DISCLAIMER: Science ahead!
I’m particularly excited to talk about this one. What are those ghost esque wavy streaks of green, blue, and orange that are often captured in astro photography? They’re not added with post process magic, you can see the subtle radiance with your naked eyes on a dark/ clear night, and it’s not even a rare occurrence!
During the day, ultraviolet light from the sun strips electrons off atoms and molecules in our atmosphere (Ionizing). After the sun sets, these electrons recombine with their host atoms and release energy that we observe as light of different colors! The brightest and most common color being green which stems from excited oxygen atoms beaming their photons directly into the yellow-green spectrum where our eyes are most sensitive.
Why does it streak across the sky?
Gravity (buoyancy) waves!
Imagine throwing a rock into a pond. Those resulting ripples are called gravity waves. The flat equilibrium between the water surface and air (both fluids) was disturbed by the rock and then buoyancy forces attempt to restore the equilibrium between the two. The water will return to its original height, overshoot, and then be pulled back down by gravity only to repeat the process until the energy is properly distributed.
Our entire atmosphere can be sectioned off into layers of various densities. I’m going to use the picture above as a reference. Lets imagine the water is our lower atmosphere and the air is our upper Thermosphere 60 miles above it. Wind rising above mountains, Jet Streams, even the pressure of thunderstorms can cause these exact same kind of waves between atmosphere layers. Wham, the already visible airglow in that upper Thermosphere begins to dance and form beautiful ribbons across the night sky. It's fun to track the stuff with your camera and watch it morph over time.
Our Earth Is Cool