Horsehead Nebula

Horsehead Nebula

Nebula
diffuse
The Horsehead Nebula. The reflection nebula NGC 2023 is in the bottom left corner and the nebula itself near the center, in the shape of the head of a horse. Photo taken in 2011
Observation data: J2000.0 epoch
Right ascension	05h 40m 59.0s
Declination	−02° 27′ 30.0"
Distance	1,375±54 ly   (422±17 pc)
Apparent dimensions (V)	8 × 6 arcmins
Constellation	Orion
Physical characteristics
Radius	3.5 ly
Designations	Barnard 33, LDN 1630, IC 434

The Horsehead Nebula (also known as Barnard 33) is a small dark nebula in the constellation Orion. The nebula is located just to the south of Alnitak, the easternmost star of Orion's Belt, and is part of the much larger Orion Molecular Cloud Complex. It appears within the southern region of the dense dust cloud known as Lynds 1630, along the edge of the much larger, active star-forming H II region called IC 434. The Horsehead Nebula is approximately 422 parsecs or 1,375 light-years from Earth. It is one of the most identifiable nebulae because of its resemblance to a horse's head.

History

The nebula was first recorded in 1888 by British astronomer Williamina Fleming on a photographic plate taken at the Harvard College Observatory. One of the first descriptions was made by E. E. Barnard, describing it as: "Dark mass, diam. 4′, on nebulous strip extending south from ζ Orionis", cataloguing the dark nebula as Barnard 33.

Structure

Orion's Belt with Alnitak on the left-hand side and the Horsehead Nebula directly below it.

The dark cloud of dust and gas is a region in the Orion Molecular Cloud Complex where star formation is taking place. It is located in the constellation of Orion, which is prominent in the winter evening sky in the Northern Hemisphere and the summer evening sky in the Southern Hemisphere.

Colour images reveal a deep-red colour that originates from ionised hydrogen gas (Hα) predominantly behind the nebula, and caused by the nearby bright star Sigma Orionis. Magnetic fields channel the gases, shaping the nebula into streams, shown as foreground streaks against the background glow. A glowing strip of hydrogen gas marks the edge of the enormous cloud, and the densities of nearby stars are noticeably different on either side.

Heavy concentrations of dust in the Horsehead Nebula region and neighbouring Orion Nebula are localized into interstellar clouds, resulting in alternating sections of nearly complete opacity and transparency. The darkness of the Horsehead is caused mostly by thick dust blocking the light of stars behind it. The lower part of the Horsehead's neck casts a shadow to the left. The visible dark nebula emerging from the gaseous complex is an active site of the formation of "low-mass" stars. Bright spots in the Horsehead Nebula's base are young stars in the early process of forming.

• 

  Hubble Space Telescope infrared image.

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  Seen through a regular telescope, with a regular camera.

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  From the European Southern Observatory, 2002

See also

• Horsehead Nebula in fiction

External links

• The Horsehead Nebula @ The Electronic Sky
• Hubble Observes the Horsehead Nebula
• The discovery of early photographs of the Horsehead nebula, by Waldee and Hazen
• The Horsehead Nebula in the 19th Century, by Waldee
• Detection of new nebulae by photography, by Pickering
• Horsehead Nebula at ESA/Hubble
• The Horsehead Nebula at the Astro-Photography site of Mr. T. Yoshida.
• The Horsehead-Nebula and neighboring structures in a classical view
• The Horsehead Nebula on interactive astro-photography survey at Wikisky.org
• The Horsehead Nebula at Constellation Guide