Arctic Circle

The Arctic Circle is the latitude near 66.5° north where the Sun can remain above or below the horizon for 24 hours at least once each year.

Axial tilt: The angle between a rotating body's spin axis and the perpendicular to its orbital plane. Earth’s tilt makes the Sun’s seasonal path cross the horizon continuously at this latitude.
Latitude: A geographic coordinate measuring angular distance north or south of the equator. The Arctic Circle is defined by its latitude, not by a physical feature.
Antarctic Circle: The southern polar circle, near 66.5° south, marking the limit of annual 24-hour daylight or darkness. It is the Arctic Circle’s counterpart in the Southern Hemisphere.
Arctic Circle Marker: A monument or sign marking the Arctic Circle at a particular location. Roadside markers make the abstract latitude visible at selected crossings.
Midnight Sun: A phenomenon in which the Sun remains above the horizon at local midnight for at least one day. North of the circle, summer brings at least one day with no sunset.
Earth's equator: The great circle halfway between Earth’s poles, dividing the planet into Northern and Southern Hemispheres. The circle’s latitude is measured northward from this reference line.
Arctic: The polar region surrounding the North Pole, defined by geography, climate, or ecological boundaries. The circle is one common southern boundary used to describe this region.
Arctic Circle Trail: A long-distance hiking route across Greenland between Kangerlussuaq and Sisimiut. Its name invokes the latitude that the route crosses near its western end.
Polar night: A period when the Sun does not rise above the horizon for at least 24 hours. North of the circle, winter brings at least one day with no sunrise.
June solstice: The June solstice is the moment when the Sun reaches its greatest northern declination. It brings the longest daylight and the midnight Sun at the northern polar circle.

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