Astronomy Encyclopedia

Space Weather & Observatory Navigator

Real-time Kp index, geomagnetic storm alerts, and curated links to national observatories — all in your browser.

Space Weather Live

Source: NOAA SWPC · Cached up to 15 minutes

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National Observatory Directory

Curated links to the world's leading space agencies, telescope networks, and amateur astronomy resources

Ground Observatories

Space Weather Explained

What Is the Kp Index?

The planetary K-index (Kp) measures global geomagnetic activity on a 0–9 scale, averaged over 13 ground stations. Values above 5 indicate storm conditions. A Kp of 7+ brings aurora to mid-latitudes.

Geomagnetic Storm Scales

NOAA classifies storms G1–G5. G1 causes minor power grid fluctuations; G5 can cause widespread HF radio blackouts and satellite drag anomalies. G3+ storms are visible on news headlines.

When & Where to See Aurora

Kp ≥ 5 brings northern lights to ~60°N; Kp ≥ 7 to ~50°N; Kp = 9 to ~40°N. Look during the darkest hours after astronomical twilight in a clear northern sky far from city lights.

Solar Cycle 25

Solar Cycle 25 peaked around 2025 with historically high sunspot counts. More spots mean higher Kp storm frequency, stronger radio blackouts, and more aurora events for observers at mid-latitudes.

Frequently Asked Questions