What Are Auroras?
Auroras (northern lights = aurora borealis, southern lights = aurora australis) are light displays in the upper atmosphere near Earth's magnetic poles. They occur when charged particles (mainly electrons and protons) from the solar wind or from coronal mass ejections (CMEs) enter the atmosphere along magnetic field lines and collide with oxygen and nitrogen atoms. The atoms are excited and then emit light when they return to lower energy states—green and red from oxygen, blue and purple from nitrogen. The result is the familiar curtains, arcs, and bands of the aurora.
From Sun to Atmosphere
The solar wind and CMEs carry charged particles toward Earth. Earth's magnetosphere deflects most of them, but when the interplanetary magnetic field couples with Earth's field (especially during geomagnetic storms), particles can enter along field lines toward the poles. They spiral into the upper atmosphere (roughly 80–300 km altitude) and collide with gas atoms. The stronger the geomagnetic storm (higher Kp index), the farther equatorward aurora can be seen.
When and Where
Aurora is most common at high latitudes (Arctic and Antarctic). At Kp 5–6 (storm conditions), it is often visible at mid-latitudes (e.g. northern US, central Europe). At Kp 7+, displays can reach lower latitudes. Dark, clear skies away from light pollution give the best view. Cosmic Radar shows an aurora outlook in the daily report based on the Kp index and space weather, so you can see when conditions are favorable.
Sources and further reading
- NOAA – Aurora forecast – 3-day aurora forecast
- AuroraWatch UK – Real-time aurora alerts and magnetometer data
- ESA Space Weather – European forecasts
- NASA – Aurora – Science of northern and southern lights