Polar night
The polar night is when it stays dark outside for more than twenty four hours. This occurs only inside the polar circles (the northernmost and southernmost areas on Earth).[1] A lot of times It will be a polar night for the winter and the opposite happens in the summer.

Early afternoon in Tromsø. This photo was taken in December.
References
- Burn, Chris. The Polar Night (PDF). The Aurora Research Institute. Retrieved 28 September 2015.
Other websites
- The polar night and polar darkness
- Many years' of webcam pictures from Tromsø, Norway. These clearly show the progression into and away from winter at a latitude within the Arctic Circle.
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