Nebula by reflection
In Astronomy, the Nébuleuse S by reflection are clouds of dust which reflects simply the Lumière of one or more star S neighbors. These stars are not enough hot to cause the ionization of the Gaz, like in the case of the nebulas in emission, but are enough luminous to allow a sufficient dispersion to make dust visible. The distinction between these two types of nebulas was made by Edwin Hubble in 1922.
Nebulas by reflection are usually blue because dispersion is more effective for the blue light than it red (it is the same process of dispersion which gives us the blue skies and of the red sunsets).
Nebulas by reflection and the nebulas in emission are often seen together, such as for example the Nébuleuse of Orion and are sometimes gathered in only one type: the diffuse nebulas .
Approximately 500 nebulas per reflection are known. Among most beautiful nebulas of reflection have finds the entourage of stars of the Pléiades. A nebula by blue reflection can also be seen in the same sector of the sky as the Nébuleuse Trifide. The giant star Antarès, which is very red (spectral class M1), is surrounded by a great nebula of red reflection.
Nebulas by reflection are often sites of formation of stars.
In 1922, Edwin Hubble published the result of its investigations on nebula luminous. Part of this work is the law of luminosity of Hubble for nebulas of reflection which established a relation between the angular size ( R ) of nebula and the Magnitude connect ( m ) of associated star:
- 5 log ( R ) = - m + K
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