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14. Sundials: Observing and Using Shadows
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See the Activity in Action Summary of Activity:
Students build sundials and observe changes in shadows over the course of one or more days. Students identify patterns in the shadows and discuss how shadows may be used to tell time. 

Duration of Activity:
This is a flexible activity and can be conducted in short increments over one to two days. Allow 30 minutes for students to build their sundials. Allow 15 minutes each time students go outside to position sundials, and collect data.

Student Prerequisites:
Students should have:

  1. Prior exposure to the topic of the Sun through reading and class discussions.
  2. Experience with measuring and tracing shadows. (See lesson 4)
  3. A basic under-standing of the Earth's rotation and how day and night occur

Materials:

  • 1 9-inch white paper plate per student
  • one 4-inch plastic straw per student
  • Regular and colored pencils
  • Rulers
  • Tape
  • Chalk
  • Scissors
  • Watch or clock
  • Work sheet to record observations

Teacher Preparation:
Allow time to locate a quiet, sunny area to set up sundials and to locate materials.

Work Sheets:

"Sundial" Work Sheets
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View Completed Student Work Sheets

 

 

Objectives:

Students will:

  1. Build sundials and observe shadows as the Sun's position changes over time.
  2. Measure shadows and note the position of the Sun.
  3. Identify patterns of change in the shadows. 
  4. Predict the length of shadows and where they will fall on the sundial.
  5. Share data with peers and discuss how sundials serve as clocks.

View National Standards AddressedGrade Level:
Grades 1-3

Procedure:

Building Sundials

  1. Explain to students that they will build sundials and collect data based on their observations.
  2. Modeling the steps to building the sundial will make it easier for young students to complete the task. Distribute plates, straws, pencils, rulers, scissors and tape to students.
  3. Ask students to find the center of the paper plate and mark it with a dot.
  4. With a pencil have students place 4 registration marks along the edge of the paper plate (see photos).  Make one mark longer than the others. These marks will help students reposition their sundials for taking measurements throughout the activity. 
  5. Ask students to make 4 1/2-inch cuts in one end of the straw section.   Flare out the cut portion of the straw tape it onto the center of the paper plate. The straw should perpendicular to the surface of the plate.
  6. Measure and cut the straw to a 2-inch length. (See photos)

Using the Sundial to Collect Data

Day 1:

  1. In the morning distribute pencils, rulers, chalk and sundials to students.
  2. Ask students to place their sundials in a sunny spot on the playground. Mark the playground with chalk at the 4 registration points on the edge of their sundials. Remember to make one of the chalk marks longer so the sundials can be correctly repositioned. (See photos)
  3. Have students carefully trace the straw's shadow with a pencil.  Ask them to darken in the shadow with the pencil and write the time at the tip of the shadow.
  4. Ask students to note where the Sun is in the sky. Warn them NOT to look directly at it.
  5. After tracing ask students measure the shadow length and fill in their data sheets.
  6. Students will take more measurements later in the morning, at midday, and in the early afternoon.
  7. At the end of the day, ask students to predict where they think shadows will fall in the late afternoon. Ask them to look at their sundials and guess where the shadow would be at 2 PM (or any other afternoon time). Using a red pencil, have them outline the predicted shadow on their sundials. 

Day Two:

  1. Return the sundials to their marked locations on the playground the next afternoon, align registration points, and see if the student guesses for the 2 PM shadow were correct.
  2. Students may trace the real shadow to help compare it with their guesses.

Post-Activity Discussion Questions:

Students use their data work sheets during this discussion.

  1. What did you observe? What did the shadows do?
  2. When was the shadow the longest? Where was the Sun?
  3. When was the shadow the shortest? Where was the Sun?
  4. Why do you think the shadows change length? How can you explain what you are observing?
  5. How could you use a shadow to tell the time of day?
  6. How accurate were your predictions? What could you do to make them more accurate?

Assessment:
Use the Sundial work sheet to assess your students' work.

Bibliography:
See related books and websites.

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