Emission nebulae
Emission nebulae are clouds of gas that are excited to light by nearby young, hot stars. Such stars radiate much of the light in ultraviolet band. Such high energy photons cause ionization of the thin gas, and depending on molecular cloud composition, then emit lights of various wavelengths (colors). Most common element in emission nebulae is hydrogen.
Cygnus Wall HORGB Lagoon and Trifid wide field Elephant’s Trunk Ha Pacman inside IC1396 nebula in Cepheus – wide field image. NGC1499 California Pillars of creation in M16 Dark clouds in Cygnus Dark clouds in Cygnus Tadpoles in IC410 Bubble nebula and M52 Crescent nebula Cygnus centre Cygnus centre starless Veil nebula HORGB North America and Pelican Auriga centre Flaming Star Rosette nebula Heart nebula with Melotte 15 IC410 IC1805 Heart Tadpoles enlarged California NGC7822 in Cepheus NGC6914 area in Cygnus Pelican nebula Abell 21 IC417 Wizard nebula Sh2-155 Sh2-173 Pickering Triangle Sh2-132 Lion Sh2-112