What Causes A Shadow?

When an opaque or translucent object comes between a light source and a surface, it creates a shadow behind the object where light cannot reach. 

The shadow’s size and shape depend on the object’s position and size.

  • The shadow formed is very large when the light source is close to the object.  
  • The shadow formed is very small when the light source is far from the object.
  • A shadow is darkest closest to the object casting it and becomes lighter as it moves farther away.

Sun’s Effect On Shadows

The length of a shadow changes throughout the day as the sun’s position changes in the sky. As the sun moves in the sky, the shadow moves in the opposite direction.

Shadow length is evidence of the angle of the Sun in the sky.

  • The shadows are longer during sunrise and sunset when the sun is closer to the horizon. 
  • The shadows are shorter during the afternoon when the sun is high up in the sky.
  • Shadows are the longest in the winter. Since the Earth is tilted away from the Sun, the Sun appears lower in the sky.
  • The shadows would be shorter since the Sun is higher in the summer.

Telling Time Using Shadows

A sundial is a device that uses the sun’s position to tell the time of day.

It has a flat plate called the dial face, marked with lines that indicate the hours. 

A triangular blade sticks up from the center of the dial face and casts a shadow onto the dial. 

The shadow moves as the sun moves across the sky, indicating the time. 

Sundials have been used for thousands of years to tell time.

Fun Facts

Here are some interesting facts about shadows:

  • Shadows cast by celestial bodies cause solar and lunar eclipses.
  • Shadow play, also known as shadow puppetry, is an ancient form of storytelling. 
  • We can estimate an object’s height by comparing the length of its shadow to the length of its actual height.
  • When the light comes from an oblique angle, shadows can appear distorted or elongated, sometimes taking on unusual shapes.
  • Shadows can help determine direction and time when hiking or exploring outdoors. 
  • Meteorologists can predict the weather by observing the length and direction of shadows cast by objects such as trees or buildings.


Let’s quickly recap what we learned about the science of shadows:

  • What type of objects create a shadow when they block a light source? Opaque and Translucent Objects
  • Where does a shadow form relative to the object? Behind the Object
  • How does a shadow change based on the sun’s position? Changes Length (Longer or Shorter)
  • In which season does sunlight cast the longest shadows? Winter
  • Which device tells the time based on the sun’s position and the shadows it casts? Sundial
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