Jimmy Westlake: See the great nebula in Orion
January 21, 2014
Steamboat Springs — Anyone who has ever looked up at the starry, winter sky has seen it, although they might not have known what they were looking at. The three bright stars in a neat little row stand out among the other stars like a neon sign.
Some folks mistake this asterism for the Big Dipper. Some call them the Three Marys, others, the Three Wise Men, but officially, these three stars mark the Belt of Orion, the Hunter. From left to right, their names are Alnitak (the Girdle), Alnilam (the String of Pearls) and Mintaka (the Belt).
Three fainter stars below the belt represent Orion's sword, hanging at his side. When comet hunter Charles Messier aimed his telescope at the middle star in Orion's sword in 1769, he thought he might have discovered a new comet. The object certainly had the fuzzy, cloud-like appearance of a comet.
To Messier's dismay, however, the object turned out not to be a comet. Instead, he had made an independent discovery of what we now call the Great Orion Nebula. It became the 42nd entry in Messier's famous catalogue of comet look-alikes and is known today as Messier 42, or just M42, for short.
M42 has since become one of the most photographed and carefully studied deep sky objects in the heavens. It is the closest and best example of an ionized cloud of hydrogen gas in space called a diffuse nebula.
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Ordinary binoculars or any small telescope will reveal the fuzzy appearance of M42. It resembles a cluster of streetlights seen through a thick fog. The source of the light illuminating the nebula is a quartet of very hot, luminous stars collectively called the Trapezium. A small telescope at medium power should show the four stars of the Trapezium.
NASA's Hubble and Spitzer space telescopes have helped unravel the mysteries of this colorful cloud of gas. The Great Orion Nebula is a stellar nursery where thousands of new stars and planetary systems are condensing from the interstellar gas. In a few million years, a cluster of young stars will burn where we see the nebula.
Recent measurements have nailed down the distance to M42 as 1,350 light-years. The visible portion of the nebula measures about 24 light-years across and is only a very small portion of a much larger dark cloud known as the Orion GMC, or giant molecular cloud.
Wherever bright stars illuminate the dark corners of the Orion GMC, we see a diffuse nebula, like M42. Other regions of the cloud show up as the Horse Head Nebula, the Flame Nebula, M43 and NGC 1977.
No optical aid is required to spot the Great Orion Nebula, although binoculars will enhance the view. Look just south of the three familiar stars of Orion's Belt, at the middle star of the fainter trio that forms the Hunter's sword.
Don't expect to see the vibrant reds and blues shown in long-exposure photographs of M42. At night, the human eye's color receptors are not activated, so even the colorful Orion Nebula appears a pale gray.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out "Jimmy's 2014 Cosmic Calendar" of sky events on his website at http://www.jwestlake.com. It features 12 of his best astrophotographs and a day-by-day listing of cool celestial events that you and your family can enjoy watching in 2014. Proceeds from the sale of Cosmic Calendars help to support the CMC SKY Club.