Reflection nebula

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The Witch Head reflection nebula (IC2118), about 900 light years from earth, is associated with the bright star Rigel in the constellation Orion. The nebula glows primarily by light reflected from Rigel, located just outside the top right corner of the image. Fine dust in the nebula reflects the light. The blue color is caused not only by Rigel's blue color but because the dust grains reflect blue light more efficiently than red. Reflection.nebula.arp.750pix.jpg
The Witch Head reflection nebula (IC2118), about 900 light years from earth, is associated with the bright star Rigel in the constellation Orion. The nebula glows primarily by light reflected from Rigel, located just outside the top right corner of the image. Fine dust in the nebula reflects the light. The blue color is caused not only by Rigel's blue color but because the dust grains reflect blue light more efficiently than red.

In astronomy, reflection nebulae are clouds of interstellar dust which might reflect the light of a nearby star or stars. The energy from the nearby stars is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust visible. Thus, the frequency spectrum shown by reflection nebulae is similar to that of the illuminating stars. Among the microscopic particles responsible for the scattering are carbon compounds (e. g. diamond dust) and compounds of other elements such as iron and nickel. The latter two are often aligned with the galactic magnetic field and cause the scattered light to be slightly polarized. [1]



Reflection nebula IC 2631. Young star lights up reflection nebula IC 2631.jpg
Reflection nebula IC 2631.
Reflection Nebula vdB1 VdB1.jpg
Reflection Nebula vdB1

Analyzing the spectrum of the nebula associated with the star Merope in the Pleiades, Vesto Slipher concluded in 1912 that the source of its light is most likely the star itself, and that the nebula reflects light from the star (and that of the star Alcyone). [3] Calculations by Ejnar Hertzsprung in 1913 lend credence to that hypothesis. [4] Edwin Hubble further distinguished between the emission and reflection nebulae in 1922. [5]

Reflection nebulae are usually blue because the scattering is more efficient for blue light than red (this is the same scattering process that gives us blue skies and red sunsets).

Reflection nebulae and emission nebulae are often seen together and are sometimes both referred to as diffuse nebulae.

Some 500 reflection nebulae are known. A blue reflection nebula can also be seen in the same area of the sky as the Trifid Nebula. The supergiant star Antares, which is very red (spectral class M1), is surrounded by a large, red reflection nebula.

Reflection nebulae may also be the site of star formation.

Luminosity law

Cosmic dust clouds in Messier 78. Cosmic dust clouds in reflection nebula Messier 78.jpg
Cosmic dust clouds in Messier 78.

In 1922, Edwin Hubble published the result of his investigations on bright nebulae. One part of this work is the Hubble luminosity law for reflection nebulae, which makes a relationship between the angular size (R) of the nebula and the apparent magnitude (m) of the associated star:

5 log(R) = -m + k

where k is a constant that depends on the sensitivity of the measurement.

See also

Related Research Articles

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A protoplanetary nebula or preplanetary nebula is an astronomical object which is at the short-lived episode during a star's rapid evolution between the late asymptotic giant branch (LAGB) phase and the subsequent planetary nebula (PN) phase. A PPN emits strongly in infrared radiation, and is a kind of reflection nebula. It is the second-from-the-last high-luminosity evolution phase in the life cycle of intermediate-mass stars.

IC 349 Nebula in the constellation of Taurus

IC 349, also known as Barnard's Merope Nebula, is a nebula which lies 3500 AUs from the star Merope in the Pleiades cluster.

WR 31a Wolf Rayet star in the constellation Carina

WR 31a, commonly referred to as Hen 3-519, is a Wolf–Rayet (WR) star in the southern constellation of Carina that is surrounded by an expanding Wolf–Rayet nebula. It is not a classical old stripped-envelope WR star, but a young massive star which still has some hydrogen left in its atmosphere.


  1. Kaler, 1997.
  2. "A Star's Moment in the Spotlight" . Retrieved 10 February 2016.
  3. Slipher, Vesto M. (1922). "On the spectrum of the nebula in the Pleiades". Lowell Observatory Bulletin. 2: 26–27. Bibcode:1912LowOB...2...26S.
  4. Hertzsprung, E. (1913). "Über die Helligkeit der Plejadennebel". Astronomische Nachrichten. 195 (23): 449–452. Bibcode:1913AN....195..449H. doi:10.1002/asna.19131952302.
  5. Hubble, E. P. (1922). "The source of luminosity in galactic nebulae". Astrophysical Journal. 56: 400. Bibcode:1922ApJ....56..400H. doi:10.1086/142713.
  6. "Sifting through Dust near Orion's Belt". ESO Press Release. Retrieved 2 May 2012.