Nebula in Orion
De Mairan's Nebula (M43)
Part of the Orion Nebula, and separate only because a lane of foreground dust makes it look separate. De Mairan catalogued the comma in 1731, Messier kept it apart, and every list since has quietly inherited the mistake.
The dust lane responsible is part of the same cloud that shapes the whole complex, and the comma is lit by a single star of about seven solar masses. Nothing about the division is physical, which is a useful reminder about the rest of the catalogue: Messier was cataloguing appearances, and appearances are what a foreground can rearrange.
- Catalogue
- M43
- Type
- Nebula
- Constellation
- Orion
- Distance
- 1,340 light-years
- Apparent magnitude
- 9.0
- Surface brightness
- 23.8 mag/□″
- Apparent size
- 20′ × 15′
- Right ascension
- 5h 36m
- Declination
- −5.27°
- Found by
- Jean-Jacques Dortous de Mairan, 1731
Magnitude 9.0 sounds comfortable and is spread over 20′, which brings it down to 23.8 per square arcsecond — the number that actually decides whether there is anything to see. Why surface brightness is the number that matters.
Could you see it?
Nothing in the common range of amateur equipment makes this straightforward under any sky — it is a photographic target, or one for patience and a very large aperture.
| Sky | Eye | 10×50 | 80mm | 130mm | 200mm |
|---|---|---|---|---|---|
| Bortle 1 21.9 mag/□″ | No | Challenge | Challenge | Challenge | Challenge |
| Bortle 2 21.7 mag/□″ | No | No | No | No | No |
| Bortle 3 21.4 mag/□″ | No | No | No | No | No |
| Bortle 4 20.9 mag/□″ | No | No | No | No | No |
| Bortle 5 20.3 mag/□″ | No | No | No | No | No |
| Bortle 6 19.3 mag/□″ | No | No | No | No | No |
| Bortle 7 18.6 mag/□″ | No | No | No | No | No |
| Bortle 8 18.1 mag/□″ | No | No | No | No | No |
| Bortle 9 17.8 mag/□″ | No | No | No | No | No |
At the eyepiece
Separated from M42 by a dark lane that is obvious once pointed out and invisible until then. It is a comma of light around a single star, and the trick is deliberately looking at it as a thing in its own right rather than letting the eye slide back to the main nebula.
When, and from where
Highest in the middle of the night in December. Close enough to the celestial equator to rise from almost anywhere on Earth, and to pass overhead for anyone near 5°S.
| Latitude | Highest it gets | |
|---|---|---|
| 60°N Oslo, Anchorage | 25° | |
| 51°N London, Calgary | 34° | |
| 40°N New York, Madrid | 45° | |
| 30°N Cairo, Houston | 55° | |
| 0°N the equator | 85° | |
| 33°S Sydney, Cape Town | 62° |
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 M43 itself, not from the middle of Orion.
- M42 Orion Nebula 11′ apart Orion · magnitude 4.0 · binoculars from Bortle 3 or darker
- M78 Nebula 6.0° apart Orion · magnitude 8.3 · binoculars from Bortle 4 or darker
- M79 Globular cluster 19° apart Lepus · magnitude 7.7 · binoculars from Bortle 5 or darker
- M50 Open cluster 22° apart Monoceros · magnitude 5.9 · binoculars from Bortle 9 or darker
One of 110. Positions J2000; the sky is the final authority.