antipodes

Antipodes are points on the Earth's surface that lie on opposite sides of the globe. If a straight line could be drawn from one point through the center of the Earth, it would strike the other point, known as the antipodal point or antipode. On a perfect sphere, the antipode of any location is uniquely defined; on the Earth's actual shape, an oblate spheroid, the exact location depends on the reference ellipsoid used to model its surface.

The mean distance between a point and its antipode is about 12,742 kilometers (the Earth's mean diameter). Using a spherical model this distance is constant; in more precise ellipsoidal models it varies slightly with latitude, but remains close to the diameter.

In practice, most antipodal points on land are in ocean; land-to-land antipodal pairs are relatively rare. The term antipodes is also used in a broader cultural sense: in European languages, "the Antipodes" often refers to Australia and New Zealand, viewed as the opposite region to Europe.

Antipodal points are used in geography, navigation, and geodesy to understand global relationships, radio and satellite coverage, and antipodal point calculations. The concept also appears in mathematics and puzzles, where it helps describe diametrically opposite positions on a sphere and related symmetry.

Etymology and history: antipode comes from Greek antipodos, from anti- 'opposite' and pous 'foot', historically recognized in ancient geography as the idea of a place directly across the world.