A **great circle**, also known as an **orthodrome** or Riemannian circle, of a sphere is the intersection of the sphere and a plane which passes through the center point of the sphere, as opposed to a general circle of a sphere where the plane is not required to pass through the center. (A *small circle* is the intersection of the sphere and a plane which does not pass through the center.) Any diameter of any great circle coincides with a diameter of the sphere, and therefore all great circles have the same circumference as each other, and have the same center as the sphere. A great circle is the largest circle that can be drawn on any given sphere. Every circle in Euclidean space is a great circle of exactly one sphere.

For any two points on the surface of a sphere there is a great circle through the two points. The minor arc of a great circle between two points is the shortest surface-path between them. In this sense the minor arc is analogous to “straight lines” in spherical geometry. The length of the minor arc of a great circle is taken as the distance between two points on a surface of a sphere, namely the great-circle distance. The great circles are the geodesics of the sphere.

In higher dimensions, the great circles on the *n*-sphere are the intersection of the *n*-sphere with two-planes that pass through the origin in the Euclidean space **R***n*+1.

Read more about Great Circle: Earth Geodesics, Derivation of Shortest Paths

### Famous quotes containing the word circle:

“That three times five is equal to the half of thirty, expresses a relation between these numbers. Propositions of this kind are discoverable by the mere operation of thought, without dependence on what is any where existent in the universe. Though there never were a *circle* or triangle in nature, the truths, demonstrated by Euclid, would for ever retain their certainty and evidence.”

—David Hume (1711–1776)