sphere, Ingeometry, theset of all points in three-dimensional space lying the same distance (the radius) from a given point (the centre), or the result of rotating acircle about one of its diameters. The components and properties of a sphere areanalogous to those of a circle. Adiameter is any line segment connecting two points of a sphere and passing through its centre. Thecircumference is the length of any great circle, the intersection of the sphere with any plane passing through its centre. Ameridian is any great circle passing through a point designated a pole. Ageodesic, the shortest distance between any two points on a sphere, is an arc of the great circle through the two points. The formula for determining a sphere’ssurface area is 4πr²; its volume is determined by (4/3)πr³. The study of spheres is basic toterrestrial geography and is one of the principal areas ofEuclidean geometry andelliptic geometry.