What specific spectral line often results in the characteristic deep red glow seen in hydrogen-rich emission nebulae?

Answer

The $\text{H}\

For hydrogen, the most abundant element in emission nebulae, recombination often results in the characteristic deep red glow associated with the $\text{H}\alpha$ spectral line.

What specific spectral line often results in the characteristic deep red glow seen in hydrogen-rich emission nebulae?

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