Can you see the northern lights in Oulu tonight?
This page answers that from four things: how dark the sky gets, how much cloud
there is, where the moon is, and live magnetic activity measured at the Finnish
Meteorological Institute's nearest magnetometer, about 100 km away.
It needs JavaScript, because the positions of the sun and moon are calculated in
your browser rather than on a server — which is also why the darkness reading keeps
working when the network does not.
Aurora season in Oulu runs roughly from September to April. Between late April
and mid‑August the sky never gets dark enough, whatever the sun is doing.