(not to scale)
Thanks to The Fraudulent Volcano blog
To see how an eclipse happens, get a flashlight or a candle (to be the sun), an orange (to be the Earth), and a ball about 1/4 the size of the orange (to be the moon). Put the orange and the ball on a table about eight inches apart from each other. Stand about two feet away from the ball, and hold the light at the same level as the ball and the orange, so they make a straight line. See how the shadow on the orange has a darker part and a lighter, less shadowed part?
The dark shadow is called the umbra (Latin for shadow). If you were on the Earth standing in the dark part of the shadow, you'd see a total solar eclipse. The lighter part is called the penumbra. If you were standing in the penumbra, you'd see a partial solar eclipse.