GREAT ORION NEBULA (M42)

2015 February 21, 10:47 p.m. EST (Feb. 22, 03:47 UT)
Rosemary Hill Observatory • Bronson • Florida

Brief Object Notes: The Great Orion Nebula in Orion's "Sword" is easily the most spectacular nebula visible with amateur scopes. Most deep sky nebulae (or galaxies) often appear as faint smudges. Nevertheless, under dark skies with a moderate size telescope, this magnificent object can show beautiful nebulous structures especially if the instrument has good contrast. In fact, the nebula is part of an enormous structure (The Orion Molecular Cloud Complex) that is the birthplace of new stars. The central region, the large cavity of a giant molecular cloud, shows a grouping of four hot, young stars (age one million years) called the "Trapezium." However, careful observers can sometimes see one or two more.

Visually the nebula spans about one degree (two moon diameters) corresponding to a linear diameter of roughly 24 light years at its distance of approximately 1,340 light years. Surprisingly this nebula was not known before the telescope but was only catalogued as a star (Theta Orionis)!

Photograph Below: Taken with a 5-in., f/5.2 refractor under hazy skies. The photograph shows reddish colors from glowing hydrogen. However, the eye has difficulty seeing color of faint objects. The eye also is more sensitive to green than red. So, observers typically see the nebula as grayish possibly tinged slightly greenish (from glowing oxygen) rather than the colors in the photo below. Historically astronomers did not know what caused the greenish tinge and invented a new element, "nebulium" to explain this effect! Put cursor over image below to see a representation of what the eye might see (grayish green). The central region is also overexposed so the Trapezium is not visible. However, about one hour before, under poor transparency and seeing conditions, I snapped a less exposed image (below right) revealing the four Trapezium stars.

PUT CURSOR OVER IMAGE FOR CORRESPONDING VISUAL IMAGE AS THE EYE MIGHT SEE THE ORION NEBULA
— ALSO CLICK IMAGE TO ENLARGE

Photo Details 2015 Feb. 21, 10:47 p.m. EST TeleVue 127 mm, f/5.2 APO Refractor, Foc. Len. 660 mm Camera: Canon DSLR EOS 5D II, Exposure 15 sec, f/5.2 (ISO 3200)

OBSERVATIONAL CHALLENGES What color is the nebula with your eyes? Can you see the Trapezium? How many stars can you resolve in the Trapezium? Can you trace out and see details in the beautiful nebula filaments and wisps? QUESTION: What object in the southern celestial hemisphere would vastly outshine the Orion Nebula if placed just as close as the Orion nebula? Hint: Object is not in the Milky Way Galaxy but a member of a nearby galaxy. ANSWER HERE Orion Nebula's Trapezium This an enlarged & less exposed region of the Orion Nebula's core 2015 Feb. 21, 9:54 p.m. EST Exp. 20 sec, f/5.2, ISO 1600) (Sky Transparency/Seeing Poor)

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Images © 2004–2015 H.L. Cohen
Email Cohen followed by @astro.ufl.edu
Last updated 2015 May 18