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Deep Field
29 September 2026 2518 stories tracked

Glossary · The Sun & Space Weather

The G, R and S scales

Three separate one-to-five scales for the three separate ways the Sun causes trouble.

NOAA grades geomagnetic storms G1 to G5, radio blackouts R1 to R5 and solar radiation storms S1 to S5. They are independent: a flare produces a radio blackout within minutes, a particle storm within an hour, and a geomagnetic storm only if a coronal mass ejection follows and is aimed correctly, a day or two later. Conflating them is the most common error in coverage — a big flare does not necessarily mean aurora, and a big aurora does not necessarily follow a big flare.

Related terms

Coronal mass ejection A billion tonnes of solar atmosphere thrown into space, and the cause of most serious aurorae. Solar flare classes A, B, C, M, X — a logarithmic scale for how hard the Sun just flashed in X-rays. Kp index A 0–9 scale of how disturbed Earth's magnetic field is right now. The solar cycle An eleven-year rhythm in sunspots, flares and the Sun's entire magnetic field.

Questions

What is G, R and S scales?

Three separate one-to-five scales for the three separate ways the Sun causes trouble.

Why does it matter?

They are independent: a flare produces a radio blackout within minutes, a particle storm within an hour, and a geomagnetic storm only if a coronal mass ejection follows and is aimed correctly, a day or two later. Conflating them is the most common error in coverage — a big flare does not necessarily mean aurora, and a big aurora does not necessarily follow a big flare.

Written and computed by . Corrections and errors to hello@cantinalabs.dev.