Antarctic Circle

Antarctic Circle is an imaginary circle on the earth which is parallel of latitude 66° 33ʹ south of the equator. South of the circle lies the Antarctic region. At the southernmost point the sun is visible on the southern winter solstice and at the northernmost point the midnight sun is seen on the southern summer solstice.

The position of the Antarctic Circle is not fixed. It is currently drifting southwards at a speed of about 15 m (49 ft) per year. Since the sun can remain continuously above the horizon for twenty-four hours on this circle, at least once each year at any location within the Antarctic Circle the sun is visible at midnight, and at least once the sun is not visible at noon.

The circumference of the Circle is roughly 16,000 km. The area south of the Circle is about 20,000,000 sq km covering roughly 4% of Earth's surface. Most of the continent of Antarctica is within the Antarctic Circle.

Further south the Circle the sun is seen above the horizon for many days, and at the South Pole, six-months ‘day’ starts on the autumnal equinox which is changed to six-months ‘night’ on the vernal equinox.