For the ship of this name, see HMS Endurance. For the concept in geometry, see Polar circle (geometry).
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The north polar circle on a polar projection.The polar circle as lines on a modified cylindrical projection.The Arctic circle in Finland, 1975.The Arctic circle in Norway at Saltfjellet mountain plateau in July 2003.
A polar circle is a geographic term for a conditional circular line (arc) referring either to the Arctic Circle or the Antarctic Circle. These are two of the keynote circles of latitude (parallels). On Earth, the Arctic Circle is currently drifting northwards at a speed of about 14.5 m per year and is now at a mean latitude (i.e. without taking into account the astronomical nutation) of 66°33′49.9″ N; the Antarctic Circle is currently drifting southwards at a speed of about 14.5 m per year and is now at a mean latitude of 66°33′49.9″ S.[1] Polar circles are often equated with polar regions of Earth. Due to their inherent climate environment, the bulk of the Arctic Circle, much of which is sea, is sparsely settled whereas this applies to all of Antarctica which is mainly land and sheltered ice shelves.
If Earth had no atmosphere then both polar circles (arcs) would see at least a day a year when the center of the Sun is continuously above the horizon and at least a day a year when it is always below the horizon – a polar day and a polar night as is the case for longer, within the circles. Up to and including the associated poles (North and South), known geographically as the frigid zones such duration extends up to half of the year, namely, close to the poles. Instead, atmospheric refraction and the Sun's light reaching the planet as an extended object rather than a point source means that just within each circle the Earth's surface does not experience any proper polar night, 24 hours where the sun does not rise. By these same two factors, just outward of each circle still experiences a polar day (a day in which the sun does not fully set).
The latitude of the polar circles is + or −90 degrees (which refers to the North and South Pole, respectively) minus the axial tilt (that is, of the Earth's axis of daily rotation relative to the ecliptic, the plane of the Earth's orbit). This predominant, average tilt of the Earth varies slightly, a phenomenon described as nutation. Therefore, the latitudes noted above are calculated by averaging values of tilt observed over many years. The axial tilt also exhibits long-term variations as described in the reference article (a difference of 1 second of arc (″) in the tilt is equivalent to a change of about 31 metres north or south in the positions of the polar circles on the Earth's surface).
^Obliquity of the ecliptic Archived 2017-06-12 at the Wayback Machine
A polarcircle is a geographic term for a conditional circular line (arc) referring either to the Arctic Circle or the Antarctic Circle. These are two...
The Arctic Circle is one of the two polarcircles, and the most northerly of the five major circles of latitude as shown on maps of Earth at about 66°...
known as polar day, is a natural phenomenon that occurs in the summer months in places north of the Arctic Circle or south of the Antarctic Circle, when...
its geographical poles (the North and South Poles), lying within the polarcircles. These high latitudes are dominated by floating sea ice covering much...
for more than 24 hours. This occurs only inside the polarcircles. The opposite phenomenon, polar day, or midnight sun, occurs when the Sun remains above...
true within the equivalent polarcircle in the Northern Hemisphere, the Arctic Circle. The position of the Antarctic Circle is not fixed and currently...
the December and June Solstices respectively). The latitude of the polarcircles is equal to 90° minus the Earth's axial tilt. The Tropic of Cancer and...
The PolarCircle Marathon in Kangerlussuaq, Greenland is an annual marathon (42.195 km or 26.219 mi) that has the distinction of being situated on 66 degrees...
whose reference meridian is the great circle through the given location and the Earth's poles and whose polar axis is the line through the location and...
A polar route is an aircraft route across the uninhabited polar ice cap regions. The term "polar route" was originally applied to great circle navigation...
a given circle is the transformation of each point in the plane into its polar line and each line in the plane into its pole. Pole and polar have several...
a is the radius of the circle, ( r , θ ) {\displaystyle (r,\theta )} are the polar coordinates of a generic point on the circle, and ( r 0 , ϕ ) {\displaystyle...
of US$8.3 million. Circle K settled a similar class-action lawsuit in 2015 as well. Fountain drinks at Circle K are sold in Polar Pop cups, previously...
location. As viewed from outside the polarcircles, the Moon, like all other celestial objects outside the circumpolar circle, rises from the eastern half of...
winter side of the equinoxes. Outside the polarcircles, where the angular distance from the polarcircle is less than the angle which defines twilight...
long period of twilight, lasting for a few weeks.[citation needed] The polarcircle (at 66°33′49.9″ north or south) is defined as the lowest latitude at...
Circle of latitude List of circles of latitude Polarcircle Arctic Circle Antarctic Circle Equator Tropic of Cancer Tropic of Capricorn Great-circle distance...
24 continuous hours at some point during the year Polar region, the region within the polarcircles, referred to as the Arctic and Antarctic South Pole...
works on the grounds of Miami University in Ohio, the temporary work PolarCircle and the permanent sculptureStar-Crossed. Holt's Solar Web (1984–89) was...
which a body rotates Polar climate, the climate common in polar regions Polar regions of Earth, locations within the polarcircles, referred to as the...
subtropical and temperate zones, which lie between the two tropics and the polarcircles. Weather fronts and extratropical cyclones are usually found in this...
raid, Wheeler authorized a 15-member planning group under the codename PolarCircle that convened on June 10. One of its members was an officer who would...
definition "Rows on the Polar Open Waters" applies only to pure rowing expeditions across major water basins above the PolarCircle in the Arctic or within...
23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout...
the temperate regions. Antarctica and the Arctic lie in the polarcircles. The polarcircles are imaginary lines shown on maps to be the areas that receives...
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