The Physics of the Aurora
The aurora is a space-weather light show. Charged particles streaming from the Sun get trapped by Earth's magnetic field, funneled toward the poles, and crash into the upper atmosphere — where each collision can release a photon.
Solar wind
The Sun constantly exhales plasma — mostly protons and electrons at ~400 km/s. Coronal mass ejections send denser bursts that trigger the brightest auroras a day or two later.
Magnetic funneling
Earth's magnetosphere deflects most solar wind, but field lines near the poles dive into the atmosphere. Charged particles spiral along these lines (Lorentz force) and rain down in oval zones around each magnetic pole — which is why auroras are polar.
Atomic excitation and color
Incoming particles excite oxygen and nitrogen. Oxygen emits the famous green (557.7 nm) around 100–300 km up and red above ~300 km; nitrogen adds blue and purple edges. The color is a direct fingerprint of the atom and altitude.
Why it shimmers
The rays and curtains trace magnetic field lines, and they dance because the incoming particle streams gust and shift — you're watching the magnetosphere breathe.
Try this yourself
- Check the Kp index forecast (0–9): Kp ≥ 5 can push auroras to mid-latitudes.
- Scatter iron filings around a bar magnet to see the field-line shape that guides the particles.