Modeling Lunar Phases
How is the moon’s motion related to the moon's phases?
Background The moon revolves around Earth, just as Earth revolves around the sun. The
moon does not make its own light. Instead, it reflects light from the sun. As it orbits Earth, the
moon appears to change shape from night to night. This picture shows four different shapes you
can observe on the moon and the names used to describe them.
In this activity, you will develop and use a model to investigate how these shapes come about
due to the motion of the moon and its position relative to the sun and Earth.
Materials
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bright flashlight
two foam balls in different sizes (about 4 cm and 10 cm in diameter)
sharpened pencils or ¼" dowels
Pre-Lab Questions
1. Develop Models Read through the entire lab. Then think about the materials in the list.
What do you think each material could represent in your model?
2. Construct an Explanation Look at the images of the shapes of the moon. What do
you think causes the dark and light areas of the moon? Keep in mind that the moon
reflects light from the sun.
Safety
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Note the lab safety icons that appear as warnings within certain procedure steps. For an
explanation of the meaning of each icon, go to the Lab Safety information section of this
online course. Be sure to follow all safety procedures established by your teacher and your
school.
The Earth-Sun-Moon System Investigation • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
Procedure
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1.
Prepare your materials by carefully pushing one of the pencil points into the small
ball just far enough so the ball stays on the pencil point. Do the same with the large ball
and the second pencil.
2. Develop a Model You will model each shape of the moon as shown in the diagram
Shapes of the Moon. Start by discussing how you could model the shape called the First
Quarter. Decide where you could position the flashlight and foam balls to show the sun,
Earth, and moon in orbit. Where will you position the moon so an observer on Earth
would see the first-quarter moon?
3. Develop a Model Next, decide how to model the moon’s motion. How would you move
your materials to show the moon’s orbit around Earth? What will happen to the shape of
the moon as seen from Earth?
4. Develop a Model Decide how to model the full moon, the third quarter, and the new
moon. Where on its orbit does the moon take on each shape as seen from Earth?
5. Record your plans for modeling the phases of the moon. Review your plans with your
teacher before building and testing your model.
Analyze and Interpret Data
1. Develop Models In your model, where did you place the flashlight, large foam ball, and
small foam ball to model the first quarter moon?
2. Describe In your first-quarter model, what shape was the lit side of the model moon? How
would that shape appear to an observer on Earth?
The Earth-Sun-Moon System Investigation • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
3. Use Models How did you model the moon’s motion? How did the moon’s appearance
change as the moon moved?
4. Develop Models How did you model the full moon? How did you model the new moon?
How would the moon in each model look to an observer on Earth?
5. Use Patterns How was your model of the third-quarter moon similar to your model of the
first-quarter moon? How was it different? What causes these shapes look different to an
observer on Earth?
6. Make Observations Have you ever seen moon shapes other than those shown in Shapes
of the Moon? What were the shapes? How could you use your model to show them?
7. Construct an Explanation One lunar cycle includes all of the lunar phases. One lunar
cycle happens about every month. Use what you learned from your model to describe how
the motions of the moon lead to lunar phases that occur in a lunar cycle.
The Earth-Sun-Moon System Investigation • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
Teacher Support
Focus on NGSS Students will apply the following practices, ideas, and concepts in this
activity.
Science and Engineering Practices
Connect to the Core Idea s
Crosscutting Concept
Develop and use a model to describe
phenomena.
• Patterns of the apparent motion of
the sun, the moon, and stars in the sky
can be observed, described, predicted,
and explained with models.
• This model of the solar system can
explain eclipses of the sun and the
moon. Earth’s spin axis is fixed in
direction over the short-term but tilted
relative to its orbit around the sun. The
seasons are a result of that tilt and are
caused by the different intensity of
sunlight on different areas of Earth
across the year.
Patterns can be used to identify cause
and effect relationships.
-------------------------------------------------Connections to Nature of Science
Science assumes that objects and
events in natural systems occur in
consistent patterns that are
understandable through measurement
and observation.
Group Size Pairs
Class Time 35 minutes
Safety
1. Remind students to be careful as they handle sharpened pencils or dowels.
2. Remind students not to shine the flashlight directly into anyone’s eyes, to avoid looking
directly into the flashlight, and to be careful as they move around the darkened room.
Advance Preparation (20 minutes)
1. Obtain enough foam balls so that each pair has two.
2. Sharpen pencils or dowels.
3. Prior to doing the activity, determine how you can darken the room or area you will be using.
Alternative Materials
1. If students are working in larger groups or as a class, you could use a lamp without a
lampshade instead of individual flashlights.
2. If you do not have foam balls of suitable sizes, any other relatively lightweight small balls
could be used. Use clay or glue to attach the balls to pencils, dowels, or craft sticks. You
could also have students make balls out of clay.
Procedure Tips
1. Suggest that lab partners take turns so one observes while the other manipulates the model.
2. For best results, the flashlight should be about one meter from the balls.
3. Students will need to adjust the distance between their Earth, moon, sun, depending on the
size of the objects they use to represent them, to avoid interfering shadows.
TE Annotations
Pre-Lab Questions
1. The flashlight represents the sun. The larger foam ball represents Earth, while the smaller
foam ball represents the moon.
The Earth-Sun-Moon System Investigation • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
2. The moon reflects light from the sun, and because the moon is a sphere, light will only shine
on parts of it at one time. The light areas are where the sun’s light hits the moon. The dark
areas are where the sun’s light does not hit.
Analyze and Interpret Data
1. Sample Answer: The flashlight shone straight on the large foam ball. The small foam ball
was off to the side of the large foam ball, so half of it was lit.
2. Sample Answer: The lit side of the moon was a full circle, but an observer on Earth would
see only half of the lit side and half of the shadowed side, because the moon is off to the
side.
3. Sample Answer: I modeled the moon’s motion by moving the small foam ball around the
large foam ball. I made sure both foam balls stayed to the same side of the sun.
4. Sample Answer: I modeled the full moon by placing the flashlight, large ball, and small ball
in a line, with the large ball in the middle. That way, the whole lit side of the moon was
visible from Earth. I modeled the new moon by placing the small ball directly between the
flashlight and the large ball. That way, only the un-lit side of the moon faces Earth.
5. Sample Answer: The third-quarter moon was similar because it was off to the side, like the
first-quarter moon. It was different because it was on the opposite side of Earth. During the
third-quarter the sun is shining on the opposite side of the moon. Observers on Earth see
the same shape, but with the lit side on a different side.
6. Sample Answer: I have seen the moon make a crescent shape. I could model this by having
the small ball between the large ball and the flashlight, but a bit off to the side. An observer
on Earth would see only a small portion of the lit side.
7. Sample Answer: The moon revolves around Earth. As it does so, different parts of the
moon’s lit side become visible from Earth. We call the different shapes of the lit side of the
moon lunar phases. A single complete orbit includes all of the lunar phases and is called a
lunar cycle.
The Earth-Sun-Moon System Investigation • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.