|Good question, Rachel.
Mars has day and night for the same reasons that Earth has day and night. Mars, like Earth, rotates on an axis. That means that the Mars is spinning like a top. As the planet spins, half of it is facing the sun, and the other half isn't. So the half that is facing the sun experiences daytime, and the othe half has nighttime. The planet spins around so the the same half is facing the sun every 24.6 (almost 25) hours. This is the same way that we see night and day, except Earth spins a little faster, so we have a complete day and night every 24 hours.
I hope this answers your question.
(republished on 07/19/06)