An interstellar cloud of gas and dust that shines because light from nearby bright stars is reflected or scattered toward the observer by cosmic dust particles contained in the cloud. The nebula's spectrum contains absorption lines characteristic of the spectrum of nearby illuminating stars. The emission component of its spectrum is due to gas; the reflection component, to dust. Reflection nebulae often appear bluish because blue light is more efficiently reflected by dust particles than red light. A familiar example is the nebulosity seen around some of the stars in the Pleiades, for example the Merope Nebula.
