The Horsehead Nebula (also known as Barnard 33 in bright nebula IC 434) is a dark nebula in the constellation Orion. The nebula is located just below Alnitak, the star farthest left on Orion's Belt, and is part of the much larger Orion Molecular Cloud Complex. It is approximately 1500 light years from Earth. It is one of the most identifiable nebulae because of the shape of its swirling cloud of dark dust and gases, which is similar to that of a horse's head. The shape was first noticed in 1888 by Williamina Fleming on photographic plate B2312 taken at the Harvard College Observatory.

The red glow originates from hydrogen gas predominantly behind the nebula, ionized by the nearby bright star Sigma Orionis. The darkness of the Horsehead is caused mostly by thick dust, although the lower part of the Horsehead's neck casts a shadow to the left. Streams of gas leaving the nebula are funneled by a strong magnetic field. Bright spots in the Horsehead Nebula's base are young stars just in the process of forming.
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In physics and astronomy, H-alpha, also written Hα, is a specific red visible spectral line created by hydrogen with a wavelength of 6562.8 Å.
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1/23/10 I went to YFOS to go deep in Ha on the Horsehead. I set up and began shooting 10 minute subs with a plan to gather 4 hours of data but the clouds moved in around 10:30. So I only managed to get 11 frames with 8 making it through star shape grading.

Takahashi FSQ-106N @f/5
Astronomik 12nm Ha EOS clip filter
Canon 350da

8 x 600 seconds ISO 1600 (1 hour 20 minutes)