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Daily Do

How Do Shadow Lengths Change Over Time?

Topics

Is Lesson Plan Physical Science

Levels

Middle School Elementary

Welcome to NSTA's Daily Do

Teachers and families across the country are facing a new reality of providing opportunities for students to do science through distance and home learning. The Daily Do is one of the ways NSTA is supporting teachers and families with this endeavor. Each weekday, NSTA will share a sensemaking task teachers and families can use to engage their students in authentic, relevant science learning. We encourage families to make time for family science learning (science is a social process!) and are dedicated to helping students and their families find balance between learning science and the day-to-day responsibilities they have to stay healthy and safe.

Interested in learning about other ways NSTA is supporting teachers and families? Visit the NSTA homepage.

What is sensemaking?

Sensemaking is actively trying to figure out how the world works (science) or how to design solutions to problems (engineering). Students do science and engineering through the science and engineering practices. Engaging in these practices necessitates students be part of a learning community to be able to share ideas, evaluate competing ideas, give and receive critique, and reach consensus. Whether this community of learners is made up of classmates or family members, students and adults build and refine science and engineering knowledge together.

Introduction

Today's task is the final in a series of elementary tasks about shadows. The first in the series, Why is my shadow always changing?, introduced two formative assessment probes, "Shadow Size" and "When is My Shadow the Longest", and shared strategies for using these (and other) probes to engage students in productive science talk and create the need to engage in science and engineering practices to make sense of phenomena. The second in the series of tasks, How can light make dark shadow and bright reflections?, students and families read the NSTA eBook The Amazing Light Show and notice a puzzling picture of a giant shadow cast by a very small cat. This creates the need engage ins science and engineering practices to figure out the relationship between the distance of the light source from an object and the size of the object's shadow.

That brings us to today's task, How do shadow lengths change over time?, in which students engage in science and engineering practices and use the thinking tools of patterns and cause and effect to make sense of the science idea that orbit of the Earth around the sun and the rotation of Earth on its axis causes changed in the length and direction of shadows.

Investigating Shadow Length

This task builds on an activity that was first published in the Why is My Shadow Always Changing? Daily Do. Refer to this Daily Do for background on using formative assessment probes with students.

Materials (per student)

  • When is my shadow the longest formative assessment probe (print or share screen)
  • meter stick or measuring tape (you will need two meter sticks if using one to cast a shadow)
  • chalk or masking tape to mark shadow length (optional)camera/cell phone or tablet with camera (optional)open space that receives sunlight all day like a parking lot, playground, park, or yard

You might say to your students, "I found this interesting picture picture of a young person and their shadow. What are some things you notice or wonder about this picture?" Give students a minute or two to individually record observation/questions (Alone Zone), and then ask them to share their noticings and wonderings with a partner. Bring the class back together and ask students to share their own noticing or a partner's noticing with the whole group. Students may say (with suggested responses):

  • The shadow is long. (How long is the shadow?) The shadow is longer than the person/the shadow looks twice as long as the person.
  • The shadow is skinny. (How skinny is the shadow?) The shadow is thinner than the person/the person is wider than the shadow.
  • The shadow is dark. (What do you mean by dark?) The shadow doesn't have any color. The shadow is black. You can't really see the color of the grass because the person is blocking the light.
  • The shadow doesn't have details. (Would you say a little bit more about that?) You can't tell what the person is wearing by looking at the shadow. You can't see the person's face in the shadow. You can't see both arms in the shadow.

Say to students, "Many of us noticed the shadow is much longer than the young person in the picture. Does that make you wonder when our shadows are the longest?"

Share the When is my shadow the longest formative assessment probe with your students. Ask students, "Which of these times of day do you think your shadow is the longest?" Ask students to choose the response they agree with and record their thinking using words and/or pictures. Next, ask students to share their thinking with a partner using talk, text, pictures and/or gestures. You might ask a few students to share ideas with the whole class. Welcome all students' ideas and experiences with shadows.

Ask students, "How might we investigate which time of day our shadows are the longest?" Ask students to think independently and record their ideas. Then ask them to share ideas in a small group. As you walk around the room, listen for groups to share ideas about measuring the length of an object's shadow at the times listed on the probe or over the course of a day. Students might suggest measuring their own shadows. When you bring the group back together, begin by calling on those groups whose ideas you want the whole class to hear. Your class may decide collaboratively to

  • Measure the length of a shadow in the early morning, late morning and at noon. I wonder if we could make a few measurements in the afternoon as well.
  • Measure their own shadows How might we measure our own shadows? What will we need to keep the same each time? Stand in the same place each time. Measure from the same place (from the tip of students' shoes to the "top" of their shadows, for example).
  • Measure a different object's shadow like a meter stick

Ask students, "What data do you think we should collect?" Students may only say length of shadow. Ask, "Besides the length of the shadow, what may also be changing from measurement to measurement?" If students are unsure, you might say, "What is causing the shadows? (the sun) How might the sun be changing from morning to afternoon? (the sun will be in different places in the sky/the sun will get higher in the sky)."

Say to students, "We seem to agree we need to measure the length of our shadow and the sun's location in the sky each time we go out." Some methods of recording the sun's location are (1) take a picture of the sun with an agreed-upon reference point (tree or building) in the frame; (2) give students a line drawing with the reference point and ask students to draw the location of the sun relative to the reference point each time; and (3) count how many fists high the sun is above the horizon.

You might choose to create a data table collaboratively. Columns could include time of measurement (consider using a 24-hour clock); length of shadow; position of sun in sky (low, medium, high); and other observations (student will notice the direction of the shadow changes over time when they make their second measurement).

Make sure to remind students not to look directly at the sun. Take students outside to make measurements; ideally students will measure shadow length in the early morning, late morning, noon, early afternoon and late afternoon. You might ask students to use a piece of making tape or draw a chalk line to mark the shadow length before they measure it with a meter stick or tape measure.

NSTA Collection of Resources for Today's Daily Do

NSTA has created a How do shadow lengths change over time? collection of resources to support teachers and families using this task. If you're an NSTA member, you can add this collection to your library by clicking ADD TO MY LIBRARY located near the top of the page (at right in the blue box).

Check Out Previous Daily Dos from NSTA

The NSTA Daily Do is an open educational resource (OER) and can be used by educators and families providing students distance and home science learning. Access the entire collection of NSTA Daily Dos.

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