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Only the Shadow Knows

Ainsley Adams
OverviewProcedure for teachersStudent Resources and Materials
Grade Level
Time Alloment
 Three 45-minute class periods


Have you ever been followed by your shadow? Or have you ever followed it? Shadows are formed because light travels in straight lines. On cloudy days, it can seem as if there are no shadows at all. Yet on a clear day, if you stand with your back to the sun, you are sure to see your shadow. Shadows are formed when an opaque object or material is placed in the path of rays of light. The opaque material does not let the light pass through it. The light rays that go past the edges of the material make an outline for the shadow. The center part of the shadow, which gets no light at all, is the darkest part and is called the umbra. The rest of the shadow is lighter because it gets light from some parts of the source of light, and is called the penumbra.

Through the activities presented in the lesson, students will become familiar with the causes for formation of shadows, an understanding that the shape and length of shadows are dependent upon the position and manipulation of the light source. After a close examination of Web sites and video segments, students, through "free play," will create shadows, compare the size and shape of the shadow with the actual object, engage in shadow play theatre, and discover what happens to shadows when there is much light as compared to little light. Students will measure shadows and draw inferences from the data collected, and finally, using trigonometric functions, calculate heights of objects based on the length of the shadow the objects cast.

Learning Activities

Students should be able to:
  • Use a protractor to measure angles
  • Know that a right angle has a measure of 90 degrees
  • Identify the sides of a triangle
  • Read a table of trigonometric functions
  • Divide by decimals
Students will be able to:
  • Determine what a shadow is and how shadows are formed
  • Measure the size and shape of shadows in relationship to the distance a light source is from an object
  • Determine mathematically the height of an object based on the length of the shadow the object casts


National Standard Education Content Standard 5-8: Science as Inquiry

Design and Conduct a Scientific Investigation
Students should develop general abilities, such as systematic observation, making accurate measurement, and identifying and controlling variables
Develop Descriptions, Explanations, Predictions, and Models Using Evidence
Students base their explanations on what they observe. This allows students to effectively conduct investigations since developing explanations establishes connections between the content of science and the context within which students develop new knowledge.

Use Appropriate Tools and Techniques to Gather, Analyze, and Interpret Data
The use of tools and techniques including mathematics will be guided by the question asked and the investigations students design. Students use computers for the collection, summary, and display of evidence. Students access, gather, store, retrieve, and organize data using hardware and software designed for these purposes.

Standard 3 – Mathematics
Students will understand mathematics and become mathematically confident by communicating and reasoning mathematically, by applying mathematics in real-world settings, and by solving problems through the integrated study of geometry, algebra, data analysis, and trigonometry.

Standard 4 – Science
Students will understand and apply scientific concepts, principles, and theories pertaining to the physical setting and living environment and recognize ideas in science.

Media Components


Reading Rainbow #109: My Shadow

Web sites:

Shape and Space in Geometry
Can you judge an object by its shadow? At this site, students are asked to determine if a shadow can be produced by a particular shape.

The Shadow
This Web site allows students to understand how the shadow of a beach umbrella changes in relation to the sun's position.


Per class:
  • Opaque projector
  • 1 pack copy paper
  • Basketball
  • Overhead transparency of the poem "My Shadow"
Per student:
  • Pencil
  • Ruler
  • Data Shadow Sheet
  • Scissors or hole puncher
Per pair of students:
  • Cardboard
  • Wood
  • Metal cans
  • Stones
  • Potted plants (small)
  • 4 large index cards
  • Flashlights
The following items should be organized in Ziploc bags and placed in a basket:
  • Flathead screw
  • Small funnel
  • Perfume-sized bottle
  • Plastic comb
  • Geometric shape toys (ball, animals, trees, cups)
For teacher:
  • Obtain copy of Shadows and Reflection by Tana Hoban from local library or bookstore.