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Wednesday, February 6, 2013

The Truly Great Nebula in Orion

One of the most famous nebulae in the sky is the Great Nebula in Orion, also known by its number in Charles Messier's catalog of deep sky objects as M42. This star formation region is in the constellation Orion, also one of the best known and most easily identified constellations in the sky. Orion is prominently placed high in the south early in the February night sky, and is so filled with wonders that I could spend an entire star tour talking just about it.

The constellation of Orion rides high in the south of a mid-winter's night. The bright red star to the upper left is Betelgeuse, an old star nearing the end of its life. At the bottom right shines Rigel, the brightest star in the constellation and a young, hot blue-white star. M42, the Great Nebula in Orion, is the central, reddish object in the sword, hanging from the three stars in Orion's belt.
M42 is a stellar nursery, or star factory as the metaphor is sometimes used. A region of our galaxy where ionized Hydrogen gas and interstellar dust are collapsing to form new stars. All stars are born is such regions, including our own sun, and evenutually evolve into open clusters whose members are flung out of the cluster through interactions with the gravity of the galactic disk. So, we are all related to brother and sister stars that have since gone their own ways, every one of us.

M42 looks pinkish in photographs because the four, newly born stars in its center, called the Trapezium because of their shape, emit utraviolet light that knocks an electron off of the atoms of hydrogen gas, causing these atoms to become positively charged, or ionized. When the electron recombines with the hydrogen atom this characteristic pink glow is emitted. The color of the glow is usually not evident to the naked eye or in any but the largest telescope, since the light is not bright enough to activate our color vision. But in photographs  even short ones as above, the beautiful pink hue is evident. To the naked eye or small telescope the glowing gas cloud just looks a milky white, still a magnificent view.

M42 has long been one of the most photographed and studied regions of the sky. My friend Eddie Lubat, an amateur astrophotographer in New New Jersey, recently took a photograph of the M42 region that is one of the best I have ever seen. It not only captures the beauty and subtle details of M42 itself, but also much of the surrounding area that is often omitted in pictures of the nebula.

M42 region by Edward Lubat. The M42 nebula itself is the large pinkish area in the center right. The four stars of the Trapezium are here too small to be seen individually, but their combined light is the white glow in the center of the nebula. There is a dark lane of interstellar dust separating M42 from nearby M43 to the center left. Then there is an even larger lane of interstellar dust to the left of M43, separating it from the star cluster, far left, whose light illuminates the "Running Man Nebula", the dark feature in the bright reflection nebula to the left center. Photo by Edward Lubat.

The great gas-flowing features in the area are real, caused by the infalling gas that is forming stars, the outflowing gas that is blown away by the stellar winds of the stars that have formed, and by the collisions of this gas with stationary regions of hydrogen, giving rise to bow shocks that look like bubbles. This region is about 1345 light years away and 24 light years across in the Orion-Cygnus arm of the Milky Way galaxy.

This is one of the objects we spend time viewing and studying both naked eye and in the telescopes on my star tours on cold winter evenings. Come on by and have a look!




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