Open cluster in Monoceros
M50
A heart-shaped scattering of about a hundred stars with one conspicuously red one on its southern edge. Pleasant rather than remarkable, which is a fair description of most of what Messier logged in winter.
It formed about a hundred and fifty million years ago and lies in a stretch of Monoceros that has almost nothing else in it, so it holds a low-power field on its own. The red star on the edge is a giant and is probably not a member at all, merely a foreground star arranged conveniently.
- Catalogue
- M50
- Type
- Open cluster
- Constellation
- Monoceros
- Distance
- 3,200 light-years
- Apparent magnitude
- 5.9
- Surface brightness
- 20.5 mag/□″
- Apparent size
- 16′
- Right ascension
- 7h 03m
- Declination
- −8.33°
- Found by
- Giovanni Domenico Cassini, before 1711
Magnitude 5.9 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
About a hundred stars in a rough heart or arrowhead, depending on what you are inclined to see, with one obviously red star near the southern edge that is worth hunting for. Low to moderate power. A pleasant twenty minutes rather than a revelation.
When, and from where
Highest in the middle of the night in January. Close enough to the celestial equator to rise from almost anywhere on Earth, and to pass overhead for anyone near 8°S.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 22° | |
| 51°N London, Calgary | 31° | |
| 40°N New York, Madrid | 42° | |
| 30°N Cairo, Houston | 52° | |
| 0°N the equator | 82° | |
| 33°S Sydney, Cape Town | 65° |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 10° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M50 itself, not from the middle of Monoceros.
- M47 Open cluster 10° apart Puppis · magnitude 4.4 · binoculars from Bortle 9 or darker
- M46 Open cluster 11° apart Puppis · magnitude 6.1 · binoculars from Bortle 9 or darker
- M41 Open cluster 13° apart Canis Major · magnitude 4.5 · binoculars from Bortle 9 or darker
- M48 Open cluster 18° apart Hydra · magnitude 5.8 · binoculars from Bortle 9 or darker
One of 110. Positions J2000; the sky is the final authority.