The Horsehead Nebula (cataloged as Bernard 33) is a dark nebula in the direction of the constellation Orion, the mythological Greek hunter, as well as both a recognizable and influential constellation of stars to nearly every ancient civilization. The Horsehead Nebula appears* within a much larger active star-forming H II region called IC 434. The Horsehead Nebula is located very near to the bright star Alnitak, part of the 3 stars that make up Orion's famous belt. Note on the left side of this image you can see some faint stray beams of light reflecting from Alnitak.

The Horsehead Nebula is relatively very near to earth at only 1375 light years away or 8 thousand million million miles. It is extremely difficult to see visually through any telescope because of its extreme darkness, but it is also one of the most easily identifiable objects in photographs due to its resemblance to a horse's head. It is so dark that it was not even discovered visually, but on a photographic plate taken in 1888 by female Scottish astronomer Williamina Fleming.

Furthermore, the dark nebula, composed of dust and gas, is part of the much larger Orion Molecular Cloud Complex where star formation is taking place. Notice that there are very few stars visible in the dark part of the nebula, compared to the brighter red parts, since the opaque gas and dust blocks starlight from behind. There is some deep red parts of the dark nebula caused by ionized hydrogen gas behind the nebula. Most of the red ionized hydrogen gas receives its energy from nearby bright star Sigma Orionis just below the left side of the image as evident by a bluish glow at the bottom. Sigma Orionis is one of the brightest members of a young open cluster of stars surrounding the Horsehead and IC 434.

Most stars in this image are behind the nebula, hence they appear red in color, due to the nebula acting like a red filter. The red parts of the nebula form an emission nebula in that it is emitting its own light due to the ionized atoms of hydrogen being excited by UV light emitted by nearby young stars. Note the “sunrise” taking place at the top of the Horsehead*; if that star were just a smidgeon lower, it’s light would likely be blocked by the dark nebula.  It is possible that the “nose” of the “horse” will eventually be pinched off, begin collapsing to form a new star system with planets, asteroids, and comets. Note also the slightly brighter knot* at the base of the Horsehead that is likely a small young star already in formation. Also note the shadow cast by the base of the Horsehead slightly to its left. Stats for IC 434 are: RA: 05h 40m 40.0s, Dec: -02° 27' 00", no reference Magnitude, and size: 90.0'x14.0'.

*Hover over the image with a mouse for annotations.