Globular cluster in Aquarius
M2
Maraldi found it on 11 September 1746 while chasing a comet, and Messier found it again, independently, on 11 September 1760 — the same date, fourteen years apart. It stays a fuzzy ball until about 150mm, when the edges begin to grain.
It is one of the larger globulars in the catalogue, about 175 light-years across and something like thirteen billion years old, and it sits in a notably empty stretch of Aquarius with nothing bright nearby to guide you in. Star-hopping to it is most of the work.
- Catalogue
- M2
- Type
- Globular cluster
- Constellation
- Aquarius
- Distance
- 33,000 light-years
- Apparent magnitude
- 6.5
- Surface brightness
- 21.1 mag/□″
- Apparent size
- 16′
- Right ascension
- 21h 34m
- Declination
- −0.82°
- Found by
- Jean-Dominique Maraldi, 1746
Magnitude 6.5 sounds comfortable and is spread over 16′, which brings it down to 21.1 per square arcsecond — the number that actually decides whether there is anything to see. Why surface brightness is the number that matters.
Could you see it?
Straightforward with the naked eye from Bortle 3 or darker; with 10×50 binoculars from Bortle 5.
| Sky | Eye | 10×50 | 80mm | 130mm | 200mm |
|---|---|---|---|---|---|
| Bortle 1 21.9 mag/□″ | Easy | Easy | Easy | Easy | Easy |
| Bortle 2 21.7 mag/□″ | Easy | Easy | Easy | Easy | Easy |
| Bortle 3 21.4 mag/□″ | Easy | Easy | Easy | Easy | Easy |
| Bortle 4 20.9 mag/□″ | No | Easy | Easy | Easy | Easy |
| Bortle 5 20.3 mag/□″ | No | Easy | Easy | Easy | Easy |
| Bortle 6 19.3 mag/□″ | No | Challenge | Challenge | Challenge | Challenge |
| Bortle 7 18.6 mag/□″ | No | Challenge | Challenge | Challenge | Challenge |
| Bortle 8 18.1 mag/□″ | No | No | No | No | No |
| Bortle 9 17.8 mag/□″ | No | No | No | No | No |
At the eyepiece
A tight ball that stubbornly refuses to break up. At 100mm it is a fuzzy star with a bright middle; at 200mm the outer edges start to crumble into points, and the sense of depth arrives all at once when they do. Higher magnification helps here more than it does with looser clusters.
When, and from where
Highest in the middle of the night in August. Close enough to the celestial equator to rise from almost anywhere on Earth, and to pass overhead for anyone near 1°S.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 29° | |
| 51°N London, Calgary | 38° | |
| 40°N New York, Madrid | 49° | |
| 30°N Cairo, Houston | 59° | |
| 0°N the equator | 89° | |
| 33°S Sydney, Cape Town | 58° |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 13° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M2 itself, not from the middle of Aquarius.
- M15 Globular cluster 13° apart Pegasus · magnitude 6.2 · binoculars from Bortle 5 or darker
- M73 Asterism 15° apart Aquarius · magnitude 9.0 · binoculars from Bortle 6 or darker
- M72 Globular cluster 15° apart Aquarius · magnitude 9.4 · binoculars from Bortle 4 or darker
- M30 Globular cluster 22° apart Capricornus · magnitude 7.2 · binoculars from Bortle 5 or darker
One of 110. Positions J2000; the sky is the final authority.