- Polyhedron (Wikipedia)
In geometry, a polyhedron (pl.: polyhedra or polyhedrons; from Greek πολύ (poly-) ‘many’, and ἕδρον (-hedron) ‘base, seat’) is a three-dimensional shape with flat polygonal faces, straight edges and sharp corners or vertices.
- Double star (Wikipedia)
In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes.