Every number on the site comes from a public scientific source or from a calculation described here. The status is an estimate of viewing conditions, not a promise.
Data sources
- Kp index — NOAA Space Weather Prediction Center: observed and estimated 3-hour planetary K, the 3-day forecast and the 27-day outlook.
- Aurora oval — NOAA OVATION Prime: the probability of aurora on a 1° grid about 30 minutes ahead, driven by real-time solar wind.
- Solar wind — NOAA real-time solar wind from the spacecraft upstream of Earth: Bz, total field, speed and density.
- Clouds — Open-Meteo hourly cloud cover for each place.
- Darkness and moon — computed for each place and night: nautical and astronomical twilight, moon phase and illumination.
- Kp history — GFZ Potsdam definitive Kp since 2015 (CC BY 4.0), for aurora nights and storm days.
- Maps — outlines from Natural Earth (public domain), drawn by this site.
The Kp a place needs
The aurora oval is centered on the geomagnetic pole, so what matters is geomagnetic latitude, not geographic latitude. We compute each place's corrected geomagnetic latitude (AACGM-v2) at 110 km, the height of the aurora, and convert it into the Kp at which the oval's edge reaches that place's horizon for the naked eye. That is the "needs Kp" number on every page, to one decimal. The values drift slowly with Earth's magnetic field and are recomputed once a year.
On region pages we also show two more steps: about one Kp above the threshold the aurora is clearly visible, about two Kp above it climbs high into the sky. About one Kp below the threshold, a phone camera can still pick up a glow on the horizon.
Tonight's status
For each place and night, a score from 0 to 100 combines the expected Kp against the place's threshold, the OVATION probability nearby, cloud cover, darkness and moonlight. The site then caps the score twice. By Kp: when tonight's peak Kp is more than one below the threshold the score stays at 10 or less, and below the threshold it stays at 30 or less. A clear, moonless night cannot make up for activity that does not reach your latitude. By clouds: when the night's average cloud cover is 90% or more the score stays at 10 or less, and from 70% it stays at 54 or less. Strong activity cannot make up for an overcast sky. Kp is compared to one decimal, as it is printed: NOAA's Kp 5− (4.67) reaches a Kp 4.7 threshold.
| Score | Status |
|---|---|
| 0–14 | Unlikely |
| 15–34 | Low: faint, likely only on a camera |
| 35–54 | Moderate |
| 55–74 | High |
| 75–100 | Very high |
"Tonight" runs from 6 PM to 6 AM local time. The hourly table uses the same scale for each hour; hours before nautical dusk read "Too light". The best window is the two to four hours between 10 PM and 4 AM when the score is highest.
Aurora nights per year
A night counts when, between 6 PM and 6 AM local time, a 3-hour Kp block reached the place's threshold and the sun at local midnight was at least 12° below the horizon. The yearly figure is the average of the last three years; the monthly bars average every year since 2015. Clouds are not counted, so the number says how often space weather gave the place a chance, not how often someone saw the aurora.
Where to look
We give the compass direction from each place toward the geomagnetic pole (IGRF-14 for 2025): north to north-northeast across North America, north-northwest in Europe, south to south-southeast from Australia. Far from the oval the aurora sits low on that horizon; under the oval, look overhead too.
Updates and limits
- Kp and the solar wind update every few minutes, the oval about every five, clouds hourly. Pages refresh every few minutes; the time of the data is shown as "Updated … UTC".
- When a source is late, the page keeps the last valid numbers with their time stamp rather than showing an error.
- Kp forecasts beyond a day often miss the timing of storms by hours, and the 27-day outlook only repeats the Sun's rotation. Substorms can light up the sky for minutes while Kp stays modest.
- Local light pollution, haze, terrain and fog are not in the score. The dark-sky spots on each page are there to help with that.