Science
How are shadows made?
Quick answer
A shadow is a dark area made when an opaque object blocks light. Because light travels in straight lines, it cannot bend round the object, leaving a dark shape behind it.
In one sentence
A shadow is the dark shape that appears behind an object when it blocks light.
Explained
Light travels in straight lines. It can't curve round things. So when an opaque object, one that doesn't let light through, gets in the way, the space behind it gets no light. That dark patch is a shadow.
Think of a garden hose spraying water at a wall. Hold your hand in the spray and there is a dry patch on the wall behind it. Light behaves the same way: your hand catches it, and the wall behind stays dark.
You need three things for a shadow:
- a light source, such as the Sun or a torch
- an object that blocks light
- a surface for the shadow to fall on, such as the ground or a wall
Different materials make different shadows. Opaque things like wood or card make dark, clear shadows. Translucent things like tissue paper make faint shadows. Transparent things like clear glass hardly make any.
Shadows change size and direction:
- Move an object closer to the light and its shadow gets bigger.
- Move it further from the light (closer to the wall) and the shadow gets smaller and sharper.
Outdoors, the Sun seems to move across the sky during the day as Earth spins. In the morning and evening, when the Sun is low, shadows are long. Around midday, when the Sun is highest, shadows are short. People once used this to tell the time with sundials. Midday shadows also change through the year with the seasons: they are shortest in summer.
Examples
- Your shadow stretching long at sunset.
- Shadow puppets on a bedroom wall.
- A tree's shade keeping you cool in summer.
- A sundial's pointer casting a shadow that moves round the dial.
sun
tree
lamp
hand
Common mistakes
- "A shadow is a reflection." A reflection is light bouncing back. A shadow is where light is missing.
- "Shadows show colours and faces." A shadow is just a dark outline. It doesn't show details or the colour of the object.
- "The Sun really moves across the sky." It looks that way because Earth is spinning.
Quick quiz
Shadows
Check what you know with 4 quick questions.
Question 1 of 4
What do you need to make a shadow?
Practise it
Try it
Make shadow puppets with a torch and see how the size changes as you move. Then try more physics activities.
Light and shadow activities
For grown-ups
Related topics
Light
Light is a form of energy that travels in straight lines, very fast. We see things when light from them enters our eyes, either because they make light or because they reflect it.
Seasons
Seasons happen because Earth is tilted. As Earth orbits the Sun over a year, each half of the planet takes turns leaning towards the Sun, getting more direct sunlight and longer days.
The solar system
The solar system is the Sun and everything that orbits it, including eight planets, their moons, dwarf planets such as Pluto, asteroids and comets.
The Moon
The Moon is Earth's natural satellite, a rocky ball about a quarter of Earth's width that orbits us roughly once a month. It shines by reflecting sunlight.
Electric circuits
An electric circuit is a complete loop that electricity flows around. A simple circuit has a battery, wires and a component like a bulb. If the loop is broken, the electricity stops.
Electricity
Electricity is the flow of tiny charged particles called electrons through a material. It powers lights, phones and machines, and it can come from batteries or the mains supply.