Open cluster in Gemini
M35
Large and rich, and with a bonus: the small, much more distant cluster NGC 2158 sits at its edge, five times further away and ten times older. Seeing both in one field is seeing two different eras of the galaxy at once.
NGC 2158 is the older of the two by roughly a factor of ten, and it looks it: yellow where M35 is blue, and compact where M35 is scattered. Seeing them together is the clearest demonstration in the sky of what happens to an open cluster given time — and the answer is that it goes red, tightens, and eventually stops existing.
- Catalogue
- M35
- Type
- Open cluster
- Constellation
- Gemini
- Distance
- 2,800 light-years
- Apparent magnitude
- 5.3
- Surface brightness
- 21.2 mag/□″
- Apparent size
- 28′
- Right ascension
- 6h 09m
- Declination
- +24.33°
- Found by
- Philippe Loys de Chéseaux, 1745
Magnitude 5.3 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 5 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/□″ | Easy | 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
Among the best sights in the winter sky, and better still for its neighbour. M35 fills a low-power field with bright stars; NGC 2158 sits at the south-west edge as a small dense knot that will not resolve. Having both at once is the whole reason to come here.
When, and from where
Highest in the middle of the night in December. Passes overhead at 24°N and rises from everywhere except the far south — below 66°S it never clears the horizon.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 54° | |
| 51°N London, Calgary | 63° | |
| 40°N New York, Madrid | 74° | |
| 30°N Cairo, Houston | 84° | |
| 0°N the equator | 66° | |
| 33°S Sydney, Cape Town | 33° |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 8.2° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M35 itself, not from the middle of Gemini.
- M1 Crab Nebula 8.2° apart Taurus · magnitude 8.4 · binoculars from Bortle 5 or darker
- M37 Open cluster 9.0° apart Auriga · magnitude 6.2 · binoculars from Bortle 9 or darker
- M36 Open cluster 12° apart Auriga · magnitude 6.3 · binoculars from Bortle 9 or darker
- M38 Open cluster 14° apart Auriga · magnitude 7.4 · binoculars from Bortle 9 or darker
One of 110. Positions J2000; the sky is the final authority.