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Starts With A Bang

Messier Monday: Orion’s second Nebula, M43

The Great Orion Nebula is so great, it needed a second Messier object all to itself!

“Be not afraid of greatness. Some are born great, some achieve greatness, and others have greatness thrust upon them.” –William Shakespeare

Of all the spectacular deep-sky objects in our heavens, from the bright to the ultra-faint, only one is so large, so massive and so close that it appears in many different locations and forms across the sky: the giant star-forming, molecular cloud complex in the constellation of Orion. In fact, not only are multiple famous nebulae a part of it, including the horsehead nebula, the flame nebula and Barnard’s loop, but an incredible three unique Messier objects as well!

Image credit: Tenho Tuomi of

The faintest of the three is today’s object, Messier 43, also known as De Mairan’s Nebula after its discoverer, and is actually impossible to miss if you’re checking out one of the brightest and most clearly visible nebulae in the entire sky (even to the naked eye), the Great Orion Nebula, M42.

Here’s how to find its slightly lesser-well-known companion.

Image credit: me, using the free software Stellarium, via

A few hours after sunset — although this will happen earlier and earlier as winter comes on — the unmistakable constellation of Orion will rise in the eastern portion of the sky, heralded by the incredibly bright stars Betelgeuse (in red) and Rigel (in blue), along with the three bright, blue stars of Orion’s belt.

Just south of the belt, however, is a bright, fuzzy region sometimes called Orion’s sword (but we know better), and if we focus our attention there, Messier 43 will be within our reach.

Image credit: me, using the free software Stellarium, via

There’s a very bright star that shines on the south side of the nebular complex there, ι Orionis, and two fainter “light clumps” a little to the north. Through even a pair of basic binoculars or the most primitive telescope you can get your hands on, the views of this region are clear and magnificent. And with long-exposure, multi-wavelength photography, they can become downright spectacular!

Image credit: me, using the free software Stellarium, via

Of course, the “great” nebula is the main part of it, and that’s Messier 42. Further to the north, in blue, is what’s known as the Running Man nebula, after the shadowy appearance of the dust lanes in NGC 1977. But do you see how there’s a dark dust lane dividing the great nebula into two parts, one of which is about ten times larger than the other?

Image credit: Wikimedia Commons user RawAstroData, via

That smaller part is what Messier 43, or De Mairan’s nebula, actually is! According to Messier himself:

Position of the little star surrounded by nebulosity & which is below the nebula of the sword of Orion.

But perhaps more interesting is to look at what the first long-exposure images of this nebula — clearly distinct from its larger, more easily viewed counterpart — allowed us to see:

Image credit: Andrew Ainslie Common (1841–1903), 1883, of the Orion Nebula along with M43, clearly separated.

and to combine that with De Mairan’s initial (incorrect, but still interesting) description of what he thought he was looking at:

Finally I will add that close to the luminous space in Orion, one sees the star d of Huygens currently (1731) surrounded by a brilliance very similar to that which produces, as I believe, the atmosphere of our Sun, if it were dense enough & extensive enough to be visible in Telescopes at a similar distance.

As it turns out, there are stars in there, and there are the same elements as are found in the atmosphere of the Sun. But there’s much more to the story than that!

Image credit: Amy Harmon and Scott Matthews / Adam Block / NOAO / AURA / NSF, via

The brightest star in there is a young, hot and ultra-massive blue star, most probably destined to go supernova in only a few million years. The “red” color in the image above is hydrogen gas that’s been ionized, where the electrons are recombining with the nuclei to emit that characteristic color at exactly 636.5 nanometers.

At the center, you see that the color changes to blue, and that’s because of the neutral gas-and-dust reflecting the blue light from the central star itself!

Image credit: Nigel A. Sharp / NOAO / AURA / NSF.

A closer inspection reveals that there are actually a great many young stars that have formed inside, but it’s only the most massive, most luminous ones that dominate. Deep within the dust, here, it’s probable that there are at least hundreds of additional stars simply beyond our power to view them.

Furthermore, what’s incredibly interesting is that the bright, central star would have passed within just 109 light-years of us some 9 million years ago based on its current orbit, making it one of the brightest stars in our sky. But it probably didn’t exist that long ago, having formed much more recently than that!

Image credit: © 2006 — 2012 by Siegfried Kohlert, via

It’s hard to tell with all the dust in there, but this is still an extremely active area of star formation, with plenty of protostars and the gas that’s continuing to grow them present.

To get a better handle on what’s happening in Messier 43, let’s take a look in the infrared, courtesy of Spitzer!

Image credit: NASA / JPL-Caltech / Spitzer Space Telescope, modifications by me, via

Or, if you prefer going a little farther into the infrared, check out the view from WISE.

Image credit: NASA / JPL-Caltech / WISE.

This region is clearly quite saturated, giving off a lot of infrared emission in many different wavelength bands. This is most likely due to the fact that there’s not only a ton of gas and dust of many different temperatures present, but also hot young stars, proto-stars (in the orangish-red colors), and transition regions between these many different facets.

If we just look in visible light, we’re unlikely to appreciate the full suite of this nuance.

Image credit: Orion42, via

But a multi-wavelength view from Hubble — extending into the near-infrared — can accomplish something incredible, allowing us to see not only the full suite of what our eyes can, but also to give us a window into the dusty nuances that elude the visible-light portion of the electromagnetic spectrum.

Image credit: NASA, ESA, M. Robberto ( Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team; full image available at

Whereas the full, main Orion Nebula has many stars illuminating it, there’s only one primary star giving rise to this one, hence it’s often known as either the little, small or miniature Orion Nebula.

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But if we decide to dive in to the regions away from the center, where collapsing protostars rule the roost, Hubble can give us a glimpse into that like nothing else.

Image credit: ESA/Hubble & NASA.

And that’s one of the youngest, closest young regions of star formation to us, where the next generation of solar systems are presently being born!

That also takes us to the very end of our long-running, 110-object saga of Messier Monday here on Starts With A Bang! If you missed even a single one, take a look back at all our previous 110 Messier Mondays here:

Next week, we’ll have a special retrospective on all 110 objects, and then the next Monday will bring something entirely new! I hope you enjoyed it, and stick around; there’s plenty of wonders of the Universe to come!

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