Reflection nebula
A cloud of dust that shines by reflecting the light of nearby stars, usually bluish.
Dust grains scatter blue light more than red — the same reason the daytime sky is blue — so reflection nebulae look blue in photographs. They don't produce light of their own, so nebula filters don't help; they only dim them.
The Pleiades are wrapped in faint reflection nebulosity (the Merope Nebula is the brightest part); M 78 in Orion is the brightest reflection nebula in the Messier catalog.
At the eyepiece
Clean optics and a dark, transparent sky matter: dew or dust on a lens scatters light and can mimic nebulosity around bright stars.
Examples in the sky
- M 78 (NGC 2068)
- Merope Nebula (NGC 1435)
- Witch Head Nebula (NGC 1909)
- Hubble's Variable Nebula (NGC 2261)