Time - Light and shadow (pre-visit)

Students examine the interplay of the earth and the sun by studying shadows. Students construct a sun clock and record shadows several times during a school day in order to use the earth and the sun to measure time.

A lesson plan for grade 3 Mathematics and Science

By Denise Young

Learn more

• Sundials a variety of links and resources relating to sundials
• Ancient Egypt webpage of the British Museum's Egypt exhibits
• Stonehenge information, pictures and legends

Related pages

• Getting an angle on light: Students will discover that the angle of the sun can mark time and is responsible for the color we see in the sky. Students will also understand that light can be reflected and refracted.
• The Earth rotates through days: The students will be a part of a model showing how the Earth's rotation creates what we see as a sunrise and sunset every twenty-four hours.
• Project Groundhog: The students will determine the groundhog prediction of either six more weeks of winter or an early spring and see if the prediction was accurate by recording daily weather data for six weeks. Over that six week period the students will be comparing their weekly data with schools around the USA and Canada using the Project Groundhog website.

Related topics

• Learn more about astronomy, environmental science, hands-on, mathematics, measurement, science, sun, sundial, and time.

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Learning outcomes

Students will learn:

• That the sun and earth can be used to tell the time of day.
• More specifically, that the shadow created as the earth rotates on its axis can be used to determine the time of day.
• How to construct a simple sun clock.
• How to record data about shadows and time of day using a sun clock.

Teacher planning

Time required for lesson

4 days

Materials/resources

• sun dial
• compass (for finding North)
• three or more copies of sun clock diagram for each student
• thirty copies of the rubric for student writing
• ten copies of group questions

For each pair of students:

• pencil
• round wheel (from tinker toys)
• stick/pencil (to place in center of wheel)
• flashlight (with wax paper rubber banded to the front to reduce glare)

Technology resources

Computers with internet access to use websites relating to extension activity (how other civilizations have kept track of the passage of time).

Pre-activities

Students should have some prior knowledge and experiences with light and shadows. Shadow searches throughout the school and grounds and shadow tag are some examples of pre-activities. Students should also know how to tell time to the hour prior to this lesson.

The teacher should preview supplementary websites to ensure their appropriateness for your students.

Activities

Important: These lessons will need to occur on a sunny day.

Day 1

1. Ask students to consider how they would tell time if they did not have a clock or watch. Students may discuss with a partner or respond in their journals.
2. Students share ideas with the class.
3. Discuss the sun as a “time teller.” Questions to consider: In which ways is the sun considered a “time teller?” What kind of time can you tell by the sun?
4. Show students the sun dial and ask what they know about it and how it works. Point out the base and the gnomen (the upright part). Demonstrate how the sun dial works by placing it on a sunny, level place outside and periodically observing how the light casts the shadow of the gnomen. Be sure that the sun dial is pointing north. It is easiest to orient the sun dial at noon.

Day 2

1. Provide directions to students about constructing their own sun clocks. Working in pairs, students will place the stick/pencil in the center of their wheel and place it in the box on the sun clock sheet. One part of their wheel should be touching the place where the box and the center line connect. Encourage students to trace their wheel once they have placed it so that it can be placed in exactly the same place later in the day.
2. Ask students to trace the shadow of the gnomen (stick/pencil in the center of their wheels) and record the time.
3. Ask students to predict where they think the shadow will be exactly one hour later and mark their prediction with an X on the white paper. As a whole class, ask students to explain their predictions.
4. Check students’ predictions one hour later. As a class, discuss the results and make predictions about future times during the day. Be sure to check the time using the sun clock at noon. (If all goes well, there should be a short shadow directly over the center line of the sun clock.)
5. Ask students to put their sun clocks in a safe place until tomorrow (or the next day the lesson is continued).

Day 3

1. Repeat the process of recording time using the sun clocks. Ask students to record the same times that the recorded yesterday using a new sun clock sheet.
2. At the end of the day, ask the pairs to compare their sun clock recordings. Are the tracings similar or different? Why? Ask students to write a paragraph explaining their reasoning on the back of their sun clock papers (each partner can write on the back of a different one). Students should attach them and turn them in for teacher review.

Day 4

1. In small groups of 3–5 students, students should discuss and complete the questions sheet.
2. Once the sheets are completed, hold a class discussion to check the answers.
3. Students should get in pairs (these pairings can be different than the previous partner work). Give each pair a flashlight (to serve as the sun) and give students several minutes to experiment with the flashlight and their sun clocks. Encourage students to use their sun clocks to recreate the times they recorded when they used the sun as their light source.

Extensions of this lesson: Study how other civilizations have kept track of the passage of time (Mayan and Egyptian Pyramids, Stonehenge, Sun Dials, Wyoming Medicine Wheel, etc.).

Assessment

• assessment of student writing from Day 3 (similarity of sun clock recording forms)
• Rubric
• Performance Assessment

Supplemental information

This lesson was adapted using ideas from a 6th grade unit called “Measuring Time” by the National Science Resources Center and published by Carolina Biological Supply Company, c. 1994.