... The true anomaly f equals the polar angle f in polar coordinates with origin at the center of the motion (e.g. Sun or Earth). ... Mean Sun-Earth distance, used as scaling distance in the solar system. ... Because of its lightweight construction it needs no staging to achieve Earth orbit, but only drops two of its engines. ... When one of the frames is accelerated, however, the two are not equivalent: Earth rotating around its axis fits Newtonian mechanics, the Sun going around a fixed Earth does not...