What Am I Looking At – Part IV

“Ptolemy”

     by Aaron Clevenson

 

This is the fourth in a series of interviews with famous astronomers of the ages.  Our ultimate goal is to trace our understandings of the physical universe.  This month we are going to talk to Ptolemy.

 

NORTHSTAR:  Tell us a little about yourself.

PTOLEMY:  My name is Claudius Ptolemy.  I was born on the banks of the Nile (about 250 BC) in Ptolemais.  I have been charting the stars from an observatory right outside of Canopus, about 15 miles from Alexandria.

NORTHSTAR:  What contributions have you made to Astronomy?

PTOLEMY:  My greatest contribution is my book, Mathematical Syntaxis (the mathematical composition), often referred to as Almagest (Arabic for “the Greatest”).

NORTHSTAR:  What is so important about your book?

PTOLEMY:  In my book, I very accurately predict the motions of the sun, moon and stars more accurately than has ever been done before.

NORTHSTAR:  How did you achieve this accuracy?

PTOLEMY:  Well to begin with, the Earth is still the center of the Universe.  We have included small epicycles, little circular orbits superimposed on the orbits of the planets.  To this model we also included small eccentricities to improve the fit of the data.  Lastly, we have set the center of the planetary spheres in motion orbiting the Earth itself.  Are you still with me on this?

NORTHSTAR:  Isn’t this rather complex?  Do you really believe that all of these gears exist in the heavens?

PTOLEMY:  Well, yes it is complex.  The Universe IS complex.  No these gears and wires do not exist in the Heavens.  My model of the Universe is a representation used to predict the motions of heavenly bodies, not a representation of the actual physical Universe.

NORTHSTAR:  How big is the Universe?

PTOLEMY:  The Earth is but a mere speck in the grandeur of the Universe.  Unlike the ancients who believe you could build a tower to get a better view of the Heavens by being so much closer to them, we now know that the diameter of the Universe is about 100 million miles.  (Editor’s Note:  This would put the entire Universe inside the Earth’s Orbit as it is known in the year 2000 AD.)  At this size, the stars are moving at about 10 million miles per hour.  Any larger, and the stars would be moving at velocities that are not possible.

NORTHSTAR:  How do you know that the Earth is stationary in the center of the Universe?

PTOLEMY:  If the Earth were rotating, there would be great winds pushing in a single direction all the time.  If you were to throw a rock it would either fly off to a great distance, or not fly at all.  The same problems would be true if the Earth had any other motion as well.  Clearly what we see every day in our lives shows us that the Earth must be stationary.  What a foolish question.

NORTHSTAR:  Thank you Ptolemy for your time.  And thank you for helping to promote our knowledge and understanding of the Universe.