Open cluster in Cassiopeia
M52
Bright on paper and awkward in practice, because it sits in a stretch of Milky Way so crowded that it barely separates from its own background. The Bubble Nebula lies half a degree off and is harder again.
It sits behind a fair amount of dust, which costs it about a magnitude, and it is roughly thirty-five million years old. The frustration is entirely contextual: in an emptier part of the sky this would be a fine cluster, and in Cassiopeia it competes with a background that is itself made of stars.
- Catalogue
- M52
- Type
- Open cluster
- Constellation
- Cassiopeia
- Distance
- 5,000 light-years
- Apparent magnitude
- 6.9
- Surface brightness
- 21.1 mag/□″
- Apparent size
- 13′
- Right ascension
- 23h 24m
- Declination
- +61.58°
- Found by
- Charles Messier, 1774
Magnitude 6.9 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 2 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/□″ | 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 | 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
Sixty or so faint stars in a fan, with one brighter orange one on the edge that is not a member. It takes a moment to convince yourself you have found the cluster at all rather than a random thickening of the Milky Way, which is the honest difficulty with it.
When, and from where
Highest in the middle of the night in September. Circumpolar from most of Europe, Canada and the northern United States — it never sets there at all. From south of 28°S it never rises.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 88° | Never sets |
| 51°N London, Calgary | 79° | Never sets |
| 40°N New York, Madrid | 68° | Never sets |
| 30°N Cairo, Houston | 58° | Never sets |
| 0°N the equator | 28° | |
| 33°S Sydney, Cape Town | — | Never rises |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 15° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M52 itself, not from the middle of Cassiopeia.
- M103 Open cluster 15° apart Cassiopeia · magnitude 7.4 · binoculars from Bortle 9 or darker
- M39 Open cluster 20° apart Cygnus · magnitude 4.6 · binoculars from Bortle 9 or darker
- M76 Little Dumbbell 21° apart Perseus · magnitude 10.1 · binoculars from Bortle 4 or darker
- M110 Galaxy 23° apart Andromeda · magnitude 8.5 · binoculars from Bortle 3 or darker
One of 110. Positions J2000; the sky is the final authority.