Astronomy:Horsehead Nebula

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Short description: Dark nebula in the constellation Orion
Horsehead Nebula
Dark nebula
diffuse
Barnard 33.jpg
The Horsehead Nebula. The reflection nebula NGC 2023 is in the bottom left corner and the nebula itself near the centre, in the shape of the head of a horse. Photo taken in 2011
Observation data: J2000.0 epoch
Right ascension05h 40m 59.0s
Declination−02° 27′ 30.0"
Distance1,375±54[1][note 1] ly   (422±17[1] pc)
Apparent magnitude (V)6.8
Apparent dimensions (V)8 × 6 arcmins
ConstellationOrion
Physical characteristics
Radius3.5 ly
DesignationsBarnard 33, LDN 1630, IC 434
See also: Lists of nebulae

The Horsehead Nebula (also known as Barnard 33 or B33) is a small dark nebula in the constellation Orion.[2] 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.[3]

The Horsehead Nebula is approximately 422 parsecs or 1,375 light-years from Earth.[1][3] It is one of the most identifiable nebulae because of its resemblance to a horse's head.[4]

History

The nebula was discovered by Scottish astronomer Williamina Fleming in 1888 on a photographic plate taken at the Harvard College Observatory.[5][6] 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.[7]

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 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.[8] 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.[9] The darkness of the Horsehead is caused mostly by thick dust blocking the light of stars behind it.[10] The lower part of the Horsehead's neck casts a shadow to the left.[11] 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

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

  • Horsehead and Flame Nebulae, 384 mm scope, HaRGB, imaged with amateur equipment

  • The Horsehead Nebula in natural color

  • The Horsehead Nebula seen by SPECULOOS's Callisto telescope

  • Interstellar dust of the Horsehead Nebula as revealed by the Hubble Space Telescope

See also

  • List of Hubble anniversary images

Notes

  1. ↑ Based on the parallax of 2MASS J05405172-0226489, a young stellar object embedded in the 'head' of the nebula.

References

  1. ↑ 1.0 1.1 1.2 Brown, A. G. A. (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics 616: A1. doi:10.1051/0004-6361/201833051. Bibcode: 2018A&A...616A...1G. 
  2. ↑ Arnett, Bill (2000). "Horsehead Nebula". http://astro.nineplanets.org/twn/b33x.html. 
  3. ↑ 3.0 3.1 "VLT Images the Horsehead Nebula". 25 January 2002. https://www.eso.org/public/australia/news/eso0202/. 
  4. ↑ Sharp, Nigel (2014). "The Horsehead Nebula". Association of Universities for Research in Astronomy. http://www.noao.edu/image_gallery/html/im0057.html. 
  5. ↑ Alex Newman (28 August 2017). "Unearthing the legacy of Harvard's female 'computers'". https://www.bbc.co.uk/news/world-us-canada-40879870. 
  6. ↑ Cannon, Annie J. (June 1911). "Williamina Paton Fleming". Science 33 (861): 987–988. June 30, 1911. doi:10.1126/science.33.861.987. PMID 17799863. Bibcode: 1911Sci....33..987C. https://zenodo.org/record/1448062. 
  7. ↑ Barnard, E. E. (1919). "On the dark markings of the sky, with a catalogue of 182 such objects.". Astrophysical Journal 49: 1–24. doi:10.1086/142439. Bibcode: 1919ApJ....49....1B. 
  8. ↑ "The Horsehead Nebula/IC434". NOAO. https://noirlab.edu/public/images/noao0126a. 
  9. ↑ Morgan, W.W.; Lodén, Kerstin (1966). "Some Characteristics of the Orion Association". Vistas in Astronomy 8 (1): 83–88. doi:10.1016/0083-6656(66)90023-7. ISSN 0083-6656. Bibcode: 1966VA......8...83M. 
  10. ↑ Mayo Greenberg, J (2002). "Cosmic dust and our origins". Surface Science 500 (1–3): 793–822. doi:10.1016/S0039-6028(01)01555-2. ISSN 0039-6028. Bibcode: 2002SurSc.500..793M. 
  11. ↑ Nemiroff, R.; Bonnell, J., eds (21 July 2009). "The Horsehead Nebula". Astronomy Picture of the Day. NASA. https://apod.nasa.gov/apod/ap090721.html. 

External links



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