How do we know that the Earth goes around the sun?

No, really. Take a moment.

"Certainly," one might posit, "we have pictures of the Earth doing such a thing. I've seen it it textbooks and watched movies of it on the internet." [1]

Sorry, no. No one has ever observed the Earth going around the sun. Actually, there is no place from which you could observe this happening. No matter where you positioned yourself, during its orbit Earth would eventually become a tiny speck of light against the backdrop of space. Every diagram you've seen in a book or on the internet has exaggerated the size of the planets so you could see them, or drawn lines where the planets would go that don't actually appear in space. So how do we know that the Earth orbits the sun?

One solution to the problem was posed by the ancient Greeks. At this time in history, almost everyone believed that the sun went around the Earth, but a few intelligent people set out to discover for certain which orbited what. [2]

The Greeks hypothesized that if the Earth moved around the sun, then the positions of the stars in the sky would change between when you viewed them on one side of the sun and when you viewed them on the other. This is called the parallax effect. They put it to the test, and it was determined after great length and process that the Earth is, in fact, the center of the universe because the stars are in exactly the same place all year round.[3]

It's easy to believe, though, isn't it; that the Earth sits still? After all, if we moved around the sun so quickly, wouldn't we fly off? Would we not feel the rush of wind on ourselves as we flew through the air around the sun?

For all we know, the Earth is flat.

For all we know, the Earth is flat. Right?

It may come as some surprise to know that when Columbus sailed his ship to America, nobody truly thought he would fall off the edge of this square-cornered flatworld.

The revelation that the Earth was a sphere wasn't a great one, and it didn't take anything but careful observation by any interested person to prove it. Ships at sea would disappear under the horizon at a distance because of the curvature of its surface. Even Aristotle noted the shape of the Earth by its shadow cast on the moon during a lunar eclipse 1800 years before Columbus sailed.

In 1543, more than 60 years before the telescope was invented, Copernicus provided mathematical evidence that it was easier to describe the motion of planets if they moved around the sun, rather than around the Earth. This discovery threw into turmoil the beliefs of nearly two millenia of religious and scientific thought.