Open cluster in Puppis
M47
A lost Messier: he wrote the position down with a sign error and nothing was there, so it stayed missing until 1959, when somebody worked out the arithmetic mistake. Bright, loose, and a degree and a half from M46.
The error was Messier's arithmetic rather than his eyes: he had the offsets right and the signs wrong, and the correction in 1959 put the object back within a few arcminutes of where it belonged. It is around seventy-eight million years old and its brightest members are blue giants, one of which is a fine double.
- Catalogue
- M47
- Type
- Open cluster
- Constellation
- Puppis
- Distance
- 1,600 light-years
- Apparent magnitude
- 4.4
- Surface brightness
- 20.4 mag/□″
- Apparent size
- 30′
- Right ascension
- 7h 37m
- Declination
- −14.50°
- Found by
- Giovanni Batista Hodierna, before 1654
Magnitude 4.4 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 7 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/□″ | Easy | Easy | Easy | Easy | Easy |
| Bortle 7 18.6 mag/□″ | Easy | 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
The opposite of M46 in every respect, and close enough to visit in the same sweep: coarse, bright, easily resolved, forty-odd stars including several doubles. Take them one after the other and the difference between a young scattered cluster and an old rich one explains itself.
When, and from where
Highest in the middle of the night in January. Overhead at 14°S and southerly enough to sit low from northern Europe, though never out of reach there — only north of 76°N does it stop rising at all.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 16° | Low — in the murk |
| 51°N London, Calgary | 25° | |
| 40°N New York, Madrid | 36° | |
| 30°N Cairo, Houston | 46° | |
| 0°N the equator | 76° | |
| 33°S Sydney, Cape Town | 72° |
Nearby in the sky
The whole catalogue →One more of the catalogue sits within five degrees, close enough to take in on the same night without moving far. Everything below is measured from M47 itself, not from the middle of Puppis.
- M46 Open cluster 1.3° apart Puppis · magnitude 6.1 · binoculars from Bortle 9 or darker
- M93 Open cluster 9.6° apart Puppis · magnitude 6.2 · binoculars from Bortle 9 or darker
- M50 Open cluster 10° apart Monoceros · magnitude 5.9 · binoculars from Bortle 9 or darker
- M48 Open cluster 13° apart Hydra · magnitude 5.8 · binoculars from Bortle 9 or darker
One of 110. Positions J2000; the sky is the final authority.