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Object of the week January 8, 2017 - The Great Orion Nebula, M42 and M43
The Great Orion Nebula
Orion
RA: 05 hours 35 minutes 17.3 seconds
DEC: −05° 23′ 28
Emission Nebula
My first look at M42, the Great Orion Nebula, was with a 3 inch f/15 Tasco refractor in a brightening dawn from my front yard in Arvada Colorado sometime around 1968. I think it was early October because I got up just before dawn and M42 was nearly due south, plus it was pretty darn cold.
I expected to see all the wonderful swirls of nebulosity I’d seen in photographs, but because I hadn’t gotten up early enough the bright sky had washed out all but the very brightest portion around the Trapezium. This wonderful multiple star was the most prominent object in my Tasco. The four tiny stars were very close together and were wrapped in a fading mist of nebulosity that was back lit by an increasingly blue sky. Pretty cool, but it was several years before I was motivated to get up early for an astronomical observation again.
With that first look I unknowingly bettered Galileo’s 1617 observation in which he discovered Theta was a multiple star – he saw three stars – but he never saw any of the nebula surrounding them. He didn’t see any in 1610 either, when he first observed this area, so the telescopic discovery of M42 is credited to Nicholas-Claude Fabri de Peiresc, a French lawyer, who saw it in 1610 and was independently discovered by several others in the coming years. Unfortunately all these observations were forgotten for a couple hundred years, and Christian Huygens 1656 observation was credited as the telescopic discovery of M42 for much too long.
The Orion Nebula has long been recognized as a naked eye fuzzy star, which makes writing of its discovery rather like discussing the discovery of the Moon. Even so, given that Galileo looked at it at least twice (1610 and 1617) without noticing the nebula is a comment on the lack of light grasp his telescopes had, and that perhaps his observing environment was light polluted. Or he observed during a bright Moon. Or maybe his eyes weren’t dark adapted enough. Who can say?
Anyway, Charles Messier made the first decent sketch of M42 in 1769 to "help to recognize it again, provided that it is not subject to change with time" and published it in the 1771 “Memoires de l'Academie”. Because M42 is obviously nebulous to the unaided eye it belongs to a small group of objects in Messier’s list that don’t need telescopic aid to be seen. One conjecture is that he included these objects (M42, M44 and M45 – not to mention M31) along with calling out M43 as a separate object from M42 in order to publish the first version of his list with 45 objects. This would clearly beat the 42 objects on Nicholas Louis de la Caille list of southern objects that was published in 1755. Given human nature this seems likely enough to be true.
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Messier used a surprising variety of telescopes through his career, but his favorite was reportedly a 7.5 inch Gregorian reflector that typically operated at 104x. Reflecting scopes of this era had metal speculum mirrors which had much lower reflectivity than today’s telescope mirrors so it’s likely that the light grasp of this instrument was more like a modern 3.5 inch telescope.
In 1754 William Herschel observed M42 as his first deep sky object, and in 1789 he described it as "an unformed fiery mist, the chaotic material of future suns" as seen through his largely unsuccessful 48 inch scope, which also sported a speculum mirror. He was exactly right, but it would be about a hundred and fifty years before his description could be shown to be the true.
Unfortunately William Herschel didn’t make sketches at the eyepiece so we can’t compare what he saw through his scope, but he clearly saw much more than Messier – or most of us for that matter. However, William's son John made what is still one of the most remarkable drawings of M42/43 in 1838 with his 18 inch speculum mirror telescope from the Cape of Good Hope.
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In 1880 Henry Draper used the 15 inch Harvard refractor to take the first successful photograph of M42, which interestingly shows about as much as Messier’s drawing. This says as much about the state of photography in 1880 as it does about Messier’s observational and sketching ability.
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Although I couldn’t locate exposure data for Draper’s photo it was no doubt a long one given the low sensitivity of photographic plates of his era, so the minimal amount of trailing in the star images shows remarkable tracking accuracy and perhaps represents a stiff neck for Draper’s patience at the guiding eyepiece.
I avoided drawing M42/43 for many years because there's so much detail and so few observable winter nights because of poor weather. I've finally committed to making a decent drawing, and when Judy and I were in Hawaii a few years ago we took her 8 inch f/3.3 scope with us and spent three nights on Mauna Kea sketching - among other objects - M42/43. Frankly, the amount of detail I could see from this wonderful observing location wasn't much less that I'd seen with my 28 inch scope at sea level, so there was still a lot to sketch. This is my rough draft with the 8 inch.
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I've since been working on a drawing of this wonderful nebula with my 28 inch but that will take more time to complete. On the very best nights I've seen a few surprising things and I wonder how many others have noticed:
1. A distinct orange color along the straight edge of the shock front of the Trapezium nebulosity.
2. This same orange color due south of the Trapezium stars, about one Theta Orionis length away.
3. The fine, wave-like texture of the nebulosity inside the area bounded by the Trapezium stars.
4. The red color of the E star in the Trapezium.
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There are too many details to list them all, but I am the most curious about these four. If you haven't seen them, well -
Give them a Go and Let Us Know!
