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Platonic solid
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<p>In <a href="/facts/Geometry/wTQf5ffQ">geometry</a>, a Platonic solid is a <a href="/facts/Convex_polytope/2pRHcRgC">convex</a>, <a href="/facts/Regular_polyhedron/HJ6oGyug">regular polyhedron</a> in <a href="/facts/Three-dimensional_space/KAqKWUbS">three-dimensional Euclidean space</a>. Being a regular polyhedron means that the <a href="/facts/Face_(geometry)/T2E6BTU4">faces</a> are <a href="/facts/Congruence_(geometry)/2tKJ6AhB">congruent</a> (identical in shape and size) <a href="/facts/Regular_polygon/ws89Nhpt">regular polygons</a> (all <a href="/facts/Angle/gFUTEQYq">angles</a> congruent and all <a href="/facts/Edge_(geometry)/3lFN6sEz">edges</a> congruent), and the same number of faces meet at each <a href="/facts/Vertex_(geometry)/ID3cea9z">vertex.</a> There are only five such polyhedra: </p> <table><tbody><tr><th scope="col"><a href="/facts/Regular_tetrahedron/7mkSrl6j">Tetrahedron</a></th><th scope="col"><a href="/facts/Cube/65lUaAqN">Cube</a></th><th scope="col"><a href="/facts/Regular_octahedron/G38q92xW">Octahedron</a></th><th scope="col"><a href="/facts/Regular_dodecahedron/xClYqhcp">Dodecahedron</a></th><th scope="col"><a href="/facts/Regular_icosahedron/1U93vmXV">Icosahedron</a></th></tr><tr><td>Four faces</td><td>Six faces</td><td>Eight faces</td><td>Twelve faces</td><td>Twenty faces</td></tr><tr><td></td><td></td><td></td><td></td><td></td></tr><tr><td><ul><li>Animation</li><li>3D model</li></ul></td><td><ul><li>Animation</li><li>3D model</li></ul></td><td><ul><li>Animation</li><li>3D model</li></ul></td><td><ul><li>Animation</li><li>3D model</li></ul></td><td><ul><li>Animation</li><li>3D model</li></ul></td></tr></tbody></table> <p><a href="/facts/Geometer/lg9o1Pjo">Geometers</a> have studied the Platonic solids for thousands of years. They are named for the ancient Greek philosopher <a href="/facts/Plato/sPedMo74">Plato</a>, who hypothesized in one of his dialogues, the <i><a href="/facts/Timaeus_(dialogue)/5HQDToh9">Timaeus</a></i>, that the <a href="/facts/Classical_element/LIzQ4aoX">classical elements</a> were made of these regular solids. </p>