The planetary K-index (Kp) is a global measure of geomagnetic activity on a 0–9 scale, updated every 3 hours by NOAA SWPC. Higher Kp means the sun has disturbed Earth's magnetic field — which drives aurora, degrades GPS accuracy, and causes HF radio blackouts.
Aurora chasers: if your latitude is above the row that matches the current Kp, aurora is visible directly overhead. Between rows and you may catch it on the poleward horizon.
Ham radio operators: Kp ≥ 5 degrades polar-crossing paths. Kp ≥ 7 shuts them entirely. Mid-latitude paths often remain workable.
Drone pilots and surveyors: RTK GPS begins drifting at Kp ≥ 5. At Kp ≥ 7 precision missions should be postponed — even ambulatory drone GPS at risk.
Satellite operators: radiation and drag both spike during high-Kp events. Coronaut's Operator lens covers this in detail.
NOAA publishes a new Kp value every 3 hours (00:00, 03:00, 06:00, etc UTC), computed from magnetometer stations worldwide. Coronaut polls their feed every 60 seconds so you see the latest published estimate as soon as it drops.
Kp is logarithmic (each step ≈ 2× activity); Ap is linear. Ap is the 24-hour average. Kp is what most public forecasts use because it's fresher.
NOAA Space Weather Prediction Center (SWPC). Coronaut streams the same feed the US Air Force and airline dispatchers use. It's US Government public domain — free for commercial use.
Yes — the live Kp value, dashboard, and browser alerts are free forever. Paid tiers add email delivery, push notifications, and vertical-specific tools (GPS accuracy for drones, HF band conditions for hams).