The video clips below were created to demonstrate why we see the phases of the moon. On the right you can see the set up that was used to simulate the Earth-Moon-Sun system. On the left you can see what the camera captured. Below these video clips is another QuickTime movie. This one is an animation that shows the phases of the Moon with a diagram of the Earth-Moon-Sun system beneath it. As the Moon goes through its phases, a red dot on the diagram follows the path of the Moon around the Earth. Use the movie controls to step back and forth through the animation to help you visualize what is happening as the moon goes through its phases.
A more detailed description of the phases of the Moon is also available.
Note: These demonstrations require QuickTime which is available for both the Macintosh and Windows platforms.
Earth-Moon-Sun system with Moon phases animation
The Sun is to the right of the Earth and Moon.