Antarctic Circle

Imaginary line on the surface of the Earth at 66°30S, marking the southernmost point at which the Sun can be seen during the summer solstice, and the northernmost point at which the midnight Sun can be seen in S polar regions.

like its northern counterpart, the Arctic Circle, the value is currently slowly decreasing over time, pushing the Antarctic Circle southwards with about 15 m per year). For everywhere within the Antarctic Circle, there is at least twenty-four hours of continuous daylight on the Summer Solstice in December, and at least twenty-four hours of continuous nighttime on the Winter Solstice in June. That is to say, one whole day during which the sun does not set, and one whole day during which the sun does not rise. This is because the earth is tilted at a 23.5 degree angle, and during the winter solstice, the southern hemisphere is tilted away from the Sun, meaning that the antarctic circle is completely tilted away from the Sun, hence it experiences 24 hour nighttime, and vice versa. Mirages on the antarctic continent tend to be even more spectacular than in arctic regions, creating, for example, a series of sunsets and sunrises while in reality during that period the sun was under the horizon all the time.

The area south of this circle is known as the Antarctic, and the zone to the north is the Southern Temperate Zone.

The continent of Antarctica forms a land mass covering much of the area within the Antarctic Circle.

There is no permanent human population on Earth south of the Antarctic Circle.