Vernal Equinox

Sometimes, you just can’t trust your lying eyes. If you observe the sky, for example, you might see the Sun rising and setting every day and conclude that it circles around Earth. And that’s what most people thought until about five centuries ago. They were wrong, of course — their eyes deceived them.

Not everyone agreed with that idea, though. More than 2400 years ago, a Greek philosopher proposed that Earth, Sun, Moon, and planets all orbit the “central fire” of the universe. And a century later, Aristarchus of Samos concluded that the Sun was bigger than Earth. From that, he suggested that Earth orbited the Sun, not the other way around.

But neither man could produce evidence to back his idea. Since the eye suggested that the Sun was moving around Earth, that model held on for a long time.

It began to give way in the 16th century. Nicolaus Copernicus more fully developed the idea of a solar system with the Sun in the middle. And he described it with geometric equations.

Many educated people accepted the idea. And later, Johannes Kepler added better mathematical descriptions of how it works. So the idea of an Earth-centered universe gave way to one in which Earth orbits the Sun — regardless of what our eyes may tell us.

We’ll reach a key point in our annual orbit tomorrow — the vernal equinox. The Sun will cross the equator from south to north, marking the start of spring in the northern hemisphere. More tomorrow.

Script by Damond Benningfield