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Astronomical Observatory: Cool Images

Astr112 Photography Projects, Spring 2006

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Horsehead Nebula, Ryan Poling

Horsehead Nebula

The Horsehead Nebula is actually two nebulae: a diffuse emission nebula, and a dark nebula in front. The dark nebula gives this object its distinctive horsehead shape by blocking the light from the diffuse nebula behind it. The diffuse nebula is the emission nebula IC 434 (which is excited by the star Sigma Orionis), while the dark nebula in the foreground is Barnard 33. Actually part of a much larger nebula, this feature is located right next to Zeta Orionis, the easternmost star in Orion's belt. UV radiation from Sigma Orionis bombards IC 434, causing it to emit a hydrogen glow. It was first discovered on a photographic plate in the late 19th century and is a very active site of low-mass star formation. The streamers emanating from either side of the Horsehead are magnetically-ejected trails of hydrogen gas. It is approximately 1600 light years away and has an apparent angular size of 6'x4'.

Unfortunately, this image is rather grainy due to limited exposure time. However, we can still see some very interesting features. The emission nebula that forms the background to the horsehead is a large cloud of gas energized by Sigma Orionis. UV radiation from the star collides with gas particles in the cloud, causing the particles' electrons to step down an energy level and emit a burst of pinkish-red light. The dark nebula in front (the nebula that forms the horsehead shape) then blocks some of this light from reaching us, much like placing a piece of black construction paper in front of a fluorescent light. The object itself is 2.8 ly across.

"The Nine Planets"

Astronomy Picture of the Day (APOD)

NOAO -- The Horsehead Nebula

Right Ascension (J2000) 05:41:01.2
Declination (J2000) -02:27:43
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 60 seconds in C, 300 seconds in BVR
Date observed March 21, 2006 (C)
March 14, 2006 (RV)
March 16, 2006 (B)



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