Wrap up warm (if you’re in the northern hemisphere) and get all your eyepieces ready, because in this article we’ll be exploring the Great Nebula in Orion, arguably the most famous deep-sky object of them all.
M42 and M43 Vital Statistics
|Name||The Great Nebula||De Mairan’s Nebula|
|Type of Object||Emission Nebula||Emission Nebula|
|RA (2000.0)||05h 35m 24s||05h 35m 36s|
|Dec (2000.0)||-05° 27’ 00”||-05° 16’ 00”|
|Apparent Size||85 x 60 arcminutes||20 x 15 arcminutes|
|Distance||1,350 light-years||1,800 light-years|
When Was M42 Discovered and What Do We Know About it?
Despite its obvious fuzziness to the naked eye, astronomers and scholars of the pre-telescopic era paid scant attention to M42, other than assigning it the stellar classification of Theta (Θ) Orionis.
That all changed after the invention of the telescope, with the French astronomer Peiresc making the first recorded observation of the nebula in 1611, followed by the Jesuit astronomer Johann Baptist Cysatus who published an independent discovery in 1619.
Hodierna was the first to sketch the nebula in 1654, followed by Christiaan Huygens (after whom the brightest part of the nebula is named) and Le Gentil. Huygens also resolved the four stars at the heart of the nebula: the famous Trapezium (formally designated as Theta1 Orionis).
In 1733 the smaller, fainter M43 was discovered by de Mairan. Both nebulae were observed by Charles Messier in 1769 and subsequently added (along with the Beehive Cluster and the Pleiades) to the first edition of his famous catalog – apparently to ensure that his total exceeded the 42 objects in Lacaille’s 1755 list.
Whatever Messier’s motivation for including such well-known (and un-cometlike) objects, he clearly had a scientific interest in M42, observing it multiple times in 1771 and publishing a very accurate (for the time) drawing of the Great Nebula in the appendix of his catalog.
Perhaps the most prescient description of M42 came in 1789 when William Herschel called it: “an unformed fiery mist, the chaotic material of future Suns.”
A century later, American astronomer Henry Draper made a 51-minute exposure of M42: the very first photographic image of a nebula. In 1883 English astronomer Andrew Ainslie Common captured an even better image, ushering in a new era of astronomy.
Today, we recognize the Orion Nebula as the nearest star-forming region to our own sun. It’s actually not that big as star-forming regions go (certainly compared to something like M8, the Lagoon Nebula, which is approximately three times larger).
Although initially cataloged as separate objects, contemporary images clearly show that M42 and M43 belong to the same nebula, partially obscured by a band of dark dust. M42 and M43 are themselves part of a giant molecular cloud that spans much of Orion (and includes the reflection nebula M78).
The Orion Nebula owes its appearance to ionizing ultraviolet light emitted by the hot young stars in the Trapezium. This intense radiation (most of it generated by Theta1 Orionis C) is also scouring away the surrounding nebula, allowing us to see into the cavity.
Eventually, the nebula will fade to reveal a magnificent open cluster; an infrared image obtained by the ESO Very Large Telescope (VLT) shows another thousand new stars waiting to emerge from the surrounding dust and gas.
A high-resolution survey of M42 conducted with the Hubble Space Telescope has revealed well over a hundred proplyds (proto-planetary discs) within the Orion Nebula. These embryonic solar systems are in a race against time to complete their formation before they are eroded away by the fierce radiation from their faster-growing, more massive siblings.
The Hubble survey has also been used to identify dozens of brown dwarfs in M42, low-mass stars whose core temperatures are not high enough to sustain nuclear fusion.
When is M42 Visible?
This table shows when you can best see M42 from the mid-latitudes of the northern hemisphere. Times given are approximate local times for mid-month using a 24hr clock. Underlined times are during the hours of darkness.
|January||16:30||22:30||04:00||Best before midnight|
|February||14:30||20:30||02:00||Best before midnight|
|November||20:30||02:30||08:00||Best after midnight|
|December||18:30||00:30||06:00||Visible most of the night|
M42 and M43 are best seen during the winter months from November through to February.
The Orion Nebula is one of the brightest emission nebulae in the night sky, second only to the far-southern object NGC 3372, the Eta Carinae Nebula.
At a declination of -5 degrees, M42 is well-placed for observers in both hemispheres.
It’s visible to the naked eye as a fuzzy spot even from light-polluted locations, though how much of that fuzziness is due to actual nebulosity and how much is due to unresolved starlight is a matter of some contention.
I’m inclined to believe the latter explanation, although my earliest notes for M42 do describe it as having a “reddish tinge” to the naked eye. Is that observation reliable or the product of an impressionable young mind’s eye showing me what I wanted to see?
I certainly can’t see any trace of color now, but that might be caused by other factors such as aging eyesight and worsening light pollution.
How to Find M42
Popular atlas references:
- Sky & Telescope’s Pocket Sky Atlas: chart 16 (and close-up chart B)
- Sky Atlas 2000: chart 11 (and detailed chart B2)
If you face south on a clear winter’s evening, the constellation of Orion, the Hunter will likely be the first thing you notice, even from an urban location.
Our first star map shows the constellation of Orion at 9pm in the middle of February. Note the line of three bright stars across its middle, known as Orion’s belt.
Look for the fuzzy patch within the ‘sword’ which is directly south of the central star of Orion’s Belt, Alnilam. A pair of binoculars or a finderscope will show the nebulosity quite clearly, although you’ll need a telescope to resolve the stars in the Trapezium.
M42/43 through a Telescope
M42 is a majestic sight in all scopes, large and small, but don’t expect to see the full extent of the nebula – or indeed the vivid colors – familiar from images. As with most deep-sky objects, the Orion Nebula rewards careful and prolonged examination.
In my 4-inch refractor at 42x, M42 is nicely framed with layers of nebulosity building up to the core. One feature you don’t often see clearly in photographs is the Trapezium, but a small telescope will easily show all four stars, as well as the dark feature protruding into the Huygenian region. This is Sinus Magnus – popularly known as the Fish’s Mouth. A line of three bright stars (Theta2 Orionis) lies south of this area.
A narrowband filter helps the dark lanes stand out and the nebula takes on a more “threatening” appearance, like a swooping bird of prey.
In larger telescopes, M42 resembles a vast scallop shell illuminated from within by four brilliant little pearls.
At 50x in my 10-inch reflector, the green-hued Huygenian region is so bright it almost overwhelms the Trapezium. Two long “wings” curve out from the core, one sweeping south towards the 3rd magnitude multiple system Iota Orionis.
A narrowband filter significantly increases the extent of the nebula, particularly on the northern side. An OIII filter provides a similar view, but with even more contrast between the nebula and the surrounding sky. The OIII also imparts a strong green color, more so than any other object I’ve used it on.
Increasing the magnification to 92x reveals exquisite detail in and around the Huygenian region. At this power I can see a little arc of nebulosity in the cavity wall west of the Trapezium, corresponding with the sculpted section seen in images.
Medium to high magnifications are ideal for picking out fine structure in the core of the nebula – if you don’t mind losing some of the majesty of the wider, lower-power views. At 133x I can see intricate detail with both direct and averted vision, including nebulosity within the Fish’s Mouth. As well as filling out the northern half of the nebula, the narrowband filter also makes the Huygenian region seem boxier and sharper-edged.
Don’t forget to pay your respects to M43 while it’s in the field of view. In my 10-inch scope, it appears as a comma-shaped haze surrounding the 7th magnitude star NU (not Nu) Orionis. Averted vision reveals a dark lane cutting into the nebulosity.
A lacework of bright and dark structure remains visible even at a high magnification of 240x. The Trapezium stars seem to reside in a dark “hollow” within the Huygenian region, but I suspect this might be an illusory effect caused by my eye constantly re-adjusting to the brightness of the stars.
M42 is bright enough that experienced observers with large scopes have reported seeing subtle rose-pinks and other colors within the nebula. In my 10-inch scope (at 92x and 133x) I can see a distinct contrast between the southern wing and the adjacent part of the nebula, but to my eye, it’s more akin to a difference in texture than in color, like a silk ribbon next to smoke.
The Trapezium Cluster
In addition to stars A to D, another two stars in the Trapezium (above) are within reach of amateur telescopes. The visibility of the 11th magnitude E and F stars depends very much on the seeing.
I’ve seen the E star in my 4-inch refractor at 200x and it’s also visible in my 10-inch reflector at 92x without too much difficulty. The F star is more challenging due to its proximity to the brilliant Theta1 Orionis C, but on a good steady night, I can see it in the larger scope at magnifications of 133x and above.
Whether you’ve looked at the Orion Nebula once or a hundred times, there’s always something new to see in this spectacular object. I look forward to catching up with it again this winter, and I hope you do too.
Also, if you have children, why not point out M42 to them in the sky (preferably without showing them a picture first!) and ask them to describe what they see. Do they mention any mistiness, or in particular – any color?
We’d love to hear your findings in the comments.
Links / Other Info
- Star-Trapping in Orion’s Trapezium – Bob King | Sky & Telescope
- How to See the Orion Nebula in 3D – Bob King | Sky & Telescope
- The Jewel in the Sword – Howard Banich | Sky & Telescope Magazine, December 2017
- Sketches of M42 (as seen through a 28-inch telescope!) can be found on Howard’s website
- M42, M43 | Hubble’s Messier Catalogue, NASA
- M42, M43 | Deep Sky Videos (Brady Haran)
Written by Mark Kilner