NGC 6820 is an emission nebula that surrounds open cluster NGC 6823 in the constellation Vulpecula.
Emission nebulae are clouds of high temperature gas. The atoms in the cloud are energized by ultraviolet light from a nearby star and emit radiation as they fall back into lower energy states (in much the same way as a neon light). These nebulae are usually red because the predominant emission line of hydrogen happens to be red .
Velpecula is a faint constellation in the northern sky.
