This lesson is designed for middle school students with no previous knowledge of astronomy or the history of astronomy. I often prepare my images as a slideshow or printed, large size images for students to understand the story of the scientists behind the science we are studying. This lesson should take approximately thirty to forty-five minutes, depending on the amount of time you spend explaining the parallax shift.

Group Size:


Learning Objectives:

  • Understand the life of Nicolaus Copernicus
  • Describe the importance of retrograde motion in prompting a shift from the geocentric to heliocentric models of the solar system
  • Describe parallax shift and the role it played in the Copernican model

Guiding Question:

Why was the Scientific Revolution important and how did it contribute to progress?


Images of Copernicus and parallax shift. A laptop with projector or access to computers to view the videos of parallax shift.

Additional resources:

Books and Articles:


[Note: This lesson in its entirety with images can be found as an attached pdf and doc file.]

Lesson Summary:

  • Introduce the biography of Nicolaus Copernicus (students should have read about Copernicus last night, so this should be familiar)
  • Provide a brief description of Copernicus' problems with the geocentric model
  • Introduce the Copernican/Heliocentric model of the solar system proposed by Copernicus
  • Describe/demonstrate parallax shift and explain why it appeared to prove the Copernican model wrong

Lesson: Nicolaus copernicus: Proposing a heliocentric Solar system

Guided by the ancient texts and rebirth of scientific inquiry, scientists began to have serious doubts about the accuracy of Ptolemy’s geocentric model of the Universe and the necessity of Epicycles to explain planetary movement. One astronomer that doubted this theory was Nicolaus Copernicus (1473—1543).

Nicolaus Copernicus was born on February 19, 1473 in Thorn Poland. Nicolaus’ father was a wealthy merchant in Thorn, but died when Nicolaus was 10 years old. After that, Nicolaus was raised by his uncle. Copernicus’ uncle was extremely supportive of his studies and supported him financially through the University of Krakow. Nicolaus continued his studies in the humanities in Bologna, medicine in Padua, and law at the University of Ferrara until 1503. After his graduation, he returned to Poland to assume a position as a canon at the Frombork Cathedral. Copernicus eagerly applied all of his studies and contributed greatly to the church and to medicine. He also made time to pursue an interest he was extremely passionate about: astronomy.
By May of 1514, Copernicus had already published one paper on his opinion that the a rotating Earth revolving with the other planets about a stationary central Sun could account in a simpler way for the same observed phenomena of the daily rotation of the heavens, the annual movement of the Sun through the ecliptic, and the periodic retrograde motion of the planets. Copernicus’ idea was both radical and conservative. In his radical restructuring of the Universe, he had adhered to the Aristotelian and Pythagorean paradigms that the planets are solid spheres orbiting in perfect circular motion about the sun.

Copernicus’ model still used small epicycles to get the retrograde motion exact, however, they were neither as detailed nor as significant as they had been in Ptolemy’s model. He also defined an astronomical unit (1 AU, which we still use today) to be the distance from Earth to the Sun, although he couldn’t calculate that distance. Finally, he found that planets closer to the Sun moved more quickly than planets farther away from the sun. This observation helped him provide an explanation for retrograde motion.

Retrograde motion is simply the projected position of the planet on the background stars as the Earth overtakes it – retrograde motion is just an optical illusion! BUT! If the Earth were moving around the Sun, then the stars should appear to shift due to our looking at them from different angles.

This is a good time to demonstrate this video of parallax shift.

Another activity that quickly demonstrates Parallax shift is holding your finger in front of your face and closing one eye and then another. This is similar to the planet in the Parallax Movie being on the left side of the star and then the right side of the star.

But, no one observed a shift in the stars. So, the stars would have to be VERY far away, or Copernicus’ theory was just wrong. At the time, scientists felt that God would not have wasted so much space in the Universe, and there must be no shift at all and, therefore, the Earth is not in motion...or is it?


At the end of this lesson I ask students to respond to short answer questions and read chapter 4 "Tycho Brahe: Taking Heavens Measure" and chapter 11 "Poor Kepler," in The Story of Science Newton at the Center by Joy Hakim (Smithsonian, 2005).

The assessment can be found as a separate wiki page here, where there is also a pdf and doc version available for download.

Attached Files:

Nicolaus Copernicus Lesson (pdf)

Nicolaus Copernicus Lesson (doc)

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