Shadows
Represent data in graphical displays to reveal patterns of daily changes in shadow length and direction, day and night cycles, and seasonal star patterns
What a learner can do afterwards
- Measure and record shadow length and direction at different times of day
- Create a graph showing how shadow length changes throughout the day
- Connect shadow patterns to the sun's apparent position and Earth's rotation
1 · Read
Every day your shadow changes without you touching anything. It stretches out long in the morning and evening, then shrinks small around midday. You already know shadows form when your body blocks sunlight, and that Earth's spin causes day and night. Now you'll learn how to turn what you measure into a graph, a picture that shows the pattern at a glance.
Priya taped a stick to the ground and measured its shadow three times: 8 AM, noon, and 4 PM. Each time she wrote down the length in inches and which way the shadow pointed. When she plotted her numbers on a graph, the dots made a dip in the middle, just like the sun's height in the sky.
When you read a shadow graph, look for the low point. That's when the sun was highest overhead, which is usually near midday, not midnight.
Shadows are longest in the morning and evening and shortest at midday, and graphing your measurements shows that pattern clearly.
More to read
Sun Up, Sun Down
The sun seems to move across the sky every day, and that movement is really Earth spinning. As the sun's position changes, so do shadows.
In the morning, when the sun is low near the horizon, shadows are long. Around noon, when the sun is high overhead, shadows shrink to their shortest. In the evening, as the sun drops low again, shadows stretch out long in the opposite direction from the morning.
A fun way to see this for yourself: stick a pencil upright in a lump of clay outside, then trace the tip of its shadow every hour. By the end of the day you will have a curve that shows exactly how the sun moved across the sky, even though you never looked straight at the sun. If you did this on a different season, your curve would look different too, because the sun's daily path also drifts higher or lower in the sky as the year goes on.
Figuring for Yourself
Long before satellites, a scientist named Eratosthenes figured out the size of the Earth using nothing but a shadow.
He knew that at noon on the first day of summer, the sun sat directly overhead in one Egyptian city, so a stick planted there cast no shadow at all. On that same day, in a city far to the north, a stick's shadow leaned over at an angle. Eratosthenes measured that angle, then measured the distance between the two cities. Because the two places see the sun at different angles at the very same moment, the difference told him how much the Earth curves between them. From that, he calculated the Earth's whole circumference, and he got remarkably close to the real answer.
If you were standing on a planet that did not spin at all, the stars overhead would never rise or set. They would sit frozen in the same spot in the sky all night, every night, because there would be no rotation to sweep them across your view. It's Earth's steady spin that makes stars, and shadows, change position the way they do.
Explore more
2 · Watch
به انگلیسیTake it off screen
Where it sits
Learn first
Optional connections
This opens up
Nothing builds on it yet.
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.