Pedagogy in Action > Library > Guided Discovery Problems > Examples > Phases and Eclipses of the Moon

Phases and Eclipses of the Moon

Author: Ann Bykerk-Kauffman . Department Of Geological and Environmental Sciences, California State University, Chico
Parts of this activity were modified from Activity A-3 of the chapter entitled "Our Moon's Phases and Eclipses" in Fraknoi (1995).
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This material was originally created for On the Cutting Edge: Professional Development for Geoscience Faculty
and is replicated here as part of the SERC Pedagogic Service.


In this activity, students use a light source, a polystyrene ball, and their bodies to model solar and lunar eclipses, the phases of the moon, and the revolution and rotation of the moon. By observing their models of these phenomena in three dimensions, reality-checking with their notes of their observations of the real moon, drawing simple diagrams and completing complex partial diagrams, students "discover" the causes of phases and eclipses and the period of the moon's revolution and rotation.

Learning Goals

In this activity, students confront their misconceptions about eclipses and lunar phases, come to understand the true causes of these phenomena, practice using simple physical models to solve problems, and develop their 3-D visualizations skills.

The specific content learning objectives are:

  • Demonstrate and illustrate how the relative positions of the sun, Earth and moon cause the phases of the moon as seen from Earth.
  • Given a drawing or photograph of the moon in any phase, be able to correctly name that phase and draw a diagram showing the relative positions of Earth, the moon and the sun for that phase.
  • Given a diagram showing any possible set of relative positions of Earth, the moon and the sun, determine the name of the moon phase and draw what the moon would look like in that phase.
  • State which way the moon revolves around Earth and describe a method for figuring this out.
  • Demonstrate why we always see the same side of the moon (the face side of the "man in the moon")
  • Demonstrate what causes lunar and solar eclipses.
  • Explain why eclipses don't happen every month.

Context for Use

This activity has been extensively tested, revised and retested in our Concepts in Earth and Space Sciences course for future teachers. It has also been tested successfully in a 4th grade class for gifted children. Thus it should work well in Earth science and astronomy courses from middle school to college level. This activity works best if students complete it before reading any explanations or receiving any direct instruction about the causes of eclipses or the phases of the moon. However, before completing this activity, students should observe and sketch the moon once a day for at least a month. These observations help students gain familiarity with the phenomena they are being asked to explain, spark students' curiosity, and provide the data needed to determine the direction of the moon's revolution around Earth.

Description and Teaching Materials

  • Student Handout for the Activity on the Moon's Phases and Eclipses (Microsoft Word 77kB Dec14 08)
  • Pop-up Moon Phase Diagram (Acrobat (PDF) 153kB Dec14 08)
  • Other materials needed:
    • One pencil and one 3 inch diameter Polystyrene ball per student. An ordinary Styrofoam ball will not do; the ball must be opaque. Suggested source: Molecular Model Enterprises, 116 Swift St., P.O. Box 250, Edgerton, WI 53334, (608)884-9877. Prices are under $1 each.
    • One paperclip and one 7/8 inch diameter Polystyrene ball per lab table
    • One overhead projector
    • A single light source in the center of a darkened room

Teaching Notes and Tips

This activity can be completed in two hours. Any whole-class discussion would require additional time. Students (and instructors) love the "Aha!" moment, early in the activity, when they can see the moon's phases on the polystyrene ball. Celebrate that moment with the students and, as appropriate, remind them of it as they work through the rest of the activity, which can be frustrating because it requires students to do a lot of 3-D visualization and to confront their misconceptions. For example, most students believe that the moon revolves around Earth from east to west and that its phases are caused by Earth's shadow. As students strive to answer the questions in this activity, they may revert back to their prior misconceptions and may need to be reminded and helped to use the polystyrene ball to model and visualize the questions. You may also need to remind students to refer to their notes and observations of the moon as they try to figure out which way the moon revolves around Earth.


At the end of this activity, I typically assess student learning by having student groups present their answers to the rest of the class. I divide the different parts of this activity among the student groups, assigning each group to prepare illustrations and orally present their part to the rest of the class. Each presentation is then followed by a whole-class discussion.

I also ask students questions that require them to apply and extend the knowledge gained from this activity to specific situations. Here are some example questions; click on each to get the full-sized version:

I give students practice answering these questions in low-stakes ConcepTests (using clickers) or on-line practice quizzes before asking such questions on high-stakes exams.

References and Resources

The following reasonably-priced, thick (400 and 180 sheets, respectively) loose-leaf notebooks contain a wealth of classroom-tested hands-on activities, resource listings, and teaching suggestions for teaching astronomy. They are aimed at K-12 teachers, but are also very useful for college professors.

An excellent animation that simultaneously shows the relative locations of the moon, Earth and the sun and a view of the moon from Earth can be found at the Exploring Earth web site, by McDougall Littell Publishing Company:

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