The Antarctic Circle is creeping south by about 14.5 metres every year
The Antarctic Circle looks fixed on maps, but it moves. Its latitude depends on the tilt of Earth's axis, which wobbles by more than two degrees over 41,000 years under the Moon's pull. Right now the line is sliding south at roughly 14.5 metres a year.
Of the five main circles of latitude drawn on maps of Earth, the Antarctic Circle lies farthest south. Everything beyond it is the Antarctic; the band just north is the Southern Temperate Zone. It marks the northernmost place in the Southern Hemisphere where the centre of the Sun can stay above the horizon for a full day, so anywhere inside it sees the Sun at local midnight at least once a year and loses it at local noon at least once. The Arctic Circle plays the same role in the north.
The line currently sits about 66°33′51″ south of the Equator, a figure that ignores nutation, a small wobble worth up to 10 arcseconds. Because tidal forces from the Moon make Earth's axial tilt swing by more than 2° over a 41,000-year cycle, the circle migrates, and it is presently drifting poleward at about 14.5 m annually.
Standing exactly on the circle, one would in principle see the midnight sun only at the December solstice and total noon darkness only at the June solstice. In practice, atmospheric bending of light, mirages and the fact that the Sun is a disc rather than a point let part of the midnight sun show up to about 50 arcminutes, roughly 90 km, north of the line at sea level, with a matching effect southward in midwinter; higher ground extends these limits. Antarctic mirages can be dramatic, staging a string of false sunsets and sunrises while the Sun stays hidden.
The circle is about 16,000 km around and encloses some 20 million square kilometres, around 4% of Earth's surface and most of the Antarctic continent. Nobody lives there permanently. Scientists rotate through national research stations by season, and in earlier centuries some whalers stayed at semi-permanent stations for a year or longer. At least eleven children have been born in Antarctica, all at stations north of the circle.
Source: Antarctic Circle
