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Corey S Powell's posts Post Back to profile
Corey S Powell

So many beautiful aurora photos going around right now. Wonder where those amazing colors come from? Here's a helpful breakdown.

When you split up the light of a typical aurora, it looks like this.

Many colors from just nitrogen & oxygen!

swpc.noaa.gov/content/aurora-t #aurora #space #science #nature

Different auroral colors come from different heights in the atmosphere primarily because the life-time of an excited atom or molecule (time spent in its excited state) is vastly different for different colors of the aurora. The green aurora from oxygen in the 1S state typically occurs from 120 to 400 km (80 to 250 miles) above the surface of Earth. The red aurora from oxygen in the 1D state is restricted to altitudes above 300 km (180 km). This is because oxygen in the 1D state has a very long lifetime (>150 sec) and can only survive in the thinner atmosphere above 300 km. At lower altitudes the oxygen in the 1D state collides with other atmospheric atoms or molecules before it can emit a photon which deactivates or quenches the excited oxygen. The 1S state of oxygen has a lifetime of about 1 second and therefore emits a photon more quickly and thus can emit at lower altitudes where the density is higher. The aurora sometimes has a purplish lower border which comes from emissions from molecular nitrogen. This "prompt" emission is emitted from excited states of nitrogen that have almost no delay between excitation and emission. It survives at even lower altitudes between 120 and 200 km (80 to 120 miles).
12 May at 7:08 | Open on mastodon.social
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Corey S Powell

Colors of an aurora depend not only on which element is emitting light, but also on *where* it is.

Oxygen at high altitudes glows red; at lower altitudes it glows green. Purple nitrogen is lower still.

Atoms are complicated creatures!

#aurora #science #nature #physics

Graphical breakdown of the colors of an aurora, and how they arise in different layers of the atmosphere.
12 May at 7:10 | Open on mastodon.social
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