Page "Solstice" Paragraph 10

Also during the northern solstice, places on the Arctic Circle ( latitude 66. 56 ° north ) will see the Sun just on the horizon during midnight, and all places north of it will see the Sun above horizon for 24 hours.

That is the midnight sun or midsummer-night sun or polar day.

On the other hand, places on the Antarctic Circle ( latitude 66. 56 ° south ) will see the Sun just on the horizon during midday, and all places south of it will not see the Sun above horizon at any time of the day.

That is the polar night.

During the December Solstice, the effects on both hemispheres are just the opposite.