How to See the Orion Nebula in 3D

By: Bob King December 17, 2014 9

Add another dimension of viewing to winter's favorite deep sky object, the Great Nebula of Orion.

Nature at its grandest — The Orion Nebula, located in Orion's Sword directly below the familiar Belt, is an enormous stellar nursery 24 light years across located about 1,350 light-years from Earth. Newborn suns within the nebula's dusty folds set dust and gas alike aglow.
*HST / NASA / ESA*

The Orion Nebula is arguably the centerpiece of the winter sky. This bright, richly-detailed blossom of glowing gas and dust invites repeated observation. How many of us have pointed our telescope or binoculars in its direction five, six, or even ten times a season?

After the planets and Moon, it's the deep sky object to show family and friends, provided we can coax them into the cold.

Faintly visible with the naked eye and revealing a distinct shape in binoculars, a telescope lays bare the nebula's breathtaking whorls of nebulosity that unfurl from the brilliant Trapezium cluster blazing at its core.

Most sky objects appear pasted against a two-dimensional sky because human stereo vision can't sense depth over cosmic distances. Our eyeballs would have to be light years apart to accomplish that feat. But clues to the sky's hidden third dimension are out there. If you've ever watched one of Jupiter's moons cast its shadow on the planet's cloud tops, the sensation of depth is almost visceral.

Simple anatomy of a nebula — Sketch of the Orion Nebula, also known as M42, viewed at low magnification through a 15-inch (37-cm) telescope. We see its basic features including the dark nebulosity nicknamed the Fish's Mouth, the bright quadruple star **Theta 1 Orionis**, better known as the Trapezium, and the adjacent nebula M43.
*Bob King*

With a little help, we can sense the depth in the Orion Nebula, too. The easiest place to begin is the thumb of dark nebulosity, nicknamed the Fish's Mouth, located between the bright multiple star, the Trapezium, and adjacent nebula M43 to the north. Through a small telescope the shadowy shape appears opaque, but a larger instrument clearly shows its mottled texture as light from bright nebulosity in the more distant background punches through.

FIsh's Mouth or Dementor? — In this close up image, the spectacular texture of the Fish's Mouth is evident as light from bright nebulosity in the background filters through gaps in the dark veil. The Trapezium, the Orion Nebula's key source of illumination, is seen at center right.
*HST / NASA / ESA*

The 3D effect is dramatic on a dark, moonless night using high magnification. The first time I tried this, I spent the next 20 minutes completely absorbed while visually thrashing through a dark forest of nebulosity I never knew existed. When seen in its entirety, the Fish's Mouth looks a lot more like a Dementor in the Harry Potter movies. Creepy, but utterly moving.

Studies of the structure of the Orion Nebula have shown that radiation pressure from the hot, young Trapezium stars has hollowed out the core of the nebula and literally "blown a hole" through the dust and gas, allowing us to peer inside the cloud to stare this clump of fresh-faced suns in the face.

Ruffled sheets in Orion's core — A 3D representation of the folded, glowing surface of the Orion Nebula shows the Trapezium multiple star hovering in a "valley." To the left is a steep "cliff" of nebulosity that faces the stars and fluoresces in their light to form the bright pink, bar-like feature that borders the bright inner or Huygenian Region of the nebula.
*C.R. O'Dell and Zheng Wen with addition of Trapezium stars and annotations by the author*

Using infrared and visible light observations from the Hubble Space Telescope and ground-based imagery, astrophysicists C.R. O'Dell and Zheng Wen (Rice University) created a 3D model of the inner surface of the hollowed out core of the nebula. Their model shows that the Trapezium stars hover above a wrinkled, shallow "valley" not far from a steep "cliff." Light from the stars ionizes the nebular gases and sets them aglow. According to research by O'Dell, the visible nebula we see is little more than a popped blister .08 light-years thick on the surface of the Orion Molecular Cloud, a vast complex of nebulae host to ongoing star formation.

Over the cliff into the valley of the stars — When you put some "meat" on the diagram above, you get something like this — a frame from the Orion Nebula fly-through movie based on data from C.R. O'Dell, Zheng Wen, and David Nadeau with additional contributions from Greg Bacon and the American Museum of Natural History / Rose Center for Earth and Space. Tiny, teardrop-shaped objects are "proplyds," or protoplanetary embryos. Click to watch the fly-through.

So what do we see when we put eye to eyepiece? The bright, green-hued Huygenian Region, named after the 17th century astronomer, Christian Huygens, who first studied it in detail, forms the valley's floor. The cliff is the bright bar-like feature southeast of the Trapezium.

Imagining three dimensions — The bright, inner Huygenian Region of M42. The next time you look at the nebula, imagine the dark Fish's Mouth overhanging the bright nebula. The bright bar or "cliff" towers above the Trapezium, which is nestled in a valley of its own creation. The brightest star in the Trapezium, named Theta 1 Orionis C, is responsible for a large proportion of the nebula's light. It's the most massive of the four and one of the most luminous stars known.
*Patric Knoll*

Wishing you happy travels to another dimension of one of the most beautiful objects in the night sky.

Want more nebulae? Let Sue French guide you to more Deep Sky Wonders!

Comments

Anthony Barreiro

December 17, 2014 at 3:24 pm

Thanks Bob, this is fascinating. In terms of seeing nebulae in three dimensions, I had an aha moment when I learned to see a dark nebula as a cloud of dust and gas blocking the light from the stars and bright nebulae behind it, rather than simply as a blank dark area. This helps me understand what is closer and what is farther away, and provides the third dimension of depth.