Open cluster in Auriga
M38
The faintest of the Auriga three, its brighter stars falling into a rough cross. The small cluster NGC 1907 sits just south of it at almost exactly the same distance, and whether the two are a genuine pair or simply passing each other has been argued both ways.
The cross shape survives magnification better than most asterisms do, and there is a yellow giant near the middle that gives the eye somewhere to settle. Whether NGC 1907 is a companion or a passer-by turns on velocities that are barely different enough to measure, and the current reading is that they are simply meeting.
- Catalogue
- M38
- Type
- Open cluster
- Constellation
- Auriga
- Distance
- 4,200 light-years
- Apparent magnitude
- 7.4
- Surface brightness
- 22.6 mag/□″
- Apparent size
- 21′
- Right ascension
- 5h 29m
- Declination
- +35.83°
- Found by
- Giovanni Batista Hodierna, before 1654
Magnitude 7.4 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 1 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/□″ | No | 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
The faintest of the three and the most oddly shaped — the brighter stars fall into a cross or, to some people, the Greek letter pi. Sweep half a degree south for NGC 1907, which is small, tight and much older, and makes a good contrast in the same field.
When, and from where
Highest in the middle of the night in December. Well placed for the northern hemisphere and overhead for anyone near 36°N. South of 54°S it stays below the horizon.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 66° | Never sets |
| 51°N London, Calgary | 75° | |
| 40°N New York, Madrid | 86° | |
| 30°N Cairo, Houston | 84° | |
| 0°N the equator | 54° | |
| 33°S Sydney, Cape Town | 21° |
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 M38 itself, not from the middle of Auriga.
- M36 Open cluster 2.3° apart Auriga · magnitude 6.3 · binoculars from Bortle 9 or darker
- M37 Open cluster 5.9° apart Auriga · magnitude 6.2 · binoculars from Bortle 9 or darker
- M1 Crab Nebula 14° apart Taurus · magnitude 8.4 · binoculars from Bortle 5 or darker
- M35 Open cluster 14° apart Gemini · magnitude 5.3 · binoculars from Bortle 9 or darker
One of 110. Positions J2000; the sky is the final authority.