AuroraCast — glossary

Name: AuroraCast live feed
Creator: AuroraCast

Plain-language definitions of the terms used across AuroraCast (NOAA SWPC + GFZ).

The aurora

Aurora borealis / australis: The aurora seen near the north (borealis) and south (australis) magnetic poles. The two form near-mirror ovals that brighten and expand together during storms.
Auroral oval: The ring-shaped zone, centered on each magnetic pole, where the aurora is most likely. It widens toward the equator as geomagnetic activity (Kp) rises.
Magnetosphere: The region around Earth shaped by its magnetic field. It deflects most of the solar wind but funnels some charged particles toward the poles, creating the aurora.
Emission color: The aurora’s color, set by which gas is excited and at what altitude: oxygen glows green (around 557 nm) and red, while nitrogen adds blue and purple.

Kp index: A 0–9 planetary scale of geomagnetic activity over a three-hour window, derived from ground magnetometers. Higher Kp pushes the auroral oval to lower latitudes; Kp 5+ is a storm.
G-scale (G1–G5): NOAA’s geomagnetic storm scale, mapped from Kp: Kp 5 = G1 (minor) through Kp 9 = G5 (extreme). It also flags storm impacts on power grids, satellites and radio.
Geomagnetic storm: A major disturbance of Earth’s magnetic field (Kp ≥ 5) driven by enhanced solar wind, usually after a coronal mass ejection — the events that bring the aurora to lower latitudes.
OVATION model: NOAA SWPC’s aurora model that estimates the location and intensity of the auroral oval, used to map where the lights are likely to be visible right now.

Solar wind: The continuous stream of charged particles flowing from the Sun. Faster, denser, southward-pointing solar wind couples more strongly to Earth and brightens the aurora.
Coronal mass ejection (CME): A large cloud of magnetized plasma launched from the Sun. An Earth-directed CME arrives in one to three days and can trigger a geomagnetic storm and far-reaching aurora.
Solar flare: A sudden burst of radiation from the Sun’s surface, often near sunspots and frequently paired with a CME. Flares signal that a magnetically active region may drive aurora.
Solar cycle: The roughly 11-year rise and fall of solar activity. Near solar maximum, sunspots, flares and CMEs peak, so storms and far-reaching auroras become more frequent.