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). A lot of times It will be a polar night for the winter and the opposite happens in the summer.
- Burn, Chris. The Polar Night (PDF). The Aurora Research Institute. Retrieved 28 September 2015.
- 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.