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.
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