A spark thrown off the meeting of a star and a shield.
The colour overhead is not paint and not fire. It is a collision — ninety-three million miles in the making — that you happened to be standing under.
The sun is always exhaling. Roughly a million tonnes of charged particles leave it every second and ride outward on the solar wind, crossing the dark between us at some four hundred kilometres a second.
Earth meets them with a magnetic field — an invisible shield that bends the stream around the planet and funnels the strays down toward the poles, where the shield dips inward and finally touches the top of the air.
A hundred kilometres up, those particles strike oxygen and nitrogen. Each atom takes the blow, holds it for a fraction of a second, then hands the energy back as a single note of light.
Oxygen answers in green, and — higher, thinner, rarer — in deep red. Nitrogen fringes the falling curtains violet. Every ribbon is the visible edge of atoms relaxing, all at once, in the cold.
You wait for the cold to mean something. Tonight, at last, it does.