LEARN NC

a girl on the beach

In this lesson, students will learn how the Sun’s position in the sky affects the size, shape, and location of their shadows.

In this lesson, students will go outdoors at three different times during the school day to measure the lengths of their shadows. After recording how their shadows change in shape, size, and direction, they will connect this information to the Sun’s motion across the sky and properties of light and shadows.

Learning outcomes

After this activity, students should be able to:

  • Discover the location of the Sun based on the direction of a shadow
  • Describe why shadows always touch the body at the feet
  • Explain why shadows are on the west side when the Sun is in the east and vice versa
  • Observe that the closer the Sun is to the horizon the longer the shadow will be
  • Predict that, near midday, an object casts the smallest shadow because the Sun is near its highest altitude or distance from the horizon
  • Observe changes in the size and shape of shadows over time
  • Predict, based on observations of the Sun’s motion in the sky, the size and direction of shadows at various times of day

Teacher planning

Time required

3 45-minute sessions

Materials needed

Each pair of students needs:

  • Chalk (sidewalk chalk works best for this)
  • Measuring tape, meter stick, or yardstick
  • Compass

Teacher background information

This lesson explores the properties of light. A discussion on the nature and properties of light is a very natural extension to this lesson. Following are some essential facts if you wish to prepare a discussion for your students.

Because the “screen” touches the student at the feet, the shadow will always form an image connected to the student’s feet. It will extend from there in a direction opposite from the Sun. When the Sun is in the east in the morning, the shadow will extend to the west. When the Sun is in the west in the evening, the shadow will extend to the east.

In the lesson Lightness and Darkness in Space, students saw how the size and shape of a shadow changes when the orientation of the object and of the screen is altered. Here, the object is connected to the screen while the light source is moving. Of course, students will eventually learn that it is the screen — Earth — that is moving, carrying the student-object with it, but for our purposes here only the relative motion matters.

When the Sun is near the horizon, sunlight strikes the ground at an oblique angle, and the shadow will be long. When the Sun is nearly overhead, sunlight strikes the ground at nearly a right angle, and the shadow will be short. If the Sun were to be directly overhead (this does not happen in the United States), a person would create no visible shadow on the ground since the shadow of his entire body would fit into his footprints. The width of a person’s shadow can vary depending on the angle of the Sun since human bodies are typically wider than thick. If a person faces south, his shadow will be thickest at midday and thinnest in the early morning or evening.

Pre-activities

Prior knowledge

Prior knowledge is not essential to lesson. However, if taught in the context of the entire unit, students will draw both on their previous study of the Sun’s motion across the sky; on their understanding of the nature of light; and the way relative orientations and distances of a light source, object, and screen determine the size and shape of a shadow.

Preparation

  1. Find a location on the school grounds to trace and measure students’ shadows three times in one day (9 a.m., noon, 2:30 p.m.). A sidewalk or cement patio would work well. The location should have a relatively flat surface suitable for chalk-drawing. Traffic, both automotive and human, must be light enough that marks created in the morning are likely to remain visible in the afternoon. (If the location where students tracked the Sun in the lesson The Sun Moves in the Sky satisfies these criteria, this would be the best place to use so students will have an easier time making connections between the two lessons.)
  2. Create student teams with two in each team.

Activities

  1. Introduce the activity with the following challenge.

    The other day, I asked someone’s dad to explain why his shadow changed shape, size, and position from morning to noon to afternoon. The dad thought for a while and explained, “My shadow followed me and the Sun got closer and further away — making my shadow taller and shorter.”

    Explain to the students that this dad was wrong and is a little confused. Tell students, “We have been learning what causes a shadow and why shadows are a certain shape and size and appear in a certain direction. With your partner, brainstorm what you know or what this dad needs to know to answer the question of how and why your shadow changes size, shape, and location throughout the day. ”

    Students should write and illustrate their responses in their science notebooks for 5–7 minutes.

  2. Have groups share their responses with the class. Record the responses and any questions on the board. After you are done, have the class help you categorize each response into two groups:
    • L: Responses connected to the properties of light
    • M: Responses connected to measurement

    Keep these responses visible during the lesson. Continue to refer to the questions that need to be answered or the explanations that are scientifically correct to help solve the challenge. Be sure to clear up misconceptions that are listed on the board during the lesson with evidence from the activity.

  3. Take the class out to the location for shadow-tracing. Gather in a circle. You’ll notice the kids stepping on each others shadows. Let them have some fun and play shadow tag for several minutes. Re-assemble in a circle and ask what they notice about their shadows and the Sun. Students will begin to make the observation that their shadows are on the opposite side of their bodies that the Sun is on. Some will also notice their shadows are longer than their bodies. Take several responses.
  4. Explain that each pair of students has four tasks:
    1. Take turns facing south and tracing your partner’s shadow. Leave plenty of space between each tracing.
    2. Measure both shadow tracings and record your measurements in your science notebooks.
    3. Measure both your length and your partner’s length (height) and record in your science notebooks. Students can lay down beside their shadow tracings for measurement if they won’t get dirty.
    4. Calculate the difference between the body length and shadow length for each of you. Record in your science notebooks.
  5. Once everyone is finished with their measurements, have them sit down by their shadow tracings and answer the questions listed below.
    1. Where is the Sun in the sky? How many fists up from the horizon?
    2. Does the Sun’s position in the sky cause your shadow to be a certain size and shape?
    3. Does the Sun affect the location of your shadow? Explain how and why.
    4. Do you believe that the Sun, you, and your shadow are lined up in a straight path? Explain your answer. Include a drawing to illustrate your explanation.
    5. Later in the day the Sun’s position in the sky will change. From what you know about light and shadows, how will this affect or change your shadow’s size, shape, and location? Explain why your shadow will change.
  6. If this step is done early in the day, and depending upon the time taken to complete it, the shadows may have changed sufficiently by the time students are ready to return to class so that they can already see a difference between their shadow and their shadow tracing. If so, point this out as a hint of things to come.
  7. Repeat steps 4 and 5 near noon and again near the end of the day.
  8. Before going home, ask students to trace their shadows outside at home right before dinner or right before the Sun sets.
  9. Type up the student questions and responses from the board and print enough copies for each pair of students.
  10. At the beginning of the next day, distribute the print-outs of the student questions and responses. Allow the class to review their measurements and answers from the day before to see if they match any of the student questions and comments from yesterday. Have each student highlight in their science notebooks where they answered or added further explanations to someone’s question or beliefs from the day before.
  11. Review with the class how their discoveries from the day before will help them explain to the confused dad why and how their shadows change throughout the day.
  12. Have each student write and illustrate an explanation to the question, “Why and how does your body’s shadow change throughout the day?” The students will write these illustrated explanations in letter form to one of their partner’s parents or guardians and their partner will take it home that night. Ask, but don’t require, the parents or guardians to write a thank-you note or response.

Assessment

Pre-activity assessment

The pre-assessment for this lesson consists of the students’ drawings and writings in their science notebook as well as the class discussion. This pre-assessment is based on prior knowledge of the Sun, light, and shadow — especially from the earlier lessons in this unit.

Activity assessment

The activity assessment consists of steps 4 and 5 in the Activities section of the lesson.

  1. The four tasks repeated three times throughout the day with recordings in the science notebooks.
    1. Take turns facing south and tracing your partner’s shadow.
    2. Measure both shadow-tracings and record your measurements in your science notebooks.
    3. Measure both your length and your partner’s length (height) and record in your science notebooks.
    4. Calculate the difference between the body length and shadow length for each of you.
  2. The answers to questions in Step 5. These questions are also listed in the student worksheet below.
    1. Where is the Sun in the sky? How many fists up from the horizon?
    2. Does the Sun’s position in the sky cause your shadow to be a certain size and shape?
    3. Does the Sun affect the location of your shadow? Explain how and why.
    4. Do you believe that the Sun, you, and your shadow are lined up in a straight path? Explain your answer. Include a drawing to illustrate your explanation.
    5. Later in the day the Sun’s position in the sky will change. From what you know about light and shadows, how will this affect or change your shadow’s size, shape, and location? Explain why your shadow will change.
  3. Assessment activity
    Activity assessment
    Open as PDF (11 KB, 2 pages; also available as Microsoft Word document)

Post-activity assessment

The post-activity assessment consists of the illustrated letters students writes to their partner’s parent explaining, “Why and how does your body’s shadow change throughout the day?” The letters should be assessed before going home to parents.

Modifications

Activity Extensions

  1. Each student plots his or her data on a graph. Y axis being the shadow length and the X axis being the time of day.
  2. Try out the activity from Science Netlinks Modeling Shadows. Students build a cut-out neighborhood and place it outdoors to observe and record the shadow’s relation to the time of day, position of the Sun, and time of year.
  3. Present students with a diagram or animation of the Sun’s path in the southern hemisphere. Challenge them to compare this with their observations. The Sun’s path in the southern hemisphere is reversed relative to our observations — the Sun appears to move from right to left. This challenge foreshadows later lessons that introduce how the fact that Earth is round affects our observation of the Sun’s apparent motion. This challenge will likely puzzle students and keep them guessing. A promise that more will be explained later will build excitement and curiosity.

Supplemental information

Safety issues

Remind students once again never to look directly at the Sun.

Troubleshooting tips

Explain your expectations for teamwork and cooperation.

Critical vocabulary

angle
the figure formed from two lines extending from the same point; also, the measure of the degree to which the two lines “open” or fail to be parallel
alignment
three objects are in alignment if one straight line can be drawn passing through all three
similar
identical in shape but different in size, orientation, or position

  • Common Core State Standards
    • Mathematics (2010)
      • Grade 3

        • Measurement & Data
          • 3.MD.4Generate measurement data by measuring lengths using rulers marked with halves and fourths of an inch. Show the data by making a line plot, where the horizontal scale is marked off in appropriate units— whole numbers, halves, or quarters.

    • North Carolina Essential Standards
      • Science (2010)
        • 3.E.1 Recognize the major components and patterns observed in the earth/moon/sun system. 3.E.1.1 Recognize that the earth is part of a system called the solar system that includes the sun (a star), planets, and many moons and the earth is the third planet...

North Carolina curriculum alignment

Science (2005)

Grade 3

  • Goal 3: The learner will make observations and use appropriate technology to build an understanding of the earth/moon/sun system.
    • Objective 3.01: Observe that light travels in a straight line until it strikes an object and is reflected and/or absorbed.
    • Objective 3.02: Observe that objects in the sky have patterns of movement including:
      • Sun.
      • Moon.
      • Stars.
    • Objective 3.03: Using shadows, follow and record the apparent movement of the sun in the sky during the day.