Note to the teacher: This lesson plan is most suitable for HIGH SCHOOL PHYSICS AND EUROPEAN HISTORY classes.

Ptolemy, Copernicus, & the Church



The students will:

1) list differences in the diagrams of a geocentric universe and a heliocentric universe 

2) describe the religious impact of this change on man's conception of the universe and man's place within it 

3) describe the impact of the Copernican view on cosmology of the late sixteenth and seventeenth century 

Background Information

In social studies, as in science, it is essential that we recognize and distinguish between what we see and how we interpret what we see. There is a fundamental difference between describing an event and explaining its cause--in science, it's delineating the dynamics from the kinematics. Yet, students constantly confuse the two.

In order to arrive at a single consistent explanation assumptions and points of view must be concise. This exercise will illustrate the importance of frame of reference to the students' views.

First, a series of optical illusions will be discussed, then the causes of parallax will be used to illustrate a changing frame of reference. This will be applied to the problem of explaining the motions of celestial bodies like the sun, moon, planets, and stars. Since historically it made little difference scientifically whether sight lines were drawn from a geocentric or heliocentric point of view, the decision to support the Ptolemaic or Copernican system of the heavens was not a simple or straightforward matter.


Seeing is not Always Believing
            20 minutes









Discuss the differences between what is actually seen and what is perceived.


Common Data-Different Conclusions
           20 minutes



1) Have students follow these oral instructions:

a) Draw a circle

b) Draw a second circle so that the two circles are touching on one side only

c) Draw a third circle that intersects with one of the circles in only two places but does not intersect with the other circle

2) Compare the drawings the class has made. There will be many combinations, all of which were drawn using the same set of oral directions.


Geocentric and Heliocentric Retrograde Motion
            1 class period



In this activity, students take the part of planets, walking through patterns in an open area outdoors. Not only do they appreciate the similarities in the appearance of retrograde motion from two different perspectives, but the models for geocentric and heliocentric schemes of the ancient universe become more concrete and understandable.

For the Geocentric Model:

1) Student A is Earth, B (5 m away) represents the center of the epicycle (in theory, just empty space!), C (2.l5m away from B) represents a planet. Keep strings taunt during the whole exercise.

2) As B moves slowly around A, C should move around B somewhat faster, but each person needs to maintain a constant rate. Trees and school buildings represent the fixed distant stars.

3) Depending on time, have other students take the three roles.

4) Have the students answer the following questions: 

a) Compared to the "stars," how does the planet C appear to the earth to be moving? 

b) Does the speed of earth ever appear to change? 

c) Does the speed ever appear to earth to change? 

d) Is there any evidence of retrograde behavior in the planets motion? If so, when does it occur? How long does it last?

For the Heliocentric Model:

1) Using the same philosophy as above, place B 4m away from A, C is 6m away from A. A represents the sun, B the earth, C a superior planet (like Mars).

2) Earth and Mars should try to walk in step, but Mars takes shorter steps.

3) Holding both strings overhead, Earth describes the motion of Mars. Watch to see if the speed of Mars appears to reverse in direction.

4) Make sure students understand how retrograde behavior can be explained using two different models.

5) Further investigation: Set up for an inferior planet such as Mercury. Earth's orbit is 10m radius, Mercury's is 4m radius. Mercury takes two steps for every one by Earth.


The Church and the Theory
           2 periods


PROCEDURE: (consult attached material)

1) Using the overhead projector, hand out of diagrams, or drawings on chalkboard, a presentation and explanation of the two diagrams should be made. 

2) Using brainstorming, the students will list the differences between them. 

Ptolemaic Cosmos

Based on a general framework of Aristotelian physics which had dominated medieval thought, the concept of the Ptolemaic Universe was a mathematical non-observational approach. It was based on the following basic premises of ancient astronomy:

1) A geostatic and geocentric cosmos. The earth did not move and was the center of the universe as the sun and all planets revolved around it.

2) Celestial bodies possess uniform, circular motion around a central point.

3) Celestial bodies are composed of a fifth element, the quintessence.

4) The cosmos is finite.

Copernican Cosmos

Nicholas Copernicus (1473-1543) was a mathematical, not an observational, astronomer who sought to purify ancient astronomy, not to overthrow Ptolemy. By allowing the earth to move, many of the difficulties of traditional astronomy would be overcome. The Copernican system was based on the introduction of three celestial motions:

a) Diurnal (daily) rotation of the earth on its axis

b) The earth, and the planets revolve around the sun (heliocentric) 

c) A conical axial motion of earth to explain the fixed orientation of earth in space

Problems of the Copernican System

The main disadvantage of the Copernican system was its violation of Aristotelian physics--the physical problems involved with the a moving earth (why a rock thrown upward was not left behind by a moving earch) called for a new, as yet nonexistent, physics. 

Diurnal rotation of the earth on its axis as well as the geliocentrism of the universe were to meet considerable resistance from people who had been taught to believe that the earth was stationary and at the center of the universe. People using "common sense" could deny that the earth moved as there was no sense of motion. 

Protestant View of the Copernican System

The first religious leaders to denounce Copernicus for contradicting the Bible were Luther and Calvin, but they did not officially condemn him.

Martin Luther said, in his work, Tischreden:

There was mention of a certain new astrologer who wanted to prove that the earth moves and not the sky, the sun and the moon. This would be as if somebody were riding on a cart or in a ship and imagined that he was standing still while the earth and the trees were moving. So it goes now. Whoever wants to be clever must agree with nothing that others esteem. He must do something of his own. This is what that fellow does who wishes to turn the whole of astronomy upside down. Even in these things that are thrown into disorder I believe the Holy Scriptures, for Joshua commanded the sun to stand still and not the earth. (Crowe 174) 

Roman Catholic Views of the Copernican Universe 

By 1500, the dominant intellectual influence upon theology was Aristotle. Aristotelian terms were used to explain terms in church doctrine. The Ptolemaic universe was based on Aristotelian physics. When Nicholas Copernicus published his De Revolutionibus Orbium Coelestium in 1543, the Protestant Reformation had been going on for years. At first the Church followed a policy of nonintervention. By the year 1600 the Roman Catholic church was deeply involved in the Counter Reformation against Protestants trying to bring back those lost to Protestantism and strict interpretation of Church doctrine was essential. 

The Copernican Idea of a heliocentric universe raised more than questions about the literal interpretations of the scriptures. Some of the following could be raised: 

1. If there were more than one planet, would God have placed humans on only one? 

2. If all humans were descended from Adam, how could life on other planets be descended from Adam? 

3. Why would the Bible say that Joshua had commanded the sun to stand still if the earth moves and not the sun?


1267-1273 St. Thomas Aquinas writes Summa Theologica integrating Catholic theology and Aristotelian philosophy 

1517 Martin Luther posts his Ninety-Five Thesis which begins the Protestant Reformation 

1543 Nicolas Copernicus publishes On The Revolutions of the Heavenly Spheres

1571 Tycho Brahe develops instruments for precise astronomical observation and records positions of stars and planets. He creates a Tychonic System of the cosmos called geoheliocentric. Planets revolve around the sun, while the sun and planets still revolve around the central earth 

1600 Giordano Bruno, a famous Italian philosopher who had espoused Copernicanism and an infinite universe, was tried by the Inquisition and burned 

1609 Johannes Kepler publishes his first and second Laws of Planetary motion. (l) Planetary orbits are elliptical. (2) Planets sweep out equal areas in equal times 

1609 Galileo Galilei develops a telescope of 30X magnification and begins observations 

1619 Kepler announces his Third Law of Planetary Motion which stated that a planet's distance from the sun is related to the time it takes a planet to revolve around the sun (T2 d3)

1632 Galileo publishes his Dialogues on the Two Chief Systems of the World which popularized the Copernican system and articulated the concept of a world subject to mathematical laws 

1633 Galileo is denounced by the Inquisition and forced to recant his belief in Copernican theory 

1667 Sir Isaac Newton constructs the first reflecting telescope

1687 Newton publishes his Principia Mathematica which explained gravitation, contained the components of Newtonian Physics (matter, motion, space, attraction), and challanged the Aristotelian/Ptolemaic cosmos. 


Crowe, Michael J. Theories of the World From Antiquity to the Copernican Revolution. New York: Dover Publications, 1990 

Kagan, Donald. The Western Heritage. New York: Macmillan, 1983.

Kearney, Hugh. Science and Change 1500-1700. New York: McGraw-Hill, 1974 

Morrison, Philip and Phylis Morrison. Ring of Truth. Random House, 1987. (Video version also available) 

Rutherford, Watson, Rinehart and Winston. Project Physics. 1975.