Geomagnetic storm
A geomagnetic storm is a temporary disturbance of Earth's magnetic field driven by bursts of solar wind and coronal mass ejections from the Sun.
Storms are ranked from G1 (minor) to G5 (extreme) and correspond to a Kp of 5 or more, expanding the aurora and sometimes disrupting radio, GPS and power grids.
The strongest storms can make the northern lights visible far from the poles, occasionally into the mid-latitudes.
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Related terms
- Kp index — The Kp index is a 0–9 scale of global geomagnetic activity over three-hour periods, and it is the number aurora watchers check to judge tonight's odds.
- Twilight — Twilight is the period before sunrise and after sunset when the sky is partly lit by the Sun below the horizon, split into civil, nautical and astronomical stages.
