The sky keeps a record of the sun.
Every curtain of light is a message that left the sun days ago and finished its journey forty miles above your head. Scroll to follow one down.
It begins with the sun losing its temper.
A coronal mass ejection throws a billion tons of charged gas off the sun's surface in a matter of minutes. It leaves at close to two million miles an hour, and it does not slow down for anyone.
From that moment the light over your head is already on its way. It just has an ocean of empty space to cross first.
Three days of nothing, then a wall.
The cloud crosses the solar system and meets the magnetosphere, the magnetic shell the Earth's molten core spins into being. Most of the storm slides around us and carries on into the dark.
Some of it does not. Where the field lines dip toward the poles, the storm finds a way in.
Color is just altitude and chemistry.
The particles funnel down the field lines and slam into the upper atmosphere at a hundred miles up. What they strike, and how high they strike it, decides the color you see.
And then it just hangs there, moving like weather.
The light gathers into folded sheets and rippling rays, driven by the same magnetic tension that let it in. It can fill the whole sky or vanish in a breath. The only way to know is to be outside, looking up, when it decides to appear.
Tonight's activity is worth the cold.
A Kp of six pushes the auroral oval down over the horizon of the northern states. Get away from town lights, give your eyes twenty minutes to adjust, and look north.
Go outside.
Ninety-three million miles of weather, and it ends as light you can only see by standing in the dark.
Back to the surface of the sun