Open cluster in Cancer
M67
Four billion years old, where most open clusters come apart within a few hundred million. It survived by sitting well above the galactic plane, out of reach of everything that would normally have pulled it to pieces: a cluster that got out of the way.
It is also one of the best-studied objects in the sky for a reason that has nothing to do with looks: a cluster of that age with a known distance is a laboratory for stellar evolution, because every star in it began at the same moment from the same material and only mass has separated them since.
- Catalogue
- M67
- Type
- Open cluster
- Constellation
- Cancer
- Distance
- 2,700 light-years
- Apparent magnitude
- 6.1
- Surface brightness
- 22.1 mag/□″
- Apparent size
- 30′
- Right ascension
- 8h 50m
- Declination
- +11.82°
- Found by
- Johann Gottfried Koehler, 1779
Magnitude 6.1 for the cluster as a whole, though that is a sum rather than a thing you see: what reaches you is a scatter of separate stars, and whether you catch it depends on how bright the brightest of them are. Why surface brightness is the number that matters.
Could you see it?
Straightforward with the naked eye from Bortle 4 or darker; with 10×50 binoculars from Bortle 9.
| 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/□″ | Easy | Easy | Easy | Easy | Easy |
| Bortle 5 20.3 mag/□″ | No | Easy | Easy | Easy | Easy |
| Bortle 6 19.3 mag/□″ | No | Easy | Easy | Easy | Easy |
| Bortle 7 18.6 mag/□″ | No | Easy | Easy | Easy | Easy |
| Bortle 8 18.1 mag/□″ | No | Easy | Easy | Easy | Easy |
| Bortle 9 17.8 mag/□″ | No | Easy | Easy | Easy | Easy |
At the eyepiece
Two hundred or so stars, evenly spread, with a scattering of orange ones through them that give it a different colour from every other open cluster here. That colour is the age showing: these stars have had four billion years to get old, and most clusters never get the chance.
When, and from where
Highest in the middle of the night in February. Passes overhead at 12°N and rises from everywhere except the far south — below 78°S it never clears the horizon.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 42° | |
| 51°N London, Calgary | 51° | |
| 40°N New York, Madrid | 62° | |
| 30°N Cairo, Houston | 72° | |
| 0°N the equator | 78° | |
| 33°S Sydney, Cape Town | 45° |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 8.5° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M67 itself, not from the middle of Cancer.
- M44 Beehive Cluster 8.5° apart Cancer · magnitude 3.1 · binoculars from Bortle 9 or darker
- M48 Open cluster 20° apart Hydra · magnitude 5.8 · binoculars from Bortle 9 or darker
- M95 Galaxy 28° apart Leo · magnitude 9.7 · binoculars from Bortle 4 or darker
- M96 Galaxy 28° apart Leo · magnitude 9.2 · binoculars from Bortle 5 or darker
One of 110. Positions J2000; the sky is the final authority.