1 · Kp index (NOAA SWPC)
The planetary geomagnetic index, 0–9. Your location's magnetic latitude decides the threshold: London needs Kp 7, Tromsø only needs Kp 3.
Tonight · — · your location
Detecting your location…
MAYBE
Kp 5 is high enough for you, but clouds and 78% moon will cut visibility in the late evening. Best window 23:00–02:00 local.
7
Kp
weight 35%
3
Cloud
weight 25%
4
Moon
weight 15%
9
Darkness
weight 15%
8
Pollution
weight 10%
Tue
23
GO
Wed
24
MAYBE
Thu
25
NO
Fri
26
LOW
Sat
27
MAYBE
Sun
28
GO
Mon
29
GO
View the 7-night outlook for your city
City-specific Kp forecast, cloud cover graph, and the best night of the week.
How we decide a quick tour of the 5 factors
2 · Cloud cover (Open-Meteo)
Hourly total cloud at your coordinates. Below ~30% is fine; above 80% usually blocks the show.
3 · Moon phase & illumination
Above 70% illumination washes out all but the strongest Kp. Below 30% is essentially "extra dark".
4 · Darkness window
Astronomical twilight ends when the sun is 18° below the horizon. Earlier sunset ≠ earlier aurora.
5 · Light pollution (Bortle)
From our pre-computed Bortle grid. Class 4–9 cities need stronger Kp to see anything.
Quick answers
How accurate is this aurora forecast?
Short-term (under 3 hours) is the most accurate. The 27-day outlook from NOAA is research-grade — useful for planning, not for promising a show.
What does MAYBE mean?
Part of the night will work but a single factor (cloud, moon, twilight) is hurting. Open the breakdown to see which.
Do I need to sign up?
No. No signup, no app install, no account, no cookies, no email collection.
Why is my city wrong?
We use a public IP geolocation service. If you share a corporate VPN or mobile carrier, the result can be off. Use the city picker (coming soon) to override.
The northern lights, explained simply
The aurora borealis — and its southern twin, aurora australis — appears when charged particles from the Sun (the solar wind) collide with gases in Earth's upper atmosphere. The colour depends on which gas is hit and at what altitude: green from oxygen around 100–300 km, red from oxygen above 200 km, blue and purple from nitrogen lower down.
What you actually see depends on three things: how strong the solar wind is when it hits Earth's magnetic field, how dark your sky is, and whether clouds get in the way. We track all three in real time and combine them into the single answer above.
The 27-day cycle
The Sun rotates on its axis every ~27 days. Active regions (sunspots, coronal holes) often persist across one or two rotations — that's why NOAA publishes a 27-day outlook. Use it to spot windows of opportunity, not promises.
Solar maximum (2024–2026)
We are inside the most active period of the current ~11-year solar cycle. More sunspots means more frequent and more intense geomagnetic storms. Autumn 2026 is statistically the best viewing window for the next 12 months.