HSCI 3013 Exercise 8
Advising the Pope
The year is 1614. Due to the celebrity achieved by Johann Kepler as astronomer to Emperor
Rudolf II, you have been asked to advise the Pope on the appointment of a court astronomer in
Rome. His Holiness recognizes that he must select either a Ptolemaic astronomer, or a follower of
Copernicus or a follower of Tycho Brahe. He particularly requests your advice on the merits of
each view of astronomy, for the following subjects:
1) Is the view supported by known natural philosophy (Aristotle's physics)? If not, is there any other established position that would supply a physics to support the astronomy?
2) Is there an orb or sphere model available to explain the astronomical hypotheses?
3) Does the astronomy lead to acceptable predictions of positions for planets?
4) Does the astronomy allow the determination of the distances of planets?
5) Does the astronomy predict large variations in the apparent size of the Moon?
6) Is the astronomy consistent with the known facts about the motion and location of comets?
7) Does the astronomy predict that Venus should display phases?
8) Does the astronomy predict a parallax for the fixed stars (does it require an orbital motion of the Earth) ?
9) Is the astronomy consistent with the accepted explanation of the behavior of terrestrial objects like arrows and clouds (does it require a daily rotation of the Earth) ?
10) Does the astronomy employ an equant?
11) Is the astronomy consistent with scripture?
In each case establish whether the answer to the question counts as an asset or a liability for the astronomy in question. Use this comparison as the basis for your recommendation to the Pope.