Matt BenDaniel - Diffuse Nebulae Diffuse nebulae are vast clouds of gas that are gravitationally collapsing and forming stars. Massive stars radiate ultraviolet light, which causes hydrogen gas to fluoresce red.
Bluish nebulae contain dust grains that reflect the light of bright stars.
Magenta nebulae are both fluorescing and reflecting. Orange nebulae fluoresce the red light of hydrogen plus the teal light of oxygen. Click thumbnail image to see enlarged view and description.