great circle

views updated May 08 2018

great circle A line on the surface of a sphere representing the circumference of a circle whose centre is coincident with the centre of that sphere. In making a stereographic projection, a horizontal (equatorial) projection of the sphere (i.e. as a plane at right angles to the N—S plane) is a primitive circle of given radius, and also a great circle. All other great circles are similar to lines of longitude. A line joining the points on the conceptual sphere at right angles to the horizontal plane will project on a stereogram as a straight line passing through the centre of the projection, with the N and S poles as its diameter, both of which plot coincidentally in the centre of the horizontal plane. See PLANE OF PROJECTION.

great circle

views updated Jun 08 2018

great circle Circle on a spherical surface, the centre of which is coincident with the centre of the sphere. On the celestial sphere, the Equator is a great circle, as are all meridians. The shortest distance between any two points on a sphere, great circles are used for mapping aircraft routes.

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