Many know the Great Orion Nebula (M42) in Orion’s Sword as a bright diffuse nebula — a glowing cloud of cosmic gas illuminated by the Trapezium star cluster. But the Orion Nebula also has a dark side, formed by its lanes and clouds of dust. They frequently avoid scrutiny, as the surrounding brightness tends to steal the show. But you can easily train the eye to reverse the view. It’s an illuminating experience that reveals a dark dimension to this familiar object.
M42 is the closest massive star-forming region to Earth, making visual studies of its intricate play of light and dark available to even small telescope users. It’s most readily identifiable dusty realms lie between the bright central Huygens region and the neighboring De Mairan’s Nebula (M43). The latter is actually part of the same gas cloud that comprises M42; it only appears isolated due to intervening lanes of cosmic dust blocking the light of bright nebulosity beyond. “Nowhere else in the heavens is the architecture of a nebula so clearly displayed,” writes Garrett Serviss in his 1901 Pleasures of the Telescope.
Let’s investigate a few of the more obvious dark nebulae. The most pronounced structure is popularly known as the Fish’s Mouth. The Mouth juts into the eastern side of the Huygens region (the Fish’s Head), where the 4th-magnitude Trapezium star cluster represents one of the Fish’s eyes. The bright parts of the Huygens region lend intensity to the darkness within, owing to a great difference in contrast.
This weblike network is the result of fine wisps and patches of dark nebulosity, superimposed on the scene. If you concentrate solely on the darkness and neglect the bright nebulosity, a powerfully dark image appears. It is a mighty silhouette with a form that can be traced throughout the entire region. Don’t rush the view. The longer you look, the more apparent the dark nebulosity should become.
To view this region, I use as high a magnification as possible; that way, even when seen through my 3-inch Tele Vue refractor, fine details manifest in the darkest of spaces. For instance, at a glance, the Fish’s Mouth looks like an inky thumbprint. But under powers of 250x to 300x and a prolonged view, the darkness appears segmented into three main parts oriented west-east. With south up, (1) the western section looks like a letter n, with finer threads of darkness extending its legs to the north; (2) the middle section appears E-shaped with two tiny bright patches peeping through its arms; and (3) the eastern section surrounds an O of bright nebulosity, which is so small it looks essentially stellar.
A dark limb of nebulosity extends to the southeast from the lips of the Fish’s Mouth. The limb is comprised of several tendrils of darkness, like long grooves of bark. Directly opposite the branch to the northwest is a more delicate wash of darkness. With some imagination, this region resembles the palm of a narrow hand with delicate lines.
This type of wash also caresses the western curl of M43’s embryonic form. One thick branch of darkness stretches north-south along the eastern rim of M43 and creates the nebula’s embryonic form. See if you can detect its subsidiary branches, as well as small irregularities along the main branch’s eastern side that pinch into M43.
Now return your attention to the bright Huygens region. You want to look for a dramatic “ink spot” that lies at the base of a large hedgerow prominence of bright nebulosity erupting to the southwest of the Huygens Region. If you look carefully, you’ll find long wisps of darkness extending from it to the south. The longest penetrates the Orion Bar, a wall of dense gas and dust forming the southwest wall of the bright Huygens Region. A parallel finger of darkness lies just northeast of the long wisp.
Finally, see if you can see the dark well in which the Trapezium lies. Stellar winds from the four hot massive Trapezium stars have created a vast cavity in the surrounding dust and gas, allowing us to see them clearly.
As you explore the dark Orion Nebula, keep in mind that you are exploring territories few have bothered to visually tread — at least in fine detail. As always, send what you see or don’t see to sjomeara31@gmail.com.
