Physics PHYS 102

General Astronomy

Problem Set #2


After you finish this problem set, you should be familiar with:



synodic period

Kepler's Laws


geocentric cosmology


Newton's Three Laws of Motion

phases of the Moon

retrograde motion


Newton's Law of Gravity

sidereal time



Special Relativity




General Relativity


heliocentric cosmology



sidereal period



Please answer the following questions using sentences and paragraphs.  When it is helpful, please use diagrams and equations.

  1. Where in the sky would you expect to see a full Moon at midnight?
  2. If you see the Moon high overhead shortly after sunset, what phase is it in? Explain.
  3. if the moon moved about the Earth in an orbit perpendicular to the plane of the Earth's orbit?  What would the cycle of lunar phases be?  Would solar and lunar eclipses be possible under these circumstances?
  4. The next total solar eclipse visible in North America will take place on Aug. 21, 2017.   Use the NASA web site to answer the following questions.  This page links to the following maps:, (animated gif), and (Google maps).
  1. Roughly describe the path of totality on the surface of the Earth.  Where and when does the period of totality begin?  Where and when does it end?  How long does it last?  Through which statesdoes it pass? (To answer these you will need to look at the maps that link to the page above).
  2. Approximately when does the period of totality begin and end in Charlotte, SC?  In Salem, OR?
  3. Describe what the eclipse would look like from Buffalo, NY? 
  4. When is the next solar eclipse, partial or total, that will be visible from Houghton?  You may want to back up to  for this question.  Print out a map showing the path of totality.
  1. Geocentric and Heliocentric models.
  1. What is retrograde motion?
  2. With the aid of a drawing, demonstrate how epicycles can explain the retrograde motion of planets in a geocentric solar system.
  3. With the aid of a drawing, explain how the retrograde motion of planets occurs in a heliocentric model of the solar system.
  4. If both models can explain the retrograde motion of planets, why do astronomers believe the heliocentric model is correct?
  5. Why do you think the Catholic Church opposed the heliocentric model? Is there anything in the Bible that would support one model over the other?
  1. Is it possible for an object in the solar system to have a synodic period of exactly one year? Explain your answer please.
  2. Writew down Kepler’s Three laws and explain what they mean.  Try out the simulations at and  Describe each simulation, and explain how each one demonstrates one of Kepler's Laws. 
  3. Describe Einstein’s special theory of relativity. What are some of its predictions? Has it ever been tested? If so, what were the tests?
  4. An understanding of planetary orbits is vital to the navigator of a starship. While attending Starfleet Academy, Wesley Crusher is required to pass a test on starship navigation which has a section on planetary orbits. Just for fun, lets see how you would score on this section of the exam for Starfleet Navigator, Class I:

(excerpt taken from Starfleet Academy Exam File NS105-AAA with permission of executive committee)

Answer the following questions to the best of your ability:

  1. How did Newton’s approach to understanding planetary motion differ from Kepler’s?
  2. List and explain each one of Newton’s three laws. Explain Newton’s law of gravitation.
  3. Why is Einstein’s general theory of relativity a better description of gravity than Newton’s universal law of gravitation.



Here are some practice "figure it out rather than memorize" type questions.  They will not be graded as part of the homework (so don't turn them in), but they may be useful as you prepare for the test.  More questions like these can be found in the test practice folder at the library.


A full Moon will always be at its highest in our sky at about











When will the first quarter Moon rise, approximately?


6 A.M.


5 A.M.


6 P.M.





Suppose two asteroids are located at the same distance from the Sun.

  One asteroid has twice the mass of the other. According to Newton's

  law of gravitation (and ignoring all forces except that from the



the more massive asteroid feels half the force that the other



both asteroids feel the same force, because gravity acts equally

     on all objects.


the more massive asteroid feels twice the force that the other



neither feel any force because they are weightless in space.