Globular cluster in Ophiuchus
M12
A cluster that has been robbed. Repeated passes through the disc of the galaxy have stripped perhaps a million stars off its outside, and what is left is the part that managed to hold on.
The theft is measurable rather than inferred: count the stars by mass and the light ones are missing, because those are the first to be pulled off when the cluster crosses the disc. What survives is a cluster made disproportionately of its own heaviest members, which is the opposite of how it started.
- Catalogue
- M12
- Type
- Globular cluster
- Constellation
- Ophiuchus
- Distance
- 15,700 light-years
- Apparent magnitude
- 6.7
- Surface brightness
- 21.3 mag/□″
- Apparent size
- 16′
- Right ascension
- 16h 47m
- Declination
- −1.95°
- Found by
- Charles Messier, 1764
Magnitude 6.7 sounds comfortable and is spread over 16′, which brings it down to 21.3 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 2 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/□″ | No | 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
The looser twin of M10, and the difference is obvious the moment you have both in one evening. It resolves more readily and looks emptier at the centre — which, given what has been taken off it, is exactly what you would expect.
When, and from where
Highest in the middle of the night in June. Close enough to the celestial equator to rise from almost anywhere on Earth, and to pass overhead for anyone near 2°S.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 28° | |
| 51°N London, Calgary | 37° | |
| 40°N New York, Madrid | 48° | |
| 30°N Cairo, Houston | 58° | |
| 0°N the equator | 88° | |
| 33°S Sydney, Cape Town | 59° |
Nearby in the sky
The whole catalogue →One more of the catalogue sits within five degrees, close enough to take in on the same night without moving far. Everything below is measured from M12 itself, not from the middle of Ophiuchus.
- M10 Globular cluster 3.3° apart Ophiuchus · magnitude 6.6 · binoculars from Bortle 5 or darker
- M107 Globular cluster 12° apart Ophiuchus · magnitude 8.1 · binoculars from Bortle 5 or darker
- M14 Globular cluster 13° apart Ophiuchus · magnitude 7.6 · binoculars from Bortle 5 or darker
- M9 Globular cluster 18° apart Ophiuchus · magnitude 7.7 · binoculars from Bortle 5 or darker
One of 110. Positions J2000; the sky is the final authority.