An aurora is a natural light display at high latitudes, caused by charged solar particles colliding with atoms in Earth's upper atmosphere. The northern and southern lights are space weather made visible — their reach tracks geomagnetic activity, so strong storms push them toward the equator.
Understanding Aurora
How Auroras Form
The Sun continuously emits a stream of charged particles called the solar wind. When this plasma encounters Earth's magnetosphere, most of it is deflected — but some particles are captured and channelled along magnetic field lines toward the polar cusps. There, they spiral down into the upper atmosphere and collide with gas molecules, transferring energy. The excited molecules release this energy as visible light. During strong coronal mass ejections, the magnetosphere is compressed and disrupted, pushing the auroral oval equatorward and intensifying the display.
Colours and Altitude
| Colour | Element | Altitude | Notes |
|---|---|---|---|
| Green | Oxygen (O) | 100–300 km | Most common; dominant in moderate displays |
| Red | Oxygen (O) | 300–600 km | Seen in intense storms; high-altitude |
| Blue/Purple | Nitrogen (N₂) | 80–120 km | Edges and lower curtains |
| Pink | Nitrogen (N₂) | 100 km | Rare; lower fringe of intense auroras |
Aurora and Satellites
The same geomagnetic storms that produce spectacular auroras also pose risks to spacecraft. Enhanced atmospheric drag at LEO altitudes causes the upper atmosphere to expand, increasing drag on satellites and accelerating orbital decay. In February 2022, a geomagnetic storm caused the loss of 38 newly deployed Starlink satellites when increased drag pulled them back into the atmosphere before they could raise their orbits. Energetic particles associated with auroras can also cause single-event upsets in satellite electronics.