What spectral signature typically contributes a distinct blue-green glow to an emission nebula's palette?

Answer

Doubly ionized oxygen ($ ext{O}^{++}$)

The presence of doubly ionized oxygen ($ ext{O}^{++}$) is associated with spectral lines around 500.7 nm and 495.9 nm, which manifest as a blue-green emission.

What spectral signature typically contributes a distinct blue-green glow to an emission nebula's palette?

#Videos

What Makes Emission Nebulae Glow In Distinct Colors? - YouTube

What Makes Emission Nebulae Glow So Brightly? - Physics Frontier

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