A strange flickering light

The Valkyrior are warlike virgins, mounted upon horses and armed with helmets and spears. [...] When they ride forth on their errand, their armour sheds a strange flickering light, which flashes up over the northern skies, making what men call the "aurora borealis", or "Northern Lights".

("Bulfinch's Mythology", by Thomas Bulfinch, 1855)

Polar Auroras, also known as northern and southern (polar) lights, are natural light displays in the sky, particularly in the polar regions, and usually observed at night.
Typically the aurora appears either as a diffuse glow or as "curtains" that approximately extend in the east-west direction. At some times, they form "quiet arcs"; at others ("active aurora"), they evolve and change constantly.

If the sun rises at midnight

Norway, midnight sun (montage)

The North Pole and the South Pole are two geographic places described by the opposite alternance of light and dark.

At the North Pole, the sun is permanently above the horizon during the summer months (March-September) and permanently below the horizon during the winter months (September-March).
At the South Pole it's just the contrary: during the southern winter (March–September), the South Pole receives no sunlight at all, but in the summer (September–March), the sun is continuously above the horizon.

The midnight sun is a natural phenomenon occurring in summer months at latitudes north and nearby to the south of the Arctic Circle, and south and nearby to the north of the Antarctic Circle where the sun remains visible at the local midnight. The opposite phenomenon, polar night, occurs in winter when the sun stays below the horizon throughout the day.