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Concentric objects
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<p>In <a href="/facts/Geometry/wTQf5ffQ">geometry</a>, two or more <a href="/facts/Mathematical_object/Juhyow9M">objects</a> are said to be <i>concentric</i> when they share the same <a href="/facts/Center_(geometry)/oKPIwkY3">center</a>. Any pair of (possibly unalike) objects with well-defined centers can be concentric, including <a href="/facts/Circles/9fy5ggKn">circles</a>, <a href="/facts/Sphere/jywYLNM2">spheres</a>, <a href="/facts/Regular_polygon/ws89Nhpt">regular polygons</a>, <a href="/facts/Regular_polyhedron/HJ6oGyug">regular polyhedra</a>, parallelograms, cones, conic sections, and quadrics. </p><p>Geometric objects are <i><a href="/facts/Coaxial/Y4puzfrx">coaxial</a></i> if they share the same <a href="/facts/Coordinate_axis/Mtd0q4SP">axis</a> (line of symmetry). Geometric objects with a well-defined axis include circles (any line through the center), spheres, <a href="/facts/Cylinder_(geometry)/0wQPPr3k">cylinders</a>, conic sections, and surfaces of revolution. </p><p>Concentric objects are often part of the broad category of <i><a href="/facts/Whorl/v0cmNUew">whorled</a> patterns</i>, which also includes <i><a href="/facts/Spiral/4R331aba">spirals</a></i> (a curve which emanates from a point, moving farther away as it revolves around the point). </p>