The Horsehead Nebula (also known as Barnard 33) is a small

dark nebula A dark nebula or absorption nebula is a type of interstellar cloud, particularly molecular clouds, that is so dense that it obscures the visible wavelengths of light from objects behind it, such as background stars and emission or reflection nebu ...

in the constellation Orion. The nebula is located just to the south of

Alnitak Alnitak is a triple star system in the constellation of Orion. It has the designations ζ Orionis, which is Latinised to Zeta Orionis and abbreviated Zeta Ori or ζ Ori, and 50 Orionis, abbreviated 50 Ori. The system is located at a ...

, the easternmost star of

Orion's Belt Orion's Belt or the Belt of Orion, also known as the Three Kings or Three Sisters, is an asterism in the constellation Orion. It consists of the three bright stars Alnitak, Alnilam and Mintaka. Looking for Orion's Belt is the easiest way to ...

, and is part of the much larger

Orion molecular cloud complex The Orion molecular cloud complex (or, simply, the Orion complex) is a star-forming region with stellar ages ranging up to 12 Myr. Two giant molecular clouds are a part of it, Orion A and Orion B. The stars currently forming within the complex a ...

. 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 An H II region or HII region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds ...

called

IC 434 IC 434 is a bright emission nebula in the constellation Orion. It was discovered on February 1, 1786 by William Herschel. The Horsehead Nebula is a dark nebula silhouetted against it. See also * Orion molecular cloud complex The Orion mole ...

. 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 Scottish astronomer Williamina Fleming on a photographic plate taken at the

Harvard College Harvard College is the undergraduate college of Harvard University, an Ivy League research university in Cambridge, Massachusetts. Founded in 1636, Harvard College is the original school of Harvard University, the oldest institution of higher lea ...

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 In library and information science, cataloging ( US) or cataloguing ( UK) is the process of creating metadata representing information resources, such as books, sound recordings, moving images, etc. Cataloging provides information such as auth ...

the dark nebula as Barnard 33.

Structure

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 Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

gas ( Hα) predominantly behind the nebula, and caused by the nearby bright star Sigma Orionis. Magnetic fields channel the gases, leaving 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 Dust is made of fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian process), volcanic eruptions, and pollution. Dust in ho ...

in the Horsehead Nebula region and neighbouring Orion Nebula are localized into

interstellar cloud An interstellar cloud is generally an accumulation of gas, plasma, and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium, the matter and radiation that exists in ...

s, 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 just in the process of forming.

Image gallery

Image:Orion Belt.jpg,

with

on the left-hand side and the Horsehead Nebula directly below it File:Horsehead and flame Nebulea 384mm scope Ha-RGB.jpg, Horsehead and Flame Nebulae, 384 mm scope, HaRGB, imaged with amateur equipment File:Horsehead nebula.png, The Horsehead Nebula in natural color File:Nebulosa testa di cavallo con SPECULOOS.jpg, The Horsehead Nebula seen by SPECULOOS's Callisto telescope File:Horsehead-Hubble.jpg, Interstellar dust of the Horsehead Nebula as revealed by the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

Notes

References

External links

SOFIA/upGREAT [C II] Velocity Resolved Map of the Horsehead Nebula

Hubble Observes the Horsehead Nebula

The discovery of early photographs of the Horsehead nebula, by Waldee and Hazen

Detection of new nebulae by photography, by Pickering

Horsehead Nebula at ESA/Hubble

* ttp://commons.wikimedia.org/wiki/File:HorseheadHunterWilson.jpg 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
{{Authority control Orion (constellation) Dark nebulae Barnard 33 Star formation Barnard objects