Nebula in Orion
Orion Nebula (M42)
Not really a cloud at all: it is a hollow cavity blown into the side of a much larger dark one, and we can see inside only because the near wall happened to break open. The four stars of the Trapezium at its heart did the blowing, and are still doing it.
It is also the nearest place where heavy stars are being made, which makes it the reference against which every other star-forming region is understood — most of what is known about how planetary systems begin was learned by pointing telescopes at the discs of dust around young stars in this one nebula.
- Catalogue
- M42
- Type
- Nebula
- Constellation
- Orion
- Distance
- 1,340 light-years
- Apparent magnitude
- 4.0
- Surface brightness
- 21.9 mag/□″
- Apparent size
- 85′ × 60′
- Right ascension
- 5h 35m
- Declination
- −5.45°
- Found by
- Nicolas-Claude Fabri de Peiresc, 1610
Magnitude 4.0 sounds comfortable and is spread over 85′, which brings it down to 21.9 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?
Straightforward from a Bortle 3 sky or darker, and aperture makes almost no difference to that — spread this thinly, an object is limited by how bright the sky behind it is rather than by how much light the telescope collects. A darker site beats a bigger telescope.
| 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/□″ | Challenge | Challenge | Challenge | Challenge | Challenge |
| Bortle 5 20.3 mag/□″ | Challenge | Challenge | Challenge | Challenge | Challenge |
| 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
The one object that exceeds its photographs in a different direction rather than falling short of them. Any instrument shows the glow; 150mm shows the wings and the dark intrusion; the four Trapezium stars split cleanly at moderate power, and a fifth and sixth appear at 200mm on a steady night.
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 M42 itself, not from the middle of Orion.
- M43 De Mairan's Nebula 11′ apart Orion · magnitude 9.0 · needs more than binoculars
- M78 Nebula 6.2° 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.