This animation shows the orbital motions of Earth and Mars.
Click the "Play Fast" button in the lower left corner to make the planets move. They will advance at a simulated rate of one week per second.
(Note: If you cannot see the animation below, or it is not working properly, you may need to download the latest Flash player.)
The other buttons make the planets move faster or slower, move backwards, or stop. The date in the simulation is shown above the buttons.
In the upper left corner is a simulated view of Mars as seen from Earth through a telescope. This simulated view shows the relative size of Mars at different times; it is not an "actual view" of Mars. For example, it does not show Mars rotating on its axis or changes in the Martian seasons.
Beneath the "telescope view or Mars" is a readout of the distance between Earth and Mars. Astronomers call the closest approach (when Earth "laps" Mars on the "inside lane") between Earth and Mars an "opposition". Notice how the apparent size of Mars varies between successive oppositions. This variation is primarily a result of the ellipticity (non-circularness) of Mars's orbit. The distance between Earth and Mars at opposition can be less than 55 million kilometers, or more than 100 million kilometers, depending on where Mars is along its elliptical orbit when opposition occurs. The oppositon in August 2003 was an especially close one. At that time, Earth and Mars were closer together than they had been in thousands of years!
The red dot is Mars. Earth is blue, and the Sun is yellow. The locations of the planets are shown to scale, but their sizes are not (the planets are actually much, much smaller than the Sun).