Even very clever guys can be very wrong about things until hindsight catches up to them.

[Aside: This, by the way, is a great source of comfort to guys like me, who are not so clever. It allows us to go, "Nyah". Schadenfreude.]

Ptolemy was an ancient astronomer. And a geographer. And a mathematician. And a poet. He was smart. He was one of the smartest men of his time. Many who came later stood on his shoulders.

He also believed that the sun and the planets went around the earth.

Today we call this the geocentric theory and laugh at it. Those days, they simply called it the truth.

To those bearded astronomers of yore, Earth was the Kanye West of planets. Standing in the middle, refusing to give up the mike, while the others planets hovered.

But, like I said, hindsight catches up. The first glitch that had people scratching their heads is the retrograde motion of the planets that supposedly revolved around the earth.

What is retrograde motion? OK, so grab a friend. And ask her to start walking around you in a circle. Tell her it is for science. As long as she keeps walking, she will always appear (to you) to be going in the same direction.

The same thing should happen to, say, Jupiter, If Jupiter revolves around Earth, then Jupiter should always appear--to someone on earth--to move in one single direction. Like any well-behaved planet should. But strangely enough to the ancient astronomers, Jupiter sometimes seemed to back up suddenly and start moving in the opposite direction in the night sky. This is retrograde motion.

And they couldn't explain it. The theory didn't fit.

Did Jupiter, like, suddenly go, "Oh wait, I think I left the gas on." and start scooting backwards? Well, planets are pretty darn big and look like a determined lot who don't change their minds often. So there had to be another explanation.

So quick, grab your friend again. Explain to her that, yes, the medications are still working and this is still a science experiment, and then both you and her starting walking around the kitchen table in the same direction.

A few steps into the lap, look over at your friend. She will appear to be moving in the same direction as you, as agreed. Now let's say that you are slightly faster than your friend. Eventually, you will "lap" her. At the moment that you pass her, she will appear to be moving backwards. This is retrograde motion.

That kitchen table is, of course, the sun. And Earth and Jupiter both revolve around the sun. Earth goes around the sun quicker, because of the smaller orbit. Jupiter loses this "race" sometimes and gets lapped and appears to move backwards.

The heliocentric theory explained retrograde motion. The geocentric theory was ditched.

This is science. Clever men proposing clever ideas that other clever men overturn.

Fact: Ptolemy's geocentric theory was dominant for 1400 years. You read that right. One and a half centuries before it got a proper burial, when Nicolaus Copernicus proposed the heliocentric theory.

Tamaso ma Jyotir gamayo (From darkness, lead us to light)
Asad ma Sad gamayo (From ignorance, lead us to truth)