"Let us take things as we find them: let us not attempt to distort them into what they are not. We cannot make facts. All our wishing cannot change them. We must use them."
John Henry Cardinal Newman

The Shadow Knows

Another "proof" that the Earth is a sphere was presented by an ancient Greek by the name of Eratosthenes. As the story goes, Eratosthenes was visiting Egypt during the summer solstice. He noticed that at noon the Sun would shine directly down a well casting no shadow. In the next year, again during the summer solstice but this time in Greece, he noticed that the sun would cause pillars to cast a shadow. Believing the Earth to be a sphere, he reasoned that he could calculate the circumference based on the angle of that shadow.
   C=d/a/360 (Circumference = distance / angle / 360º)

There was one small flaw with Eratosthenes' beliefs. He based his calculations with his understanding that the Sun was far enough away from the Earth that it's light was parallel on all places on the Earth. If the Sun is, as I have suggested, much closer, then a different explanation could account for the shadow's angle.

Here is a quick experiment you can try at home:
Suspend a light about 3 feet above a flat surface such as your desk. This light will represent the sun. Now balance a pen on end directly beneath the light. This pen will represent the well shaft Eratosthenes saw in Egypt. Notice the pen casts no shadow. Now balance another pen on end about 6 inches away from the first. This pen will represent the pillars Eratosthenes saw back in Greece. Notice that this pen does cast a shadow. Can you calculate the circumference of your desk top?

"Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passion, they cannot alter the state of facts and evidence."
John Adams