Wendekreis

Wendekreis is the term used in geography to refer to the two latitudinal circles on Earth where the Sun can be directly overhead at solar noon. The two circles are the northern Wendekreis, also known as the Tropic of Cancer, at about 23.436 degrees north, and the southern Wendekreis, also known as the Tropic of Capricorn, at about 23.436 degrees south. The name Wendekreis literally means turning circle, reflecting the annual motion of the Sun’s apparent position in the sky due to the tilt of the Earth's axis.

Geographic significance: The Wendekreise mark the boundaries of the tropics, the region between them where the Sun can be at zenith at some point during the year. These circles serve as a climatic and cultural boundary, separating tropical regions from subtropical and temperate zones. The area between the Wendekreise experiences relatively warm temperatures year-round, with seasonal changes driven more by precipitation than by large temperature swings.

Solar geometry: The Earth’s axis is tilted by about 23.5 degrees relative to its orbit around the Sun. As a result, the Sun’s declination ranges from +23.436 degrees in the northern summer to −23.436 degrees in the southern summer. On the Tropic of Cancer the Sun is overhead at or near the June solstice, and on the Tropic of Capricorn at or near the December solstice. For latitudes inside the tropics, the Sun can be directly overhead on two days per year (one during the Sun’s northward movement and one during its southward movement); for the exact Tropics themselves, overhead occurs once per year.

See also: Tropic of Cancer; Tropic of Capricorn; Equator; Arctic and Antarctic Circles.