Aurora Kp Index

The Kp index (Planetarische Kennziffer, or planetary K-index) is the gold standard metric for measuring geomagnetic storm activity and predicting aurora visibility worldwide. Developed in 1949 by Julius Bartels, this logarithmic scale runs from 0 (quiet magnetic conditions) to 9 (severe geomagnetic storm), with each integer step representing approximately a doubling of geomagnetic activity. The Kp index is derived from measurements at 13 mid-latitude magnetic observatories distributed globally, providing a comprehensive snapshot of planetary-scale magnetic disturbances caused by solar wind interactions with Earth's magnetosphere.

For aurora photographers, the Kp index serves as the primary planning tool: Kp 0-2 indicates minimal aurora activity visible only at polar latitudes, Kp 3-4 brings auroras to typical northern viewing locations like Alaska and northern Scandinavia, Kp 5-6 extends visibility to southern Canada and northern Europe, while Kp 7-9 during major geomagnetic storms can push spectacular auroral displays as far south as the northern United States or central Europe.

PhotoWeather integrates NOAA's 3-day Kp forecast from the Space Weather Prediction Center, providing hourly predictions that help photographers plan multi-day aurora expeditions. Understanding Kp values is essential for maximizing your chances of witnessing and capturing the northern or southern lights: combine high Kp predictions with clear skies, minimal light pollution, and proper camera settings for stunning aurora photography.