What is the Kp index?
The Kp index is a number from 0 to 9 that measures how disturbed Earth's global magnetic field is over a three-hour window — 0 is dead calm, 5 marks the start of a geomagnetic storm, and 9 is an extreme storm. The higher the Kp, the stronger the aurora and the further from the poles it can be seen.
What Kp actually measures
Kp (the 'planetary K-index') is averaged from magnetometers at stations around the world, which record how much the solar wind is rattling Earth's magnetic field. Each whole step up represents a roughly doubling of disturbance, and pushes the auroral oval about 2° of latitude toward the equator — which is why a higher number literally means the northern lights slide further south.
Kp and the G-storm scale
NOAA maps the top of the scale onto storm classes: Kp 5 = G1 (minor), Kp 6 = G2 (moderate), Kp 7 = G3 (strong), Kp 8 = G4 (severe), Kp 9 = G5 (extreme). Below Kp 5 the field is 'quiet' to 'active' with no storm class. A G5 can dim power grids and scramble GPS; for aurora-watchers it means a once-in-years show visible far into the mid-latitudes.
See the live number
Cosmik reads the live Kp from NOAA and turns it into a plain-English verdict. See the current value and the full 0–9 storm table on live solar activity, the definition in the Kp index glossary entry, or tonight's visibility for your city on the aurora forecast.
Keep exploring
- Live Kp index & the 0–9 storm scale
- Kp index — glossary definition
- Tonight's aurora forecast for your city
- All space explainers
See it yourself tonight
Theory is better with a sky. Get the next ISS pass times over New York, London, Paris, Tokyo, Berlin or Sydney — or any of 550+ cities. Aurora hunter? Check tonight's forecast for your city.
