Spherical Angle. The inclination of one great circle to another. Can be measured by intercepted arc of a great circle to which they are both secondaries, or by angle between lines tangent to the circles at their point of intersection.
Spherical Sailing.* Methods of navigation that take into account the spherical shape of Earth - instead of assuming a plane surface. Term is obsolete; methods are comprised in great circle sailing.
Spherical Triangle. Area, on surface of sphere, bounded by arcs of three great circles. Spheroid. Solid that is almost, but not quite, a sphere. Its section is an ellipse, and not a great circle.
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