"I feel the earth move under my feet
I feel the sky tumbling down
I feel my heart start to trembling
Whenever you're around" -Carole King
I had so much fun earlier this week telling you about how we know that the heliocentric model is better than the geocentric one, that I thought I'd go a little farther down that rabbit-hole. You see, the first astronomical thing that any living creature likely notices is that, as seen from Earth, the Sun rises in the East each day and sets in the West.

I had so much fun earlier this week telling you about how we know that the heliocentric model is better than the geocentric one, that I thought I'd go a little farther down that rabbit-hole. You see, the first astronomical thing that any living creature likely notices is that, as seen from Earth, the Sun rises in the East each day and sets in the West.
The Sun, as it were, appears to move in half of a great circle throughout the sky. What's more, is that if you look up at night, you'll find that the night sky appears to move along a similar path, like the entire heavens rotates.
First off, the Earth could be stationary, and everything in the heavens, including the Sun, stars, Moon, and planets, could be revolving around it, once per day.
But if you have a perfect pendulum that lives on, say, a rotating planet, something very, very interesting happens.
So what happens if you do this?
The simplest way to do it is to build a long pendulum with a heavy mass, and tie it off at a small but significant (5-10 degree) angle. Leave it overnight. In the morning, come in and mark its position, and then burn the string you used to tie it off.
Why burn it? Because this way, you won't accidentally introduce any angular momentum; the pendulum will simply swing back-and-forth in a straight line.
Over the course of a day, they trace out a very telling pattern.
In fact, some people even videotape it...