Twenty four hours is the length of any day on Earth.
Twenty-four, just as on every other day of the year.
On June 21, they are all dark hours.
North of the Antarctic Circle, geographies experience a mix of hours of sunlight and hours of no sunlight. At the Antarctic Circle, there is at least one 24-hour period of no sunrise/ sunset per year. At the Equator, these periods are about 12 hours each.
The Antarctic Circle is the northernmost latitude in the Southern Hemisphere at which the sun can remain continuously above or below the horizon for 24 hours.
the tilt of the earth's axis
Never.The Antarctic Circle marks the latitude on planet earth south of which at least one 24-hour period has no sunrise or no sunset.All latitudes north of the Antarctic Circle experience one sunrise and one sunset each day...until the latitude of the Arctic Circle, where the reverse occurs.
around June 21
Twelve hours of daylight on the Antarctic continent would be a phenomenon experienced in a narrow, circular band of geography between the Antarctic Circle and the South Pole. This phenomenon would occur midway between December 21 and June 21, and again between June 21 and December 21.
Northern
North of the arctic circle, or south of the antarctic circle
The Antarctic Circle
This phenomenon occurs because the Earth tilts away from the sun, and this is the day where the extent of that phenomenon is shortest: one 24-hour period.
North of the Arctic Circle and south of the Antarctic one, the periods of daylight and darkness both vary from zero to six months, during the course of a year.
The Antarctic Circle is the northernmost latitude in the Southern Hemisphere at which the sun can remain continuously above or below the horizon for 24 hours, which it does for one 24-hour period twice each year.