Reflection Nebula

Much like emission nebulae, reflection nebulae are full of gas and dust. However, the way they are oriented with stars means that they will look different.

NGC 1977: Blue Reflection Nebula in Orion
Credit: Anglo-Australian Telescope photograph by David Malin
Copyright: Anglo-Australian Telescope Board

Merope's Reflection Nebula
Image Credit & Copyright: Leonardo Orazi

Reflection nebulae do just what they name implies: they reflect light. When a star is off to the side of the nebula, as seen from Earth, the nebula will reflect the bluer light (i.e. the shorter wavelengths) towards Earth, and the nebula will appear bluish in color. The reason why the bluer light is reflected and not the redder light is the wavelengths. The gas and dust particles are small enough that the blue light will interact with them and be reflected while the redder light, on average, will just pass by the dust and gas.

How do we know that that reflected light is from the star? By looking at the spectra of the star and the nebula. A reflection nebula will have the same spectrum as the star that the light came from.


While the blue light is reflected, we know the red light passes through. This leads to another interesting phenomenon: reflection nebula can actual cause a star to appear redder than it really is. This is called stellar reddening.