Aurora & space-weather glossary

Aurora (borealis / australis)

The glow from solar particles exciting gases high in the atmosphere — green from oxygen at ~100–250 km, red higher up, purples from nitrogen.

Kp index

A 0–9 planetary measure of geomagnetic disturbance over 3-hour blocks. Higher = the auroral oval reaches lower latitudes.

Bz

The north–south part of the solar wind's magnetic field. Southward (negative) Bz drives aurora.

CME (coronal mass ejection)

A blast of solar plasma and magnetic field. A CME hitting Earth can trigger a geomagnetic storm a day or more after the flare.

G-scale (G1–G5)

NOAA's geomagnetic storm scale, from minor (G1, Kp 5) to extreme (G5, Kp 9).

Substorm

A sudden brightening and dancing of the aurora as the magnetosphere releases stored energy — the 'show' inside a storm.

OVATION

NOAA's model of aurora probability across the globe, updated frequently, forecasting ~30 minutes ahead.

Solar wind

The stream of charged particles flowing from the Sun, carrying its magnetic field past Earth.

L1 (Lagrange point 1)

A spot ~1.5 million km sunward where spacecraft sample the solar wind before it reaches Earth — our early-warning post.

Geomagnetic latitude

Latitude measured from the geomagnetic pole rather than the geographic one — what actually governs where aurora appears.

Hemispheric power

The total energy (in gigawatts) flowing into one hemisphere's aurora, from the OVATION model.