Marsglobe3

• Relative
The point Mars’ geocentric longitude is 180° different from the Sun's is known as opposition, which is near the time of closest approach to the Earth. The time of opposition can occur as much as 8½ days away from the closest approach. The distance at close approach varies between about 54 and about 103 million km due to the planets' elliptical orbits, which causes comparable variation in angular size. The last Mars opposition occurred on January 29, 2010. The next one will occur on March 3, 2012 at a distance of about 100 million km. The average time between the successive oppositions of Mars, its synodic period, is 780 days but the number of days between the dates of successive oppositions can range from 764 to 812.
As Mars approaches opposition it begins a period of retrograde motion, which makes it appear to move backwards in a looping motion relative to the background stars. The duration of this retrograde motion is about 72 days.