AuroraCast

The aurora — the northern lights (aurora borealis) and their southern twin (aurora australis) — is light given off when charged particles from the Sun, funneled by Earth’s magnetic field, slam into gases high in the atmosphere. Most of the glow happens between about 100 and 300 km up, where oxygen lights up green (around 557 nm) and red, and nitrogen adds blue and purple fringes.

AuroraCast turns NOAA SWPC space-weather data into a plain answer to one question: how likely are the lights tonight, and how far south might they reach? The key number is the Kp index — a 0–9 scale of global geomagnetic activity. The higher the Kp, the lower the latitude where the aurora becomes visible, so a quiet Kp 2 stays near the poles while a storm-level Kp 7 can bring the lights to mid-latitudes.