As we orbit the Sun, Mars seems to grow and shrink as it moves closer and then farther away. This simulation shows the Red Planet’s appearance when viewed through a powerful telescope from May 1, 2003, through December 31, 2003.

At the beginning of May, Mars is 147,623,179 km (91,728,619 mi) from Earth. Because it’s so far away, Mars looks very small. The disk is only 9.5 arc-seconds across. (Each degree in the sky is divided into 60 minutes, and each minute is divided into 60 seconds.) For comparison, the full Moon is about 30 arc-minutes (1/2 degree) across in the sky. This makes the Moon appear about 190 times larger than Mars, which is about the size of a quarter held up almost 1/3 mile away. Pretty small!

As we approach Mars, it seems to grow in size until August 27, 2003, the date of closest approach. At this time, with Mars only 55,755,126 km (34,644,564 mi) from Earth, the Red Planet has grown more than 2.5 times larger, to 25 arc-seconds (like a quarter held at 1/8 mile). Still too small for the naked eye, but much easier for amateur telescopes.

Even though you can’t see Mars change size without a telescope, you can see it change brightness. On August 27, Mars is more than seven times brighter than it was at the beginning of May. After that, we pull ahead of Mars in our orbit, the distance again grows, and Mars shrinks and dims. At the end of the year, Mars is 165,574,923 km (102,883,295 mi) from Earth and has shrunken to only 8.5 arc-seconds across.

The little white dots whizzing around the frame are Mars’ two rapidly orbiting moons, Phobos and Deimos. Since the frames of the movie are one day apart, you don't see them orbit smoothly. Phobos takes only about eight hours to orbit, and Deimos takes a little over 30 hours. Both moons are much closer to Mars than our Moon is to us.

Another thing to note is that Mars seems like it's rotating backwards. Most of the planets in the solar system rotate in a counter-clockwise direction as seen from above. So does Mars. This effect is because each frame of the movie is 24 hours apart. Mars takes about 24 hours 43 min to rotate once, so we are catching it a little before it completes one rotation in each successive frame. This makes it look like it's rotating the wrong way. You've seen the same effect in movies when the frame-rate (24 frames per second) almost matches the rotation rate of car wheels or wagon wheels. They look like they are turning backwards.