Star-Trapping in Orion’s Trapezium

Join me for a high-power ride as we seek out baby stars and clotted clouds within the heart of the Orion Nebula. 

Heart of the Beast

Our destination tonight will be the bright inner core of the Orion Nebula (circled) centered on the Trapezium multiple star.
Rawastrodata / Wikipedia CC BY-SA 3.0

When you want to catch an animal, you choose the right trap, bait, and location. Amateur astronomers also make choices on how to best bag their stellar quarry, choosing the appropriate time, telescope, magnification, and sighting technique.

If we're lucky, the sky will clear when we have the night free. Seeing might even be good, yielding the sweet and steady views so essential for making out delicate details like a spiral arm or planetary nebula's central star. One of the great ironies of astronomy is that we gaze at enormous objects millions or even billions of miles across that are easily reduced to mush depending on how the wind blows.

Last week, the wind blew like crazy, but star images still glared motionless as mannequins. Times like this call for special projects, and one of my favorite over the years has been to explore the innermost sanctum of the Orion Nebula at high magnification. You'll sometimes hear it referred to as the Huygenian Region after the 17th-century astronomer Christian Huygens, who first studied it in detail.

Orion's Firepit

The Theta-1 (θ1) Orionis multiple star is better known as the Trapezium. Its four bright stars are easily visible in a 3-inch telescope. A 6-inch will show two additional stars, E and F, both 11th magnitude. G and H require a large amateur instrument.
Jerry Lodriguss with additions by the author

Orion's a different beast at 200× and up. The clash of dark and bright nebulosity in the heart of the nebula is pure turmoil, as if the observer were cast into an oncoming  thunderstorm. This is especially true where the finger-like dark nebula dubbed the Fish's Mouth spreads partway over the glowing nest of stellar eggs called the Trapezium. Using 357× and averted vision, what appeared to be opaque dark nebula at lower magnification gave way to ragged clouds and dense black knots silhouetted against the brighter background nebula in glorious 3D. 

On nights of average seeing, four bright stars in the shape of a trapezoid give the bright quadruple star its name. But when the air settles down, a 6-inch scope magnifying 125× or higher will bring the fainter components E and F into view, turning the quartet into a sextet. Keep watch on components A and B at the narrow end of the figure. They're both eclipsing binaries: V1016 Ori ranges from magnitude 6.7 to 7.7 over a period of 65 days and BM Ori from 7.9 to 8.7 every 6.5 days. With its much shorter period, it should be relatively easy to catch BM at both maximum and minimum sometime this season.

Eggs in a Nest

Intense ultraviolet light from the massive, young stars of the Trapezium excites gases such as hydrogen and oxygen to glow within the heart of the nebula.
Jerry Lodriguss

On occasion, I've noticed additional fainter stars buried within the dabs and folds of the central nebula. Although some are listed as 10th and 11th magnitude, they appear much fainter because they necessarily compete with the glowing gases. That gives them the same fragile, barely-there appearance of the central stars of some well-known planetary nebulae such as the Owl (M97), the Ring (M57), and the Cat's Eye (NGC 6543). Just as those planetary stars tantalize and test the limits of our vision, so do these tiny sparks within the nebula. I was able to discern five of these in the immediate vicinity of the Trapezium and an additional half-dozen or more a bit further afield.

M42 is Cooking Up a Star Cluster

This color composite mosaic image of the central part of the Orion Nebula is based on 81 images obtained with the infrared multi-mode ISAAC instrument on the ESO Very Large Telescope (VLT). The famous Trapezium stars are seen near the center of a rich star cluster still well-hidden from visual observers of the 21st century by dust. One day, the cluster will make for a magnificent sight as the nebula fades.
ESO / M.McCaughrean et al. (AIP)

All these suns belong to the Trapezium Cluster, which is mostly hidden for now, but will one day be considered one of the finest clusters in the sky. There are literally thousands of stars buried within the Orion Nebula. Only a few are visible visually and each makes for an excellent challenge while giving an observer a chance to visualize the Great Nebula's future. Until Orion's dust is consumed in the making of more stars and blown away in their stellar winds, only infrared light reveals the cluster future amateurs will drool over.

Nearly every single star within the nebula's confines bears a variable star designation. Most belong to the IN class ("I" for irregular, and "N" for association with a nebula). Many of the stars in the nebula are 300,000 years old or younger and still accreting material from their surroundings. Differences in the accretion rate can set off stellar flares that temporarily boost a star's brightness. Young stars are typically fast rotators, generating strong magnetic fields that create large and active starspots that can cause a star's light to vary with its rotation.

Newborn Tantrums

Almost every star in the green, glowing core of the nebula centered on the Trapezium is a variable star (click to enlarge). Newborns like these often undergo irregular changes in their brightness before they settle into stable lives on the main sequence. I've added the approximate location of the dark nebula called the Fish's Mouth to the map.
Bob King, Source: Chris Marriott's SkyMap

Sometimes the very dust that the star engorges to grow can rob it of light, causing the newborn to briefly fade. If you regularly study the appearance of these several stars in the Huygenian Region, don't be surprised if one or another becomes either easier or more difficult to see. Growing up, whether human or star, has its bumps!

A side benefit in seeking these newborns is getting to know the billows and pillows of glowing nebulosity that encircle the Trapezium. I've always believed that if you name something, you'll come to know it, so I've included several of my own fanciful names for various parts of the inner region. Names serve as guideposts, places to stop and get to know. They help us see more clearly an otherwise complex nebula that might be perceived as an assortment of shapeless blobs.

Emergent Stars

To make my observations of the Huygenian Region, I used a 15-inch (37-cm) reflector at 286× and 357× and sketched the result using Photoshop. I labeled all the stars I could discern in good seeing. Most are variable stars such as V1399 Orionis. The "P" stands for astronomer P. Parengo. Nicknames are my own. South is up.
Bob King

In excellent seeing using my 15-inch reflector at 286× and 357×, I began at the Trapezium for a most satisfying look at all six stars, each appearing crisp and white-hot. Then I carefully searched for additional stars eking through the dense cushions of glowing gas nearby. The easiest was LQ Ori (see sketch above) followed by V1399, MT, and LV. LV was tricky because it's embedded in a tiny knot of nebulosity — a cool sight. V494, located just east of V1399 was seen fleetingly. All the others were fairly easy.

Once you've poured over Trapezium area, follow the Fish's Mouth east into the deep darkness of what can only be described as the "black lagoon" of nebulosity separating M42 from the smaller nebula M43. I absolutely love rooting around here. The longer you look, letting your eyes adapt to the dusty darkness, the more texture the "darkness" will divulge. One of my favorite objects is an extremely faint star near the center of the lagoon just east of the Fish's Mouth. Here the dark gas seems to absorb all light and appear blacker than the blackest night. But deep inside flickers a single tiny light, the proverbial candle in the dark. Don't miss it.

Fantastic Voyage

Here it is in all its chaotic magnificence! The Trapezium shines just left of center.
NASA / ESA / Hubble Space Telescope

Larger scopes are best for deep exploration of the eye of the nebula, but even a 6-inch on a good night using a magnification of 150× or higher, concentration, and averted vision can show much more than you'd expect. Don't be afraid to go the highest magnification the seeing will allow. Sometimes amateurs, including myself, are too conservative when it comes to magnification. Go nuts. Like the Orion Nebula, you only live once.

Explore the Night with Bob King, Observing
Bob King

About Bob King

Amateur astronomer since childhood and long-time member of the American Association of Variable Star Observers (AAVSO), Bob King also teaches community education astronomy and writes the blog Astro Bob. The universe invites us on an adventure every single night. All we need do is look up. My new book, "Wonders of the Night Sky You Must See Before You Die", a bucket list of essential sky sights, just published and available at Amazon and BN.

27 thoughts on “Star-Trapping in Orion’s Trapezium

  1. AlphaCentauri

    Great article! I was looking at the nebula with my 130mm reflector the other night, a not so good night, but it was the first time I’d pointed the reflector at that nebula. All the other times were with my smaller refractor. The reflector showed me the green color of the nebula and the Trapezium pretty clearly, even though it was a crummy night.I’m looking forward to using that scope with the barlow I’ve purchased to get it up to 144x, maybe try 216x on that nebula, as well as Jupiter and Saturn (I’ve been watching Venus as often as possible). We’ve had a lot of cloudy nights in WV the last month or so and. I’ve only had my reflector since a little before Christmas.

    1. Bob KingBob King Post author

      Thanks Alpha! Way to make the best of what few clear nights we get sometimes. That scope in good seeing with 150x or so should split the Trapezium into 6 stars. Good luck!

  2. Aqua4U

    As usual, I find your writing exceptional and a cut above! During my last observing session I used my f3.6 12 1/2″ reflector to view M42 and was amazed at the details in the dust clouds. This, during a period of good seeing, with the best views as Orion reached the zenith from my latitude. Still… my f3.6 only shows 4 stars in the Trapezium clearly. Using averted vision there are only hints of others. The upshot is… in longer focal length telescope you might see more stars, but with a faster scope contrast sensitivity can makes the dust clouds really stand out,.. especially with the right filter.

    Note to self: Buy a 2X & 3X Barlow lens!

    1. Bob KingBob King Post author

      Hi Aqua,
      Thanks for the kind words. I appreciate that. Both the dust clouds and inner nebula are so rich with texture I could barely do them justice in my sketch. How is your alignment on the 12.5-inch? It should definitely do a good job on the sextuple in good seeing even at that focal length so long as you’re in the 100x and higher range. They’re pretty easy in my 15-inch which is an f/4.5. A Barlow should get your there no problem.

      1. Aqua4U

        Yes, my 12 1/2″ f3.6 Newtonian does a great job showing off details in dust clouds too! As you know the main problem with fast focal length reflectors is that they are very susceptible to any misalignment. I check collimation prior to all viewing sessions on my home made scope because I drive 10 miles up a steep and bumpy mountain road to get to my star gazing spot. Lately, as I’ve tightened and stabilized my truss mounted OTA, those adjustments have become much less frequent.

        I wrote a couple articles for UT several years ago about my ATM adventures. (Very amateurish!) The images below are from that period. There have been several improvements since then. For example, now there is black tar paper surrounding the secondary cage to block stray light, the insides got painted flat black, the 2X4’s on the base got shortened making it easier to load and unload in my van, better finder scope mount… and more. Want to take a look?

  3. Ramon-Centeno

    Hey man. Grettings from El Salvador, Central America. Why when i watch trought my 4.5 dob reflector i see all in grey? When i shot the Orion nebulae is all black and white.

    1. Bob KingBob King Post author

      Hello Ramon,

      In smaller telescopes, the nebula will appear grey. Under dark skies with your eyes dark-adapted, it might show a little green in the bright center part. To see the color best though, you need a 6-inch or larger telescope.

  4. Steve

    Great article Mr. King, I get to observe it through a 14″ Schmidt/Cassegrain but have not had the scope time to do detailed observing. (volunteer at the George observatory in the Houston area). By the time all the guests are gone it’s late and I’m tired.
    Reading this article, I need to get out there on a guest less night and do some personal time.
    The nebula is one of the objects I choose to show my guests this time of year because it is so beautiful. Lots of ahs and oh wow’s. I love it so I can only imagine how much more appreciation I would have with deeper investigation. looking forward to it.
    Question. Why a barlow?
    Thanks Bob, keep up the great work.

    1. Bob KingBob King Post author

      Thank you so much, Steve. And I hope you do find that time to explore the nebula in depth. Orion is so multi-satisfying, both at low power, especially for those new to it, and for seasoned observers who make a point to stop by for a visit every fall and winter.

  5. 1158mikulichj

    Thank you for this article and the comprehensive explanation of the heart of this great deep sky object. I was just exploring it the other night and even with a 130mm reflector the nebula still amazes.

    1. Bob KingBob King Post author

      Hi J. Mikulich,

      Thank you for your kind words. I can only concur about the nebula being beautiful “even with a 130mm.” For many years, I used the same size telescope (6-inch) to explore the nebula. Never got tired of it back then, either 🙂

    1. Bob KingBob King Post author

      Hi Capella80,

      You can tell because M42 is by far the brightest patch of nebulosity, and in its center, you’ll see four bright little stars closely bunched together – that’s the Trapezium. Those other nebulas in the area — NGC 1977, etc. — are located north of M42 and are considerably fainter.

          1. Bob KingBob King Post author


            Sounds like your light pollution is bad. I can understand why you’d only see the central star in M43. When the moon is out of the sky, February’s such a wonderful time for viewing the Orion Nebula, I would recommend a road trip to darker skies. You might compile a list of other objects on your winter wish list to make the most of the time.

  6. Capella80Capella80

    Never mind, the Bottle isn’t 7, I was thinking about the Bottle when the full moon is out. It is actually sound the 5-6 range. Still, not the best. The milky way is invisible. For a short period I lived in an area with bortle 2 50 miles out of town. Thanks anyways. And also, if I was seeing Ngc 1973 etc., It would have been in the messier catalogue.

  7. Graham-Wolf

    I’m adding my praises of you, Bob, to that bof the many others above.

    The trapezium in the Orion Nebula, is always a good accuity and optics test that we Kiwis regularly practice here in NZ. It’s always been a favourite at public star parties!
    However, It takes great optics, high power, and sizeable aperture to get to 8 stars and beyond. I can also recommend the chart by Robert Burnham from his historic tome “The Celestial handbook….”. Obligatory reading, for sure.

    I’m aware it was a favourite of “dear old Patrick”… Sir Patrick Moore, and he certainly enjoyed observing it when he (far too infrequently) visited NZ in the 80s and 90s… the book AND the object.

    Thanks, Bob, for giving so much joy to your readers, by bringing the Trapezium back to life again… no better guy out there, to do it!

    Regards from 46 South, NZ.
    Graham W. Wolf

  8. Roger HansonRoger Hanson

    Interesting. I know this isn’t very scientific, but, when Battle Star Gallactica came to the end of its voyage it located a star in the middle of a dark void. Kind of like the Fish Mouth. Sorry, had to say it… Great read.

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