14 DAY TRIAL // Viewed from Earth, in the last past weeks, Mars appears to have slowed down its movement across the sky, and it seems that on the night of November 15th it will look like it were standing still. That is not the case, though, since it's just an optical illusion, such as that which made the ancient people believe that the Sun and the rest of the universe were actually rotating around the Earth.
The 'wandering star', as the ancients called it, will reverse its trajectory across Earth's sky for the next eleven weeks, then turn back again towards East, on January 30, 2008. Although is seems unusual, all the planets in the solar system exhibit this 'retrograde motion' at one time or another, but for a long time ancient astronomers could not find a solution for this kind of behavior. Mars also appears to deviate from its normal course, the retrograde motion will appear to bring it above its regular trajectory, giving up the impression the Mars actually is traveling in a loop.
The apparent retrograde motion is a result of the movement of the planets around the Sun, or revolution. Planets situated closer to the Sun, like Mercury and Venus, spin faster around it, than planet Earth does. The same thing is happening to the planets beyond the orbit of the Earth, only that they move at slower speeds around the Sun. As a result of Earth's faster orbit around the Sun, we periodically overtake them, this is when retrograde motion is observed; our planet will make multiple orbits around the Sun in the time it takes for the outer planets of orbit it once.
The ancient Greeks believed that the Sun, Moon and the planets moved around the Earth in perfect circles, but they had difficulties representing and calculating the mysterious loop. They finally explained this anomaly, by placing the planets in orbits around the Earth that described smaller 'epicycle', circles whose center moves with its main orbital circle around.
This was until the Polish astronomer Nicolaus Copernicus, published in 1543 the book "De revolutionibus", which finally placed Earth in the orbit of the Sun, and gave the retrograde movement a coherent explanation. The same effect can be obtained while driving on the road and taking over another car. Both cars are traveling in the same direction, and one is driving at a higher speed. As they pass each other, there is a small moment in time in which the cars will appear to the standing still in relation to one another, then the slower moving car appears to move backwards.
Mars goes through apparent retrograde motion every 25.7 months.
