retrograde motion; apparent retrograde motion; retrogradation
In astronomy, the apparent backward motion of a planet against the fixed stars. The two senses are merged here because they describe the same phenomenon; 'retrograde motion' and 'apparent retrograde motion' are essentially synonymous in modern usage, with 'retrogradation' being a less common variant.
See also: 順行運動
Mars's retrograde motion lasts about two months.
Retrograde motion is seen when Earth overtakes an outer planet.