Direct and Retrograde Motion of Planet Mars as seen from Earth; Animation!
As seen from the Earth, the Sun, Moon, and planets all appear to move along the Ecliptic. Unlike the Sun, however, the planets don't always make steady progress along the ecliptic. They usually move in the same direction as the Sun, but from time to time they seem to slow down, stop, and reverse direction! This retrograde motion was a great puzzle to ancient astronomers. Copernicus gave the correct explanation: all planets, including the Earth, move around the Sun in the same direction; retrograde motion is an illusion created when we observe other planets from the moving planet Earth.
Mars, is further from the Sun than we are, and it orbits the Sun more slowly than we do. From time to time we pass Mars, and when that happens, the planet seems to be moving backwards because we're moving faster than it is. At such times we naturally see the Sun and the planet in opposite parts of the sky; the planet is said to be in Opposition to the Sun. Opposition is a good time to observe an outer planet; it's above the horizon all night, and relatively close to the Earth.
From 17 April through 29 June 2016, the planet Mars will be in retrograde motion, Mars just passed its Opposition on 22 May 2016.