How PolarPeek works

The aurora verdict

For your place and tonight’s dark hours we combine four things:

1. Geomagnetic latitude. The aurora is organised around the geomagnetic pole, not the geographic one. We compute it with a tilted dipole (IGRF-14, pole at 80.8° N, 72.7° W).
2. Kp needed. From a linear fit to commonly reported viewing limits for 16 cities in Europe and North America we estimate the Kp at which the aurora shows low on the poleward horizon: Kp ≈ (66.75° − geomagnetic latitude) / 2.5. Seeing it overhead needs the oval about 4° closer. This is a rule of thumb accurate to roughly ±1 Kp; local horizon, light pollution and the storm’s shape matter.
3. Activity. NOAA SWPC’s observed and forecast 3-hour Kp, plus NOAA’s OVATION model probability for your grid cell (updated every few minutes).
4. Darkness and clouds. The Sun must be at least 12° below the horizon. Cloud cover comes from MET Norway’s global forecast, averaged over the dark hours.

The result is yes when the expected Kp clears your threshold with margin (or OVATION is high) and the sky is mostly clear; maybe when it is close or partly cloudy; unlikely otherwise. We never claim certainty: the aurora can surprise in both directions within an hour.

Nights per year

On place pages we count, for 2016–2025, the UT days whose maximum Kp reached the level needed there, from the GFZ Potsdam Kp archive. It is an upper bound: it ignores daylight, clouds and the Moon.

Moon, Sun, planets and eclipses

All positions, rise and set times, phases, eclipses, equinoxes and planetary events come from the open-source astronomy-engine library (MIT licence), which is accurate to better than an arcminute for this purpose. Meteor shower peaks are computed each year from the solar longitude in the International Meteor Organization’s working list. Supermoons are full Moons closer than 360,000 km.

ISS passes

We use NASA’s public ISS trajectory file (state vectors every four minutes for about two weeks), interpolate it, and compute passes higher than 10° for your location in your browser. A pass is marked visible when the station is sunlit while the Sun is at least 6° below your horizon. Orbit boosts can shift predictions by a few minutes until NASA publishes the next file.

What we do not do

We do not use paid data, do not resell anyone’s data and do not send your exact location to any server: weather requests are rounded to about 10 km.