Open cluster in Hydra
M48
Lost for the same reason as M47 — a recording error put it five degrees from where it is. Large and bright enough to be a naked-eye smudge from a dark site, which makes the error the more remarkable. The recovery was the same kind of detective work and came in 1934.
What makes the loss remarkable is the object: fifty-four arcminutes across and bright enough to see without a telescope from a dark site, which is to say a thing you could trip over, mislaid for a hundred and fifty years by a slip of the pen.
- Catalogue
- M48
- Type
- Open cluster
- Constellation
- Hydra
- Distance
- 1,500 light-years
- Apparent magnitude
- 5.8
- Surface brightness
- 23.1 mag/□″
- Apparent size
- 54′
- Right ascension
- 8h 14m
- Declination
- −5.80°
- Found by
- Charles Messier, 1771
Magnitude 5.8 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
Large, loose and bright enough to show as a smudge to the naked eye under a dark sky. Binoculars are the right instrument; a telescope at low power will do. About eighty stars in an elongated group with a few chains running through it.
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 6°S.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 24° | |
| 51°N London, Calgary | 33° | |
| 40°N New York, Madrid | 44° | |
| 30°N Cairo, Houston | 54° | |
| 0°N the equator | 84° | |
| 33°S Sydney, Cape Town | 63° |
Nearby in the sky
The whole catalogue →Nothing else in the catalogue is especially close; the nearest is 12° apart, which is a separate trip rather than a nudge of the tube. Everything below is measured from M48 itself, not from the middle of Hydra.
- M46 Open cluster 12° apart Puppis · magnitude 6.1 · binoculars from Bortle 9 or darker
- M47 Open cluster 13° apart Puppis · magnitude 4.4 · binoculars from Bortle 9 or darker
- M50 Open cluster 18° apart Monoceros · magnitude 5.9 · binoculars from Bortle 9 or darker
- M93 Open cluster 19° apart Puppis · magnitude 6.2 · binoculars from Bortle 9 or darker
One of 110. Positions J2000; the sky is the final authority.