Cosmic Railroad Tracks: Great Circles
Any planar closed loop drawn on the surface of a sphere is necessarily a perfect circle, as a result of the sphere’s steady curvature. Such loops qualify as either “great” or “lesser” circles, and the distinction is defined in mathematics as follows. A great circle is formed by the intersection of a plane passing through the center of a sphere with the surface of that sphere. Any other circle, no matter what size, is lesser. The center of a great circle coincides with the sphere’s center. In short, a great circle is an equator—found in any angular orientation, but always around the fattest part of its sphere.
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