The Antarctic Circle is the most southerly of the five major circles of latitude that mark maps of

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. The region south of this circle is known as the

Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

, and the zone immediately to the north is called the Southern Temperate Zone. South of the Antarctic Circle, the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

is above the

horizon The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all viewing directions based on whethe ...

for 24 continuous hours at least once per year (and therefore visible at solar midnight) and the centre of the Sun (ignoring refraction) is below the horizon for 24 continuous hours at least once per year (and therefore not visible at solar noon); this is also true within the

Arctic Circle The Arctic Circle is one of the two polar circles, and the northernmost of the five major circle of latitude, circles of latitude as shown on maps of Earth at about 66° 34' N. Its southern counterpart is the Antarctic Circle. The Arctic Circl ...

, the Antarctic Circle’s counterpart in the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

. The position of the Antarctic Circle is not fixed and, not taking account of the nutation, currently runs south of the

Equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

. This figure may be slightly inaccurate because it does not allow for the effects of

astronomical nutation Astronomical nutation is a phenomenon which causes the orientation of the axis of rotation of a spinning astronomical object to vary over time. It is caused by the gravitational forces of other nearby bodies acting upon the spinning object. Alth ...

, which can be up to 10″. Its latitude depends on the Earth's

axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbita ...

, which fluctuates within a margin of more than 2° over a 41,000-year period, due to

tidal force The tidal force or tide-generating force is the difference in gravitational attraction between different points in a gravitational field, causing bodies to be pulled unevenly and as a result are being stretched towards the attraction. It is the ...

s resulting from the

orbit of the Moon The Moon orbits Earth in the retrograde and prograde motion, prograde direction and completes one orbital period, revolution relative to the March Equinox, Vernal Equinox and the fixed stars in about 27.3 days (a tropical month and sidereal mont ...

. Consequently, the Antarctic Circle is currently drifting southwards at a speed of about per year.

Midnight sun and polar night

The Antarctic Circle is the northernmost latitude in the Southern Hemisphere at which the centre of the sun can remain continuously above the horizon for twenty-four hours; as a result, at least once each year at any location within the Antarctic Circle the centre of the sun is visible at local midnight, and at least once the centre of the sun is below the horizon at local noon. Directly on the Antarctic Circle these events occur, in principle, exactly once per year: at the

December December is the twelfth and final month of the year in the Julian and Gregorian calendars. Its length is 31 days. December's name derives from the Latin word ''decem'' (meaning ten) because it was originally the tenth month of the year in t ...

and

June June is the sixth and current month of the year in the Julian and Gregorian calendars—the latter the most widely used calendar in the world. Its length is 30 days. June succeeds May and precedes July. This month marks the start of su ...

solstice A solstice is the time when the Sun reaches its most northerly or southerly sun path, excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around 20–22 June and 20–22 December. In many countries ...

s, respectively. However, because of

atmospheric refraction Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height. This refraction is due to the velocity of light ...

and

mirage A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French ''(se) mirer'', from the Latin ''mirari'', mean ...

s, and because the sun appears as a disk and not a point, part of the midnight sun may be seen on the night of the southern

summer solstice The summer solstice or estival solstice occurs when one of Earth's poles has its maximum tilt toward the Sun. It happens twice yearly, once in each hemisphere ( Northern and Southern). The summer solstice is the day with the longest peri ...

up to about 50 minutes (′) () north of the Antarctic Circle; similarly, on the day of the southern

winter solstice The winter solstice, or hibernal solstice, occurs when either of Earth's geographical pole, poles reaches its maximum axial tilt, tilt away from the Sun. This happens twice yearly, once in each hemisphere (Northern Hemisphere, Northern and So ...

, part of the sun may be seen up to about 50′ south of the Antarctic Circle. That is true at sea level; those limits increase with elevation above sea level, although in mountainous regions there is often no direct view of the true horizon.

Mirage A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French ''(se) mirer'', from the Latin ''mirari'', mean ...

s on the Antarctic continent tend to be even more spectacular than in Arctic regions, creating, for example, a series of apparent sunsets and sunrises while in reality the sun remains below the horizon.

Human habitation

There is no permanent human population south of the Antarctic Circle, but there are several

research stations in Antarctica Multiple governments have set up permanent research stations in Antarctica and these bases are widely distributed. Unlike the drifting ice stations set up in the Arctic, the current research stations of the Antarctic are constructed either on ...

operated by various nations that are inhabited by teams of scientists who rotate on a seasonal basis. In previous centuries some semi-permanent

whaling Whaling is the hunting of whales for their products such as meat and blubber, which can be turned into a type of oil that was important in the Industrial Revolution. Whaling was practiced as an organized industry as early as 875 AD. By the 16t ...

stations were established on the continent, and some whalers would live there for a year or more. At least eleven children have been born in Antarctica, albeit in stations north of the Antarctic Circle.

Geography

The circumference of the Antarctic Circle is roughly . The area south of the Circle is about and covers roughly 4% of Earth's surface. Most of the

continent A continent is any of several large geographical regions. Continents are generally identified by convention (norm), convention rather than any strict criteria. A continent could be a single large landmass, a part of a very large landmass, as ...

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

is within the Antarctic Circle.

Sites along the Circle

Starting at the

prime meridian A prime meridian is an arbitrarily chosen meridian (geography), meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. On a spheroid, a prime meridian and its anti-meridian (the 180th meridian ...

and heading eastwards, the Antarctic Circle passes through: :

References

External links