The days will now get longer and longer fast. The midnight sun is set to reach Abisko and Karesuando on May 25th, followed by the city of Kiruna on May 28th. It will reach the Arctic Circle just before Midsummer’s Eve and then the days will get darker again.
Midnight sun, as well as polar night, the period of the year where the sun does not rise above the Arctic Circle, are both caused by the axial tilt of the Earth and its revolution around the sun.
In the northern hemisphere the North Pole is tilted towards the sun in summer, so instead of setting, the sun instead moves in a horizontal circle above the horizon. From midsummer, the North Pole gradually turns away from the sun, with the nights getting darker and darker until midwinter.
The same is true in the southern hemisphere, with a six-month time difference – that’s why summer and winter occur at different times in both hemispheres.