The Witch Head reflection nebula (IC2118), about 1000 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 dust which are simply reflecting the light of a nearby star or stars. The nearby star or stars are not hot enough to cause ionization in the gas of the nebula like in emission nebulae but are bright 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, in particular iron and nickel. The latter two are often aligned with the galactic magnetic field and cause the scattered light to be slightly polarized (Kaler, 1998). The distinction between these two types of nebulae was done by Edwin Hubble in 1922. Download high resolution version (750x987, 85 KB)This reflection nebula is associated with the bright star Rigel in the constellation Orion. ... Download high resolution version (750x987, 85 KB)This reflection nebula is associated with the bright star Rigel in the constellation Orion. ... The Witch Head Nebula (also known as IC 2118) is named after its shape, as can be seen seen on the right. ... A giant Hubble mosaic of the Crab Nebula, a supernova remnant. ... Interstellar cloud is the generic name given to an accumulation of gas, plasma and dust in our and other galaxies. ... This article is about the astronomical object. ... ... An emission nebula is a cloud of ionized gas ( a plasma) emitting light of various colors. ... In particle physics, scattering is a class of phenomena by which particles are deflected by collisions with other particles. ... Familiar concepts associated with a frequency are colors, musical notes, radio/TV channels, and even the regular rotation of the earth. ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... Edwin Hubble Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer, noted for his discovery of galaxies beyond the Milky Way and the cosmological redshift. ... Year 1922 (MCMXXII) was a common year starting on Sunday (link will display full calendar). ...

They 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). In particle physics, scattering is a class of phenomena by which particles are deflected by collisions with other particles. ... A typical daytime sky. ... A composite image showing the terminator dividing night from day, running across Europe and Africa. ...

Reflection nebulae and emission nebulae are often seen together and are sometimes both referred to as diffuse nebulae. An example of this is the Orion Nebula. In astronomy, diffuse nebulae is the common term for both reflection nebulae and emission nebulae. ... The entire Orion Nebula in visible light Optical images reveal clouds of gas and dust in the Orion Nebula; an infrared image (right) reveals the new stars shining within. ...

Some 500 reflection nebulae are known. Among the nicest of the reflection nebulae are those surrounding the stars of the Pleiades. A blue reflection nebula can also be seen in the same area of the sky as the Trifid Nebula. The giant star Antares, which is very red (spectral class M1), is surrounded by a large red reflection nebula. The Pleiades are an open cluster dominated by hot blue stars surrounded by reflection nebulosity A shorter exposure shows less nebulosity. ... The Trifid Nebula (also known as M20 and NGC 6514) is an H II region at right ascension 18h 02. ... Cross section of a red giant showing nucleosynthesis and elements formed According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ... This article or section does not cite its references or sources. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ...

Reflection nebulae are also usually sites of star formation. Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. ...

In 1922, Hubble published the result of his investigations on bright nebulae. One part of this work is the Hubble luminosity law for reflection nebulae which make a relationship between the angular size (R) of the nebula and the apparent magnitude (m) of the associated star: The Orion Nebula, a famous reflection nebula. ... Angular size is a measurement of how large or small something is using rotational measurement (degrees of arc, arc_minutes, and arc-seconds). ... // Headline text HEY!! HOW ARE YOU ALL?? Its nice of you to come read this page. ...

5 log(R) = -m + k

where k is a constant that depends on the sensitivity of the measurement. Logarithms to various bases: is to base e, is to base 10, and is to base 1. ...

References

• James B. Kaler (1998). Kosmische Wolken. Materie-Kreisläufe in der Milchstraße. Spektrum Akademischer Verlag.