Original Description:
This animation shows how Earth and Mars move around the Sun in their orbits.
Click the "Play Fast" button in the lower left corner to make the planets move. For every second that goes by, the planets will move ahead one week's worth of time.
The other buttons make the planets move faster or slower, move backwards, or stop. The date in this simulation is shown above the buttons.
The "telescope view" in the upper left corner shows how big Mars looks from Earth through a telescope at a given time. The view only shows the size of Mars as viewed from Earth. It does not show how Mars changes in other ways over time, such as Mars spinning on its axis or the changing seasons on Mars.
Beneath the "telescope view" is a readout of the distance between Earth and Mars. Each time Earth passes close to Mars the event is called an "opposition". Notice how the size of Mars as seen through the telescope is not the same at every opposition. The orbit of Mars is not a circle; it is more of an oval in shape. Because an opposition can happen when Mars is at different points in its orbit, the distance at opposition changes, and so does the size of Mars as viewed from Earth. During the opposition in August 2003, 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).