloud
- Open cluster M 25
- Globular cluster M 28
- Globular cluster M 54
- Globular cluster M 69
- Globular cluster M 70
- Globular cluster M 75