Editing Tropic of Cancer (section)

==Drift==
[[File:Trópico de Cáncer en México - Carretera 83 (Vía Corta) Zaragoza-Victoria, Km 27+800.jpg|[[Mexican Federal Highway 83|Carretera 83]] (Vía Corta) Zaragoza-Victoria, km 27+800. Of the Tropic of Cancer's intersections with Mexican federal highways, this is the only one where it is precisely marked and the drift from 2005 to 2010 can be seen.|thumb]]

The Tropic of Cancer's position is not fixed, but constantly changes because of a slight wobble in the Earth's longitudinal alignment relative to the [[ecliptic]], the plane in which the Earth orbits around the Sun. Earth's axial tilt varies over a 41,000-year period from about 22.1 to 24.5 degrees, and {{as of|2000|lc=yes}} is about 23.4 degrees, which will continue to remain valid for about a [[millennium]]. This wobble means that the Tropic of Cancer is currently drifting southward at a rate of almost half an arcsecond (0.468″) of latitude, or {{cvt|15|m}}, per year. The circle's position was at exactly 23° 27′N in 1917 and will be at 23° 26'N in 2045.<ref>[http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.htm Montana State University: Milankovitch Cycles & Glaciation] {{webarchive |url=https://web.archive.org/web/20110806021244/http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.htm |date=August 6, 2011 }}</ref>

The distance between the [[Antarctic Circle]] and the Tropic of Cancer is essentially constant as they move in tandem. This is based on an assumption of a constant equator, but the precise location of the equator is not truly fixed. See: [[Equator#Geodesy|equator]], [[axial tilt]] and [[circle of latitude#Movement of the Tropical and Polar circles|circles of latitude]] for additional details.