Winter Hexagon of one another by following various lines traced through various stars in Orion. The stars in the hexagon are parts of six constellations. Counter-clockwise around the hexagon, starting with Rigel, these are Orion, Taurus, Auriga, Gemini, Canis Minor, and Canis Major. Winter Hexagon The Winter Hexagon or Winter Circle/Oval is an asterism appearing to be in the form of a hexagon with vertices at Rigel, Aldebaran, Capella, Pollux, Procyon, and Sirius. It is mostly upon the Northern Hemisphere's celestial sphere. On most locations on Earth (except the South Island of New Zealand and the south of Chile and Argentina and
Dehn plane Dehn plane In geometry, Dehn introduced two examples of planes, a semi-Euclidean geometry and a non-Legendrian geometry, that have infinitely many lines parallel to a given one that pass through a given point, but where the sum of the angles of a triangle is at least π. A similar phenomenon occurs in hyperbolic geometry, except that the sum of the angles of a triangle is less than π. Dehn's examples use a non-Archimedean field, so that the Archimedean axiom is violated. They were introduced by and discussed by . To construct his geometries, Dehn used a non-Archimedean ordered Pythagorean field