Imagine you are an extraterrestrial looking at earth from beyond the solar system. See earth as a sphere circling the sun. At the December solstice, the sphere is dark. At the June solstice the sphere is light. At the March and September equinoxes, the sphere is gray, balanced between light and dark. See the movie with a resizable window.
Using the above movie
You need 
Flash 9
or higher to see the Flash animation. The looping
movie is about two seconds long, depending on
computer capability or how long you linger at
each stop before clicking the Play button.
You can control the movie by clicking the angular button controls at the bottom of the movie itself, or with the left and right arrow keys on your keyboard.
- To play the movie automatically, click the Play triangle in movie
- To stop the movie, click the Stop triangle, or Left or Right arrow in movie
- To go to the left, stop the movie; then click either the small Left arrow or your keyboard left arrow key and hold
- To go to the right, stop the movie; then click either the small Right arrow or the keyboard right arrow key and hold
Flash allows you to zoom in and out to see details of different areas. To zoom in, hold down the Ctrl key on the keyboard. Click the movie, and choose Zoom in from the menu. (Not sure which browsers support this. Firefox 2.0.0.3 on Macintosh shows the zoom in menu but tries to add bookmark instead of zooming.)
Source graphic. Back to 12 to 2012.