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