The Rosette Nebula, NGC 2237, is a large cloud of glowing Hydrogen gas. It houses open star cluster NGC 2244, whose stars formed from the gas of the nebula and cause the nebula to emit the light we see. It is roughly 5000 light-years away in the constellation Monoceros.

120 minutes L and 120 minutes RGB (binned 2x2) on 2016-02-28 plus 240 minutes H-a (Astrodon 3 nm) on 2016-02-29 (blended with L and R) using a QSI 583 from northern New Jersey through an Astro-Physics 105mm refractor at f6.2. North is up. ©2016

This detail from the above image shows globules of dust and gas that appear dark against the glowing hydrogen.