Why Shadows Change Size
Shadows grow or shrink because the angle of the light source relative to the object changes, which changes how far the blocked light stretches across the ground.
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Why do shadows change size during the day?
A morning your shadow stretches across the lawn, but at noon your feet block almost no light at all.
It feels like the Sun moved, but the Sun is far away. So what really changes a shadow's length and size?
A side-by-side comparison of shadows cast by the same object at different sun heights, plus a light-and-block simulator that lets you change the light angle.
Shadows change size because the angle between the light source and the object changes — when light is low, shadows are long and stretched; when light is overhead, shadows are short and compact.
Shadows change because the Sun itself gets bigger or smaller as it moves across the sky.
- Phases of the Moon
- Earth's orbit and seasons
- Sundial gnomon geometry
- Umbra/penumbra detailed physics
- 01Why Does Your Shadow Change Size?slideQuestion
Open with two contrasting scenes: a child with a giant morning shadow and the same child with a tiny noon shadow. Pose the driving question.
- Morning: shadow is very long
- Noon: shadow is very short
- What changes the shadow, and what does not?
- 02What Makes the Shadow Bigger or Smaller?quizPrediction
Ask the learner to commit to one explanation before any evidence is shown.
- Make a single choice between light-angle, sun-distance, object-size, and cloud-cover explanations
- 03Light and Block SimulatorinteractiveEvidence
Let the learner move a lamp from low angle to high angle over a fixed block and watch the shadow stretch, shorten, and shift.
- Move the lamp up and down
- Watch shadow length change
- The block never moves
- 04Same Stick, Three ShadowsslideEvidence
Show a fixed stick casting three shadows: a long one at sunrise, a medium one mid-morning, and a tiny one at noon — with the sun visibly at three different heights.
- Object is identical in all three
- Shadow length changes with sun height
- Sun is far away in all three
- 05It's All About the AngleslideExplanation
Explain with a simple diagram: low-angle light is blocked for a long distance along the ground; high-angle light is blocked for a short distance. Use right-triangle geometry to show why.
- Light rays travel in straight lines
- Low sun = stretched, long shadow
- High sun = short, compact shadow
- 06Does Object Size Matter?interactiveBoundary
Let the learner swap in a taller and a shorter object at the same light angle to show that object size scales the shadow but does not explain why it changes through the day.
- Bigger object = bigger shadow at same angle
- Smaller object = smaller shadow at same angle
- But angle is still what changes during the day
- 07Try It: Lamp, Book, WallinteractiveTransfer
Transfer the idea to a new setup: hold a book near a wall, move a lamp from low to high, and predict the shadow's size before each move.
- Predict low-lamp shadow
- Predict overhead-lamp shadow
- Compare to prediction
- 08Shadows Change Size Because of the Light's AngleslideResolution
Directly answer the driving question. Summarize: object stays the same, Sun stays far away — only the direction of light changes, and that direction is what stretches or shrinks the shadow.
- The Sun's height in the sky sets the angle
- Low angle = long shadow
- High angle = short shadow
- Object size only scales the result
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