Lesson 9: Early Cosmology

9. Lesson 9: Early Cosmology#

Wrestling With the Planets

"I was almost driven to madness in considering and calculating this matter. I could not find out why the planet would rather go on an elliptical orbit. Oh, ridiculous me! As the liberation in the diameter could not also be the way to the ellipse. So this notion brought me up short, that the ellipse exists because of the liberation. With reasoning derived from physical principles, agreeing with experience, there is no figure left for the orbit of the planet but a perfect ellipse." Johannes Kepler ( *New Astronomy, Based upon Causes, or Celestial Physics, Treated by Means of Commentaries on the Motions of the Star Mars, from the Observations of Tycho Brahe, Gent*, aka *Astronomia Nova*)

Everyone knows of the Galileo affair and Newton’s apple. But the details are important and in some of these cases tell slightly different versions. Our heroes are indeed Copernicus, Tycho, Kepler, Galileo, and Newton. Characters, all. Brilliant, all. The entirety of intellectual life changed after they were done and together they, with Descartes, form the cast of characters who led the Scientific Revolution.

In Lesson 4 we considered Galileo’s model of constantly accelerated motion. If that had been the only problem he’d solved, he would still have been a big deal in the textbooks. But he also discovered modern astronomy! Let’s review how views of the cosmos evolved before him and then let the big three: Galileo, Kepler, and Newton take us home to a working picture.

  Goals of this lesson:

Understanding, Appreciation, and Familiarity

  • Understand

    • Be able to explain what the important predictions were from Copernicus’ model and how they were confirmed.

    • Be able to explain how Kepler’s, Tycho’s, and Copernicus’ models of the solar system are different.

  • Appreciate

    • The ancient and Hellenistic Greek models of the solar system.

    • The Ptolemaic model.

  • Be familiar with

    • The lives of Copernicus, Kepler, and Tycho.

    • The importance of Tycho’s systematic approach to measurement.