Homework #5

Historical Astronomy
Due 5pm Friday Oct 10

I. Greek Astronomers of Antiquity [2 pts]

  1. What is the difference between astronomy and astrology?
  2. What contributions to astronomy were made by Aristarchus?
  3. What important observational astronomical discovery was made by Hipparchus, and how did he accomplish this?
  4. How did Eratosthenes measure the circumference of the Earth?
  5. Why were Aristotle's views about the heavens adopted by scholars of the Middle Ages?
  6. What were the main features of the Ptolemaic model of the Solar System?

II. Nicolas Copernicus / Tycho Brahe / Johannes Kepler [2 pts]

  1. What motivated Copernicus to discard the Ptolemaic model?
  2. How did the Copernicus' model of the solar system differ from Brahe's model?
  3. How did each of these models explain retrograde motion?
  4. How did each model explain why Mercury and Venus always appear close to the Sun?
  5. A major argument against the heliocentric model was the lack of parallax observed for the stars. What is parallax, and why was this argument erroneous?
  6. What was Brahe's main contribution to astronomy?
  7. Describe Kepler's 3 laws of planetary motion. What is the main drawback of these laws for understanding the cosmos?

III. Galileo Galilei [2 pts]

  1. Why were the following discoveries of Galileo significant:
    (a) crescent and gibbous phases on Venus;
    (b) moons of Jupiter;
    (c) craters and mountains on the Moon;
    (d) spots on the Sun?
  2. How did Galileo measure the rate of falling objects?
  3. Summarize Galileo's main contributions to the science of mechanics.

IV. Issac Newton [2 pts]

  1. Explain quantitatively (i.e., mathematically) how Newton used the acceleration of an apple falling from a tree together with the acceleration of the Moon in its orbit around the Earth to conclude that gravitational force varies inversely with the square of the distance.
  2. What is the difference between weight and mass?
  3. Summarize Newton's main contributions to optics.

V. Scientific Method [2 pts]
In each of the sections above, scientists were trying to build upon previous ideas, and in some cases had to reject old theories outright because they did not account for the observations, or made too many unjustified assumptions. Yet these scientists were also affected by authority figures and the prevailing views of the day. Describe at least two cases where prejudices about how the universe 'should' be kept an astronomer from even greater discoveries.