This is a 4-H Solar Eclipse activity by Cynthia Canan, PhD, State 4-H STEM Specialist, Ohio State University Extension and Sara Newsome, 4-H Alumnus and STEM Student Assistant, The Ohio State University
Reviewed by: Wayne Schlingman, PhD, Director of the Arne Slettebak Planetarium, The Ohio State University, Rachel Chapman, Program Assistant, 4-H Youth Development, Ohio State University Extension-Medina County and Christy Millhouse, Ohio 4-H STEM Educator, 4-H Youth Development, Ohio State University Extension
Topic: Space Science | Estimated time: 30 minutes | For individuals and groups (INTERMEDIATE to ADVANCED level) | PDF for PRINTING
When a total solar eclipse occurs, some places will be completely engulfed in darkness, but some places will still see a bit of the sun peeking out, which is known as a partial eclipse. How can playing with shadows show us why some places experience a total solar eclipse but other places experience only a partial solar eclipse?
NOTE: This activity will work best in a dark room where the only light source is from the activity.
Part 1: Playing with Shadows
Materials
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construction paper (black or dark)
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extended light source, such as a ring light or fluorescent tube light
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point light source (flashlight or phone flashlight)
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skewer
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tape
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white/light wall for shadow play
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chart (one copy)
Be sure to complete this activity in a long space, such as a hallway or gym.
What To Do
- Cut a circle about 2 inches in diameter from the construction paper.
- Attach it to the tip of the skewer with tape.
- Set up the point light source about 3 to 4 feet away from the wall, or have a friend hold it.
- Stand next to the white wall and hold the skewer about an inch away, so that the circle casts a defined shadow on the wall.
- Observe what happens to the shadow as you slowly move the circle further away from the wall and closer to the light source.
- Repeat steps 3, 4, and 5, but replace the point light source with an extended light source.
- Document the differences in the shadows. What are the differences when using a point light source compared to the extended light source at different distances from the wall? Describe what you see in words or by drawing pictures in a copy of the chart.
1 Inch from Wall |
6 Inches from Wall |
12 Inches from Wall |
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Point light source |
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Extended light source |
Differences in shadows between a point light source (left) and an extended light source (right)
Background
Because light rays travel in straight lines, they will keep going in the same direction until they hit something. If that something is an object that can block the light from traveling to the other side, it will create a shadow. A point light source acts as a concentrated lightbulb that sends light from a single point. Because all the light rays are coming from one single direction, an object blocking the light will have a sharp and distinct shadow with clear boundaries even as you move closer to the light source.
An extended or diffused light source, such as a ring light, has light rays that are more spread out, allowing the light rays to come from multiple directions. Shadows from an extended light source can create blurry or softer shadows, especially as you move it closer to the light. This is because only some of the light rays from the extended light source are being blocked. During an eclipse, the moon can create these softer shadows on Earth. This results in a partial eclipse. Therefore, do you think the sun is a point light source or an extended light source?
Part 2: Two-Dimensional Shadows
Materials
- Figure 2 (one copy)
What To Do
To better understand how the different light sources of the sun can create different types of eclipse shadows,
consider a two-dimensional drawing of the sun. The sun is not a single, point-like light source. Instead, it is
a collection of individual light sources over the vast surface of the sun. Figure 1 simplifies this concept by
showing the light cast by only two of the collection of individual light sources.
In Figure 1, you can see the two light sources (the circles on the sun) casting light toward Earth. Different
colors and lines distinguish between the rays coming from the two sources. In Figure 1, light rays from both
sources are reaching the entire surface of Earth.
Figure 2 shows the moon moving between the sun and Earth. As you look at this image, think about what
happens to the light rays when the moon moves in between the sun and Earth.
Use the word bank below to add a label to each box on a copy of Figure 2. Next to number 1, label the type of light rays that will reach each section of Earth’s surface. Each label may be used more than once.
Word Bank: Light Rays
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Next, how do you think the number of light rays correspond to the type of eclipse you will see on Earth?
Use the word bank below to add labels to each box. Next to number 2, label the type of eclipse that will reach
each section of Earth’s surface. Each label may be used more than once.
Word Bank: Type of Eclipse
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Check your work using the Answer Key.
Talking It Over
Write your answers to these questions and talk about them with your project helper or another caring adult.
SHARE Why will some people experience the solar eclipse in totality and others only in partiality?
REFLECT How are the umbra and penumbra different?
GENERALIZE Why do we see shadows?
APPLY What is another way shadows impact how we see the world?
More Challenges
Can you make two different three-dimensional models to demonstrate the two-dimensional
shadows shown in Part 2? Use objects and/or people to create your models.
Background
Because the sun is an extended light source, when the sun, moon, and Earth align, the moon casts different types of shadow on Earth. The umbra is the shadow’s darkest center point, while the penumbra is a type of partial shadow. If you are observing a total eclipse, then you are within the umbra shadow created by the moon. This is because no light rays from the sun can reach you. However, if you see only a partial eclipse, then you are within the penumbra shadow created by the moon. This is because only some, but not all, light rays from the sun are blocked. These shadows appear on Earth at the same time, and what you observe depends on where you are!
During a partial eclipse, the moon casts a penumbra shadow. During a total eclipse, the moon casts an umbra shadow.
Did you know?
An antumbra shadow occurs when the moon moves in front of the sun, but the moon appears to be smaller and unable to completely cover the sun. When the moon is silhouetted within the sun, this creates an annular eclipse, commonly know as the “ring of fire.”
During an annular eclipse, the moon casts an antumbra shadow.
Vocabulary
antumbra. The area from which an object’s body appears entirely within the light source.
prenumbra. An area between a perfect shadow on all sides and the full light. The penumbra is partially illuminated.
umbra. A conical shadow which blocks all light from a given source.
Learn more!
Watch Sun and Shadows by the California Academy of Sciences to learn more about the sun’s path across the sky and its impact on how shadows change throughout the day.
youtube.com/watch?v=oiYZKTpRr8o
SOURCES
“The Solar Eclipse Experience.” American Astronomical Society. eclipse.aas.org/eclipse-america/eclipse-experience
“Umbra, Penumbra, and Antumbra: Why are There 3 Shadows?” timeanddate.com/eclipse/shadows.html
Unless otherwise noted, all images provided by iStockphoto.com by Getty Images.
LEARNING OUTCOMES
Project skill: Understanding the path and intensity of a solar eclipse | Life skill: Problem solving | Educational standard: NGSS MS-ESS1-1. Develop and use a model of the Earth-sun-moon system to describe the cyclic patterns of lunar phases, eclipses of the sun and moon, and seasons. | Success indicator: Analyzes light and shadow to understand the umbra and penumbra
For more solar eclipse activities, visit go.osu.edu/4hsolareclipse.