MiddleSchoolPortal/Turning Points in Science: Copernican Revolution

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Turning Points in Science: Copernican Revolution - Introduction

This is the second publication in our series called Turning Points in Science, which highlights the history and nature of science. The first publication covers the topic of germ theory and the third, atomic theory.

Claudius Ptolemy's geocentric theory of the universe, proposed in 140 A.D., formalized what even preliterate humans had known intuitively: the sun went around the earth, the earth was stationary. The early astronomer’s earth-centered theory endured until the mid-16th century, that’s up to 1,550 years! This means the heliocentric, or sun-centered, theory of the universe is a rather young idea. How could an obviously wrong theory prevail for over one and a half millennia? How does any scientific theory become established and persist?

A theory that provides both adequate explanation, or cause, for known observations and predictive power for future events is easily assimilated. Ptolemy's theory fit the bill; it worked on many levels. It accommodated most observations of the known celestial bodies. It also accommodated the notion that human beings were supreme beings, "created in the image of God," and thus rightly positioned in the center of the universe. Why then did the theory become obsolete? Why does any scientific theory become obsolete? When new observations suggest incongruence with existing theories, the theories must be re-examined and modified to accommodate the new observations; such is the nature of science. If the necessary modifications negate the original theory, it must be discarded and a new theory put in its place, which was the fate of Ptolemy's geocentric theory.



In his theory, Ptolemy had to account for observations that suggested some celestial bodies move with varying speed and apparently sometimes reverse their paths! Each complication represented an opportunity for falsification; one reason why the best scientific theories are simple and generalized. The geocentric theory also rested upon false assumptions, such as the "fact" that the paths of heavenly bodies are perfectly circular and the earth is at rest, notions promulgated by Aristotle and thus "true" by authority. These facts were not disconfirmed until technological innovation allowed.

This story of how one radical theory supplanted another illustrates and exemplifies the history and nature of science, an important domain in the National Science Education Standards. In recommending the history of science as a component of science literacy, the American Association for the Advancement of Science said in Science for All Americans,

There are two principal reasons for including some knowledge of history among the recommendations. One reason is that generalizations about how the scientific enterprise operates would be empty without concrete examples. Consider, for example, the proposition that new ideas are limited by the context in which they are conceived; are often rejected by the scientific establishment; sometimes spring from unexpected findings; and usually grow slowly, through contributions from many different investigators. Without historical examples, these generalizations would be no more than slogans, however well they might be remembered. . . .

A second reason is that some episodes in the history of the scientific endeavor are of surpassing significance to our cultural heritage. Such episodes certainly include Galileo's role in changing our perception of our place in the universe; Newton's demonstration that the same laws apply to motion in the heavens and on earth; Darwin's long observations of the variety and relatedness of life forms that led to his postulating a mechanism for how they came about; Lyell's careful documentation of the unbelievable age of the earth; and Pasteur's identification of infectious disease with tiny organisms that could be seen only with a microscope. These stories stand among the milestones of the development of all thought in Western civilization. (Retrieved October 2, 2007, from

Turning Points in Science: Copernican Revolution is the second in a series regarding historic, pivotal scientific advances such as the elucidation of atomic theory and the germ theory of disease. To avoid the pitfall of isolating the history and nature of science from science content, these publications focus on specific scientific advances relevant to the NSES content standards in life, physical, and earth sciences. In this way, the science becomes personal and understandable as a human endeavor, and thus its impact on society is more easily conceived. A potentially useful tool will be Burke's Knowledge Web, which provides the connections between historic figures in science that enabled the advancement of science. Although an explanatory video is in beta version only at the time of this writing, users can view it and bookmark the site for future use.

As students become aware of the various methods of science — some unique to different disciplines — they will notice the methods’ unity in the use of logical argumentation based on empirical evidence. For example, in Turning Points in Science: Germ Theory, the methods included controlled laboratory exercises as well as field tests, yielding many observations which by induction led to generalizations, or theory. This theory enables prediction and deduction.

Methods in astronomy rely more heavily on field observations, induction, and mathematical modeling accommodating the observations. These models are theories that enable predictions, such as when certain heavenly bodies will be in what positions relative to each other, and deductions, such as there will be a solar eclipse if the moon passes between the sun and earth.

Pedagogically speaking, it is important to avoid the temptation of verification exercises. Rather, allow students to make their own "discoveries," to interpret their observations, to make logical inferences, and to derive supported conclusions. If properly modified and presented competently, laboratory exercises are discovery opportunities for students, allowing students direct experience with the nature of science and inquiry in science. The National Science Teachers Association's position statement on Scientific Inquiry provides guidance regarding how teachers can conduct inquiry teaching and what teachers can expect from students.

This publication focuses on the evolution of the heliocentric theory of the universe. Resources provided here will facilitate understanding of the early concepts of the universe; the thinking that led to hypotheses in astronomy; the observations and experiments that yielded information allowing for theorizing; reaction to and acceptance of the investigators' findings; and the impacts of the theory on humanity.

In the Background Information for Teachers section of Turning Points in Science: Germ Theory are a number of resources that will be helpful here but are not repeated here. They include research articles on naive conceptions, how to conduct inquiry teaching, and a video description of the nature of scientific theory. The Background Information for Teachers of this publication provides resources that show how science does not progress in a vacuum, but within the cultural parameters of a society. Historical Figures in Astronomy offers an overview of individuals whose work impacted the evolution of the heliocentric theory.

The Lessons on Theories of the Universe and Lessons in Modern Cosmology are meant to help students understand the context, the emergence, and the impact of the heliocentric theory of the universe, touching on the NSES content standards of History and Nature of Science, Science in Personal and Social Perspectives, Earth and Space Science, and Science as Inquiry.

Background Information for Teachers

Scientific literacy includes knowledge of the history and nature of science. Resources in this section will assist you in first determining a sequence and then in dispelling widespread and current public misconceptions about the nature of our planetary system. Resources also examine some of misconceptions of the past.

For guidance in sequencing lessons, use the NSDL Strand Map Service. These maps illustrate connections between concepts and across grade levels. An image of the middle grades (6-8) only part of the Solar System map appears below. Under that is the K-12 Copernican Revolution map, One of nine under the heading Historical Perspectives. Clicking on a concept within the maps will show NSDL resources relevant to the concept, as well as information about related AAAS Project 2061 Benchmarks and National Science Education Standards. Move the pink box in the lower right hand corner of the page to see the grades 6-8 learning goals.

A Private Universe This site describes and provides access to a video documentary (20 mins.) on education research for grades 5-12 educators. The documentary explores why so few students grasp basic science concepts and traces the problem through interviews with Harvard graduates, their professors, and a ninth-grader who has some confused ideas about the orbits of the planets. This site also provides information about workshops and other materials.

Teachers' Domain: Seasons on Earth This lesson, though intended for grades 6-12, helps to dispel two popular misconceptions of what causes the seasons. Thus, it is a good companion to the Private Universe resource described above. It includes satellite data showing seasonal changes of plant life and explores an example of long-term natural climate change.

Examine Eclipsing Binary Stars from Several Perspectives A binary star was one of the observations that ancients strived to explain. Not knowing they were actually observing two stars in motion around each other, the ancients' "best guesses" worked as satisfactory explanations, given the limited "data" they had on which to base their inferences. This animation shows students how scientists study stars in a binary system. The introduction explains that, while it may not be possible to see both stars, their combined luminosity decreases as they eclipse each other. The animation, which shows a bright star with a smaller, dimmer companion star, demonstrates how such variables as the stars' brightness, size, and alignment alter the luminosity pattern. Students see the system from three perspectives simultaneously: a side view with a complete eclipse, an oblique view with a partial eclipse, and an overhead view with no eclipse. Each view also includes a graph that plots the pattern of luminosity over time. Movie controls allow students to repeat, pause, or step through the animation, which can give students more time to analyze the images.

Astronomy Without a Telescope Astronomy Notes is a resource for introductory astronomy classes for undergraduates. This section describes the celestial sphere, coordinate systems, and the motion of the stars. There are also sections describing time, the seasons, time zones, the phases of the moon, solar eclipses, lunar eclipses, and the motions of the planets.

The Reason for the Seasons Why the earth has seasons is one of the most difficult concepts for middle school students to understand. This publication provides resources to help teachers uncover their students’ misconceptions about the seasons.

The Age of the Universe, Dark Matter, and Structure Formation This collection of papers is the outcome of a colloquium addressing the three interconnected problems that have the center stage in modern physical cosmology. The problems are: the age of the universe; the dark matter of the universe; and the formation of structures in the universe. In the last two years, new experimental and observational data have dramatically changed the nature of each of these problems and have more sharply defined the issues. This National Academy of Sciences colloquium brought experts together to present cutting-edge developments and to emphasize the interdependence and interdisciplinary nature of the problems.

Stephen Hawking's Universe: Universes Menu Stephen Hawking discusses his ideas regarding the universe. He says, "For thousands of years, people have wondered about the universe. Did it stretch out forever or was there a limit? And where did it all come from? Did the universe have a beginning, a moment of creation? Or had the universe existed forever? The debate between these two views raged for centuries without reaching any conclusions. Personally, I'm sure that the universe began with a hot Big Bang. But will it go on forever?"

Astronomy Instruments This page contains links to one-pagers on historical instruments of astronomy with photos of the following: astronomical slides, celestial globe, cometarium, slated globe, Gregorian telescope, Kepler's Laws demonstration, orrery, planetarium, planisphere, stereoscopic pictures of the moon, tellurian, and transit.

Historical Figures

In this section we highlight individuals who have contributed to the fields of astronomy and cosmology. Looking across their contributions, one can see how the knowledge of one astronomer built upon the work of others, a notion captured in Isaac Newton's famous quote: "If I have seen further it is by standing on the shoulders of giants." You may choose to share one or more of the historical figures with your students, or have teams of students investigate all of the individuals. Some sites in this section may be above the reading level of middle school students and will require guidance from you. You might ask: Can students articulate how each person's contribution relates to others'? How did each person's findings impact history, society, and culture?

History and Philosophy of Western Astronomy The introduction to this resource is followed by three sequenced pages describing the work of Plato, Aristotle, Ptolemy, Copernicus, and Brahe and enhanced with photos, animations, and maps. The final page includes a vocabulary and review questions.

Nicholas Copernicus A brief description of Copernicus's major contribution to astronomy is part of a larger project called Windows to the Universe. Along with a portrait of Copernicus, the page includes a link to the Ptolemaic model and links to other information.

Galileo’s Biography This biography page is from the larger Galileo Project, a comprehensive site on the work, life, times, and impact of Galileo.

BBC Historic Figures: Isaac Newton This concise biography includes an image of Newton and links to related external sites: a news article about a collection of Newton’s papers; The Newton Project web site; and a lengthy biography.

Understanding the Universe: Stargazers Appropriate for middle school readers, this page from the American Museum of Natural History features 10 scientists and astronomers, including Einstein and Hubble. Users click on pictures of the individuals to learn more about them.

Famous Astronomers and Astrophysicists This page chronologically lists dozens of astronomers and other scientists, beginning with Copernicus, categorized by the Classical period, Nobel laureates, and others. Years of birth and death are given along with a couple of sentences regarding the person's work. Each name is linked to a page with more information sources. Be warned that some of the links are no longer active. Even so, this list brings to one's attention the less commonly known scientists whose work nonetheless contributed to advances.

Stephen Hawking: A Life in Science 2nd Ed. With a career that began over 30 years ago at Cambridge University, Stephen Hawking may have done more than any other scientist to broaden our basic understanding of the universe. His theoretical work on black holes and his progress in advancing our knowledge of the origin and nature of the cosmos have been groundbreaking. This publication from the National Academies Press can be downloaded for a fee.

Lessons on Theories of the Universe

In this section, we provide resources to help you help students acquire a clear picture of the evolution of humans' ideas of the universe. In doing so, you reinforce the nature of how science knowledge is accumulated; that is, science progresses when people build on accumulated knowledge. Additionally, middle school students will be able to make connections to the world history lessons they typically experience in their social studies curriculum. You may find it helpful to consult with social studies teachers to ascertain what students know. Then, you can start your instruction there and bridge to the new material.

Build a Solar System Activity This activity provides instructions for making a scale model of the solar system and learning the real definition of space.

The Sun and the Earth Participation in this lesson positions students to compare ancient humans’ perceptions and models of the universe with our current perceptions and models. This lesson plan helps students understand the relationship between the Earth and the Sun and how this relationship affects observable phenomena on Earth, such as the seasons. Students will describe the differences between the four seasons and investigate why the seasons occur; diagram the Earth and Sun during different seasons; predict and find out what the weather is in different places; and write journal entries from the viewpoints of people living in different parts of the world.

Precession While this site gives historical context for a sophisticated concept, it also provides a lesson plan. About 2,000 years ago the Greek astronomer Hipparchus discovered that the position of the Sun at any season, measured against the background stars, migrates in a slow cycle of about 26,000 years. This precession of the equinoxes also shifts the position of the celestial pole (so that our pole star would not have been a good guide for the ancient Greeks) and is caused by the rotation axis of the Earth slowly moving around a cone. Precession may be one of several astronomical processes contributing to the ice ages, as proposed by the Serbian astronomer Milutin Milankovich. Click on Lesson Plan to find the related lesson plan.

Lessons in Modern Cosmology

The resources in this section rely heavily on information gathered using modern technologies such as the Hubble Space Telescope. They will facilitate student understanding of modern conceptions of not only our sun-centered solar system but also the universe beyond, which until recently remained a mystery to humanity.

Solar System This site is part of the space page of the BBC (British Broadcasting Corporation), and provides information about the Sun, the planets and their moons, asteroids, and comets. In travel-guide style, it tells “visitors” what to see, reasons to visit, how to get there, and local history of each body or type of object in the solar system. In addition, links for more detailed information as well as space games and puzzles are provided.

Sun-Earth Connection One of three divisions within the Office of Space Science at NASA, the Sun-Earth Connection has the primary goal of understanding the Sun, heliosphere, and planetary environments as a single connected system. The web site offers information on space missions, including the Living with a Star and Solar Terrestrial Probes programs, and the science and technology behind the missions. The image gallery contains some of the most incredible photos and illustrations of the Sun available online.

Amazing Space In this set of web-based activities for classroom use, the lessons are interactive and feature photographs taken by the Hubble Space Telescope. Each activity has an overview, lesson plan, links to the National Science Education Standards, science background, and other resources and links. Downloadable worksheets are included. Students can build their own Milky Way, play galaxy games, and collect solar system trading cards.

SMARTR: Virtual Learning Experiences for Students

Visit our student site SMARTR to find related science-focused virtual learning experiences for your students! The SMARTR learning experiences were designed both for and by middle school aged students. Students from around the country participated in every stage of SMARTR’s development and each of the learning experiences includes multimedia content including videos, simulations, games and virtual activities.


The FunWorks

Visit the FunWorks STEM career website to learn more about science-related careers including Astronaut and many others.

Latest Science News from the New York Times

NYT > Astronomy and Astrophysics

News about Astronomy and Astrophysics, including commentary and archival articles published in The New York Times.

NYT > Eclipses

News about Eclipses, including commentary and archival articles published in The New York Times.

National Science Education Standards

These are the National Science Education Standards content standards in grades 5-8 aligning with this publication's resources.

Science as Inquiry Content Standard A:

Understandings about Scientific Inquiry

  • Different kinds of questions suggest different kinds of scientific investigations. Some investigations involve observing and describing objects, organisms, or events; some involve collecting specimens; some involve experiments; some involve seeking more information; some involve discovery of new objects and phenomena; and some involve making models.
  • Current scientific knowledge and understanding guide scientific investigations. Different scientific domains employ different methods, core theories, and standards to advance scientific knowledge and understanding.
  • Mathematics is important in all aspects of scientific inquiry.

Technology used to gather data enhances accuracy and allows scientists to analyze and quantify results of investigations.

  • Scientific explanations emphasize evidence, have logically consistent arguments, and use scientific principles, models, and theories. The scientific community accepts and uses such explanations until displaced by better scientific ones. When such displacement occurs, science advances.
  • Science advances through legitimate skepticism. Asking questions and querying other scientists' explanations is part of scientific inquiry. Scientists evaluate the explanations proposed by other scientists by examining evidence, comparing evidence, identifying faulty reasoning, pointing out statements that go beyond the evidence, and suggesting alternative explanations for the same observations.
  • Scientific investigations sometimes result in new ideas and phenomena for study, generate new methods or procedures for an investigation, or develop new technologies to improve the collection of data. All of these results can lead to new investigations.

Physical Science Content Standard B:

Motions and Forces

  • The motion of an object can be described by its position, direction of motion, and speed. That motion can be measured and represented on a graph.
  • An object that is not being subjected to a force will continue to move at a constant speed and in a straight line.
  • If more than one force acts on an object along a straight line, then the forces will reinforce or cancel one another, depending on their direction and magnitude. Unbalanced forces will cause changes in the speed or direction of an object's motion.

Earth and Space Science Content Standard D:

Earth in the Solar System

  • The earth is the third planet from the sun in a system that includes the moon, the sun, eight other planets and their moons, and smaller objects, such as asteroids and comets. The sun, an average star, is the central and largest body in the solar system.
  • Most objects in the solar system are in regular and predictable motion. Those motions explain such phenomena as the day, the year, phases of the moon, and eclipses.
  • Gravity is the force that keeps planets in orbit around the sun and governs the rest of the motion in the solar system. Gravity alone holds us to the earth's surface and explains the phenomena of the tides
  • The sun is the major source of energy for phenomena on the earth's surface, such as growth of plants, winds, ocean currents, and the water cycle. Seasons result from variations in the amount of the sun's energy hitting the surface, due to the tilt of the earth's rotation on its axis and the length of the day.

Science in Personal and Social Perspectives Content Standard F:

Science and Technology in Society

  • Science influences society through its knowledge and world view. Scientific knowledge and the procedures used by scientists influence the way many individuals in society think about themselves, others, and the environment. The effect of science on society is neither entirely beneficial nor entirely detrimental.

History and Nature of Science Content Standard G:

Science as a Human Endeavor

  • Women and men of various social and ethnic backgrounds--and with diverse interests, talents, qualities, and motivations--engage in the activities of science, engineering, and related fields such as the health professions. Some scientists work in teams, and some work alone, but all communicate extensively with others.
  • Science requires different abilities, depending on such factors as the field of study and type of inquiry. Science is very much a human endeavor, and the work of science relies on basic human qualities, such as reasoning, insight, energy, skill, and creativity--as well as on scientific habits of mind, such as intellectual honesty, tolerance of ambiguity, skepticism, and openness to new ideas.

Nature of Science

  • Scientists formulate and test their explanations of nature using observation, experiments, and theoretical and mathematical models. Although all scientific ideas are tentative and subject to change and improvement in principle, for most major ideas in science, there is much experimental and observational confirmation. Those ideas are not likely to change greatly in the future. Scientists do and have changed their ideas about nature when they encounter new experimental evidence that does not match their existing explanations.
  • In areas where active research is being pursued and in which there is not a great deal of experimental or observational evidence and understanding, it is normal for scientists to differ with one another about the interpretation of the evidence or theory being considered. Different scientists might publish conflicting experimental results or might draw different conclusions from the same data. Ideally, scientists acknowledge such conflict and work towards finding evidence that will resolve their disagreement.
  • It is part of scientific inquiry to evaluate the results of scientific investigations, experiments, observations, theoretical models, and the explanations proposed by other scientists. Evaluation includes reviewing the experimental procedures, examining the evidence, identifying faulty reasoning, pointing out statements that go beyond the evidence, and suggesting alternative explanations for the same observations. Although scientists may disagree about explanations of phenomena, about interpretations of data, or about the value of rival theories, they do agree that questioning, response to criticism, and open communication are integral to the process of science. As scientific knowledge evolves, major disagreements are eventually resolved through such interactions between scientists.

History of Science

  • Many individuals have contributed to the traditions of science. Studying some of these individuals provides further understanding of scientific inquiry, science as a human endeavor, the nature of science, and the relationships between science and society.
  • In historical perspective, science has been practiced by different individuals in different cultures. In looking at the history of many peoples, one finds that scientists and engineers of high achievement are considered to be among the most valued contributors to their culture.
  • Tracing the history of science can show how difficult it was for scientific innovators to break through the accepted ideas of their time to reach the conclusions that we currently take for granted.

Read the entire National Science Education Standards online for free or register to download the free PDF. The content standards are found in Chapter 6.

Author and Copyright

Mary LeFever is a resource specialist for the Middle School Portal 2: Math & Science Pathways project, a doctoral candidate in science education at Ohio State University, and presently teaches introductory biology at a Columbus, Ohio local high school. She has taught middle school and high school science and is an adjunct instructor of biology and natural sciences at Columbus State Community College.

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Copyright November 2007 - The Ohio State University. Last updated August 22, 2010. This material is based upon work supported by the National Science Foundation under Grant No. 0424671 and since September 1, 2009 Grant No. 0840824. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.