Image 2:  Star Trails Over Mauna Kea, Hawaii

This long (roughly 2 hour) exposure photograph brings to life the slow but steady counterclockwise drift of stars around the celestial pole. Notice that the pole sits quite low in the sky compared to its position seen from Charlottesville, reflecting the fact that Hawaii is closer to the equator than Charlottesville. The ancient Greeks noticed this dependence of pole elevation on location north or south and they inferred from it, correctly, that the Earth was spherical. But the Greeks were less successful interpreting the reason for the star motions. In their geocentric picture, the daily movement of the stars resulted from the rotation of the outermost celestial sphere, carrying the stars around the central stationary Earth.

It wasn't until the mid-16th century that Nicolaus Copernicus argued for the true reason in his famous book, De Revolutionibus Orbium Coelestium (On the Revolution of the Celestial Spheres). It was the Earth that was spinning, not the heavens. We don't feel the merry-go-round's spin because it is too big and the motion too slow. But more subtle observations reveal our world is indeed spinning. As the Beatles' song tells us: "The fool [read: wise man] on the hill sees the sun going down; but the eyes in his head see the world spinning round." Next time you watch a sunset, try to see what the fool sees - the Earth turning, not the sun sinking.