Sun overhead
Why Are Shadows Short at Noon?
A high Sun casts a stubby shadow. A low Sun stretches it across the ground.
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Step 1 of 5
The Sun crosses the sky through the day.
It rises low in the east, climbs to its highest point around midday, then sinks low in the west. Its height above the horizon changes constantly.
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Step 2 of 5
A shadow is the object's outline, projected along the light.
Light travels straight, so where the light is stopped, the dark shape stretches away in exactly the direction the light was heading.
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Step 3 of 5
Steep light gives a short shadow.
When the Sun is nearly overhead, the shadow is squashed almost directly underneath. At the equator on the right day it can vanish entirely.
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Step 4 of 5
The length follows the angle precisely.
At 45 degrees your shadow is exactly your height. Higher and it shrinks; lower and it stretches, running away to infinity as the Sun touches the horizon.
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Step 5 of 5
Which makes a shadow into a clock.
Because the length and direction change predictably, a stick in the ground tells the time. That is a sundial, and it worked for 4,000 years.
Eratosthenes measured Earth's size in 240 BC using nothing but two sticks, two shadows and some geometry.
The short version
Shadow length tracks the Sun's height — highest at noon, so shortest at noon.
Try it yourself
Put a stick upright outside and mark the shadow tip every hour. The marks trace a smooth curve through the day.
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