CHAPTER 12

I. Answer briefly. In the book, you were given contradictory advice: to include fairly implausible hypotheses in your list to be investigated, and to exclude them. What are the reasons why you're urged to do each?

1. Include

2. Exclude

3. Consider each of the following statements from the Galileo case study. In each instance say whether the statement was plausible or implausible in the given context. (You may want to ask, "Plausible to whom?") Was the hypothesis in fact excluded or was it investigated in a serious way? (You may want to ask, "Taken seriously by whom?") Discuss briefly.

a. The observations Galileo made with his telescope do not prove that the moon's surface is rough because actually the moon is encased in a pecfectly smooth, unchanging crystal sphere.

b. The claim that the earth moved in 1543.

c. The claim in 1611 that Venus waxed and waned because the fiery matter on her surface ebbed and flowed, thus appearing sometimes as a crescent and sometimes as a circle.

d.The claim that Galileo's telescope was trustworthy for astronomical purposes although it made some celestial bodies, such as the moon, look larger while it made the stars look, if anything, smaller.

Tycho Question

II. In comparing the Ptolemaic and Copernican systems in lecture, we discussed how each of them could (or could not) account for various observations. (The diagrams shown on the overhead projector were all taken from Kuhn.) In this question you are asked to use the same sort of analyses to show how well the Tychonic system compares with the above.

1. Draw a diagram showing the basic geometry of the Tychonic system. (Do NOT include any epicycles.) Include in your diagram the Earth, Moon, Sun, the five known planets, and the Stars. Use arrows to show motions. Draw a thick line under any bodies which are not moving. (You will need to use Kuhn as a resource.)

2. According to this diagram, would one predict that with extremely strong telescopes one might be able to observe stellar parallax? (Discuss briefly.) How well did this prediction match actual observations at the time of Galileo? (If you've forgotten what stellar parallax is, look it up in the index of Kuhn's book.)

3. Now draw a Tychonic diagram that shows only the Earth, Sun and Venus.

4. According to this diagram, would Tycho need an epicycle to explain the fact that Venus (sometimes called either the Morning Star or the Evening Star) ALWAYS appears to be close to the Sun? (If so, draw a diagram including the epicycle.) (Discuss briefly.)

5. Draw a Tychonic diagram for Earth, Sun and Venus which shows the relative position of Venus at 4 different times of the year. Chhose one position when Venus is quite far from the Earth and one when she is close to the Earth. (Your diagram will bear some resemblance to the diagrams Kuhn uses when he discusses the phases of Venus.)

6. According to this diagram would one expect Venus to ever look like a full moon? A new moon? If so, which would have the biggest apparent diameter? How well did these predictions match the observable evidence available at the time of Galileo? (Discuss briefly.)

7. Ptolemy originally introduced epicycles to give a qualitative account of retrograde motion. Copernicus did NOT need epicycles to account for the fact that planets sometimes appear to move backwards. What about Tycho? Does he need epicycles to account for retrograde motion?

CHAPTER 13

III. Answer briefly.

1. Suppose you have two plausible hypotheses for explaining something which do not contradict each other (e.g., the pub is closed and there is a test tomorrow). You check up on the first, and find out that It's true. Why it does it not follow that the first one is the explanation of why Fred is in the library?

2. Suppose you have two hypotheses for explaining something which do contradict each other (e.g., the Ptolemaic system and the Copernican system ). You check up on the first, (e.g., by observing the phase behavior of Venus) and conclude that it's false. Why does it not follow that the second one is the explanation?

3. Even though the Ptolemaic rival to Copernicus no longer seemed plausible by 1611, there still remained Tycho's geocentric alternative. Why did Galileo find the Tychonic system implausible?

4. Why did many astronomers and physicists at Galileo's time find the Copernican system implausible?

5. When the scientific community is faced with two rival hypotheses and cannot agree on which is more plausible, what should they do?