Retrograde motion explanation When taking a heliocentric model and following both Earth and Mars' orbits, Mars is in retrograde motion with respect to Earth only in the short period during which Earth is overtaking Mars. Why doesn't the retrograde motion continue even after overtaking?
 A: Text and images from Retrograde Motion of Mars
In this "retrograde" motion, neither planet is actually moving backwards; it only appears that way during the time that one laps the other.
Mars is retrograde for slightly less than 10 weeks every 2 years

The two planets are like race cars on an oval track. Earth has the inside lane and moves faster than Mars -- so much faster, in fact, that it makes two laps around the course in about as much time as it takes Mars to go around once.
About every 26 months, Earth comes up from behind and overtakes Mars. While we're passing by the red planet this year, it will look to us as though Mars is moving up and down. Then, as we move farther along our curved orbit and see the planet from a different angle, the illusion will disappear and we will once again see Mars move in a straight line.Just to make things a little more odd, the orbits that Earth and Mars follow don't quite lie in the same plane. It's as if the two planets were on separate tracks that are a little tilted with respect to each other. This causes another strange illusion.
Suppose you were to draw a dot on a sky map each night to show where Mars appears as it moves forward, goes through retrograde, and then resumes its forward motion. Connect the dots, and you'll draw either a loop or an open zigzag. The pattern depends on where Earth and Mars happen to be in their tilted racetrack orbits.


 

From one time that the Earth and Mars are on a line through the Sun (called being in "opposition") to the next opposition is 2.135 Earth orbits. It is in a short period including the time of opposition when Mars exhibits its retrograde motion to an observer on the Earth. The time period between oppositions is called the synodic period.

Obviously, any  plantarium type program will illustrate this far better than a text answer, if you put in the correct dates.
As noted in the diagram, such motion occurs at opposition, when Mars is opposite the Sun in the sky, and rises near sunset. (slightly modified from NASA SP-4212)

The retrograde motions of Mars and Uranus in 2003 (Tunc Tezel, apod031216)
A composite image created by superimposing images taken on twenty-nine different dates.
A: Think about it this way. You're in a car driving down a freeway. You see a car ahead of you. Your car is going faster than his. So as you proceed down the road and approach his car he appears to be going backward toward you. Now picture the car as you actual pass it. Wave to the driver. In no time you will see him slip into the back seat window. But notice once you pass him and he is now in the rear window he goes from going backward to going slower. He now is trailing or receding from you, but he is no longer going backward. Same thing happens in planets. Hope this made sense to you. 
