Globular cluster in Hydra
M68
A southern globular that never climbs far from northern latitudes and is ignored for it. Catch it near the meridian with 200mm and it begins to break into stars; catch it low and it is a smear.
It spans about a hundred and six light-years, sits well out in the halo, and counts among the most metal-poor globulars anywhere. Its stars carry roughly a fiftieth of the Sun's complement of heavy elements, which places its formation before most of the galaxy's disc existed to enrich anything.
- Catalogue
- M68
- Type
- Globular cluster
- Constellation
- Hydra
- Distance
- 33,600 light-years
- Apparent magnitude
- 7.8
- Surface brightness
- 21.8 mag/□″
- Apparent size
- 12′
- Right ascension
- 12h 39m
- Declination
- −26.75°
- Found by
- Charles Messier, 1780
Magnitude 7.8 sounds comfortable and is spread over 12′, which brings it down to 21.8 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 1 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/□″ | No | 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 | No | No | No | No |
| Bortle 8 18.1 mag/□″ | No | No | No | No | No |
| Bortle 9 17.8 mag/□″ | No | No | No | No | No |
At the eyepiece
Moderately concentrated and beginning to resolve at 200mm. Everything about observing it from northern latitudes is a compromise with the horizon — it culminates low and briefly, and the atmosphere takes back most of what aperture gives.
When, and from where
Highest in the middle of the night in March. A southern object: overhead at 27°S, and low and murky from Britain and the northern United States even at its best. North of 63°N it never rises.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 3° | Low — in the murk |
| 51°N London, Calgary | 12° | Low — in the murk |
| 40°N New York, Madrid | 23° | |
| 30°N Cairo, Houston | 33° | |
| 0°N the equator | 63° | |
| 33°S Sydney, Cape Town | 84° |
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 M68 itself, not from the middle of Hydra.
- M83 Southern Pinwheel 13° apart Hydra · magnitude 7.6 · binoculars from Bortle 5 or darker
- M104 Sombrero Galaxy 15° apart Virgo · magnitude 8.0 · binoculars from Bortle 6 or darker
- M61 Galaxy 32° apart Virgo · magnitude 9.7 · binoculars from Bortle 4 or darker
- M49 Galaxy 35° apart Virgo · magnitude 8.4 · binoculars from Bortle 5 or darker
One of 110. Positions J2000; the sky is the final authority.