I’m reading Simon Singh’s The Big Bang at the moment (only because I’ve already devoured our current Skepchick Book). In the beginning, he discusses how the Greeks first began to scientifically determine the nature of our solar system using little besides logic, math, a stick, and a fingertip. For instance, if you go outside tonight and point your finger at the moon, you’ll see that your fingertip just covers it. That means the distance between your eye and your fingertip is a little scale model of the distance between Earth and the moon. If you know how big the moon and your fingertip are, and the distance between your eye and your fingertip, you can figure out the distance between Earth and the moon.
Of course, you should go out tonight and try this mini-experiment, mostly because at approximately 10:30 pm ET there will be a full lunar eclipse, when the shadow of Earth will fall over the moon. Here in Boston, the skies should be clear enough to see the moon turn orangey red, so I’ll be out in the freezing cold stretching my fingertip upwards and thinking about the distance.