Photo Credit: David Malin at the Anglo-Australian Observatory; used with permission - please do not redistribute without permission!
Reflection nebulae are not glowing plasmas but are visible because
of light from nearby bright stars scattering off of dust particles.
The nearby star or stars are not hot enough to cause ionization in
the gas of the nebula but are bright enough to give sufficient
scattering to make the dust visible. Since wavelengths in the blue
are scattered more readily than red, reflection nebula tend to have
a blue shading. (This is the same scattering process that gives us
blue skies and red sunsets.) 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.
Page contributed by G. Samuel Lightner.
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