Moon Gazing PREFLIGHT
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The following three questions refer to the material you were to read in preparation for the lesson.

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World Views


In the 3 applets above, you have the two competing "world views" for explaining the motion of the planet Mars against the stars. Ptolemy used "epicycles" or circles inside circles, (Applet 1) Kepler used ellipses centered on the Sun (Applet 2). The data that Ptolemy had to work with couldn't tell the difference between the two "world views". Kepler had the data from Brahe's observatory, which was much better than the Greeks (or Chinese, or Mayans or Aryans...). Compare the two predictions against the different quality data sets using the hidden buttons at the bottom (Applet 3). Now answer the following questions.

What explanation does Ptolemy have for "retrograde" or reverse motion of Mars? What exactly does his explanation "mean"?
What explanation does Kepler have for retrograde motion? Does it "mean" anything more than Ptolemy's explanation?
What purpose is there is making measurements of something that has already been measured? (Say, your eyesight, your weight, or your height)? What purpose is there in making more careful/accurate measurements of those same things?



honors extra

Occam's Razor, is a phrase used describe William of Ockham's dictum "Never multiply entities unnecessarily". E.g., never use two hypotheses where one will do. Scientists call this being "elegant" or "aesthetically pleasing". This is often given as the reason why Keplerian cosmogeny replaced Ptolemaic, since scientists say Kepler's model took fewer hypotheses. Occam's Razor is actually a mathematical statement, not artistic judgement, and in the past 10 years, Bayesian statistics has been used to calculate whose theory uses more hypotheses. However despite Occam's contribution in the early 1300's, Copernican or Keplerian cosmogeny was not immediately accepted, but took over a century to replace Ptolemy. This is true not just of Copernicus, but for almost all revolutionary theories. Thomas Kuhn wrote a famous book on the subject of "Scientific Revolutions" around 1960, how theories don't die, the scientists who believe them do.
Can you think of some rational arguments why, like Kepler's boss, Tycho Brahe, you might actually prefer the Ptolemaic system?




Below is a space for your thoughts, including general comments about today's assignment (what seemed impossible, what reading didn't make sense, what we should spend class time on, what was "cool", etc. If you would, please offer suggestions about improvements to the class, since the department chair is concerned about the new teaching style.):




You may change your mind as often as you wish. When you are satisfied with your responses, click the SUBMIT button.

I received no help from anyone on this assignment.