Earth moves around the Sun more quickly than Mars. Every 26 months, Earth “laps” Mars on “the inside lane”. When Earth passes Mars, astronomers call the event an “opposition”. During an opposition, the Sun, Earth, and Mars form a straight line with Earth in the middle. Viewed from Earth, Mars is on the opposite side of the sky from the Sun. Opposition is the time in each 26-month cycle when Mars and Earth are closest together.