What causes Emission Nebulae to characteristically glow red or pink?

Answer

Ionization and subsequent recombination of hydrogen atoms

Emission nebulae are energized by hot stars, causing the ionization of hydrogen; when the electrons recombine with the hydrogen nuclei, light is emitted, typically in the red portion of the spectrum.

What causes Emission Nebulae to characteristically glow red or pink?

#Videos

Nebulae: Crash Course Astronomy #36 - YouTube

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