C. Matter and Energy · Energy in Our Lives

The Sun: Earth's Most Important Energy Source

C2.2 A1.2 A1.4 A1.5About 35 minutes

Learning goals

I can explain that the sun is the most important source of energy for Earth.
I can tell how the sun gives us light and warms the air, land and water.
I can explain how the sun helps plants grow.
I can do a test to compare things in the sun and in the shade.

Words to know

sun
The star closest to Earth. It gives Earth light and heat.

source
Where something comes from.

light
A kind of energy that lets us see.

heat
A kind of energy that makes things warmer.

shade
A place where the sunlight is blocked, so it is darker and cooler.

A sunny day in the snow

It is a cold winter morning. By lunchtime, the sun is shining. The snow on the sunny side of the house starts to melt and drip. But the snow in the shade stays frozen.

Why? The sun gives off energy!

Icicles dripping water from a snowy roof edge on a sunny winter day. — The sun's energy is melting the snow on this roof. Look for the water drops falling from the icicles. AI-generated image

The sun is our biggest energy source

The sun is a star. It is very, very far away, but it sends energy all the way to Earth.

The sun is the most important source of energy for Earth. Without it, Earth would be dark and frozen, and nothing could live here.

The sun gives light and warms the air, land and water. It helps plants grow.

What the sun does	Example
💡 gives light	We can see in the daytime without turning on lights.
🌬️ warms the air	Afternoons are usually warmer than early mornings.
🏖️ warms the land	Sand at the beach feels hot on a sunny summer day. A sidewalk feels warm.
🌊 warms the water	A lake is warmer for swimming in August than in May.
🌱 helps plants grow	Plants use sunlight to make their own food.

The sun gives Earth light and heat

The sun and food

Plants use sunlight to make their own food. Animals eat plants. Some animals eat other animals. People eat plants and animals.

So the energy in almost all of our food started with the sun!

Sun safety

Never look straight at the sun, even with sunglasses. It can hurt your eyes.
On sunny days, wear a hat, sunscreen and sunglasses, and drink water.
Snow reflects sunlight too, so you can get a sunburn on a sunny winter day!

Worked example

Let's compare sun and shade

Two ice cubes are put on two plates outside. One plate is in the sun. One is in the shade. Which melts first?

Predict: The sun gives heat, so I think the ice in the sun will melt first.
Keep it fair: Use the same size ice cubes and the same kind of plates. Put them out at the same time.
Observe: Check every 5 minutes. Draw what you see.
Result: The ice cube in the sun melts first.

The sun's energy warms things. The ice in the sun got more heat, so it changed into water faster.

Same ice cubes, same plates, same start time. The cube in the sun gets more heat energy, so it melts into a puddle first.

Worked example

Let's think about the sun and a plant

Grandpa puts his tomato plant in a dark garage for 2 weeks. What happens?

Plants need sunlight to make their food.
In the dark garage, the plant cannot make enough food.
It will turn pale (yellowish) and weak, and it may die.

The plant needs the sun's energy. It should go back into the sunlight.

Just for fun

Funny but true: Sunlight takes about 8 minutes to travel from the sun to Earth. The sunshine on your face left the sun before you finished brushing your teeth!

Hands-on activity

Sun or shade investigation

You need: 2 ice cubes the same size (or 2 small chocolate chips, or 2 crayon pieces on foil), 2 plates, a sunny day, a clock or timer, paper and crayons.

Put one plate in a sunny spot and one in the shade.
Put one ice cube on each plate at the same time.
Predict: Which will melt first?
Check every 5 minutes. Draw what you see.
Then touch (carefully) a sidewalk or a dark car door in the sun and one in the shade. Which feels warmer?

What to look for: The things in the sun should get warmer and melt faster. Talk about it: "The sun gives off heat energy, so..."

Safety: Never look at the sun. Surfaces in the sun can get very hot in summer, so touch them quickly and gently, with a grown-up.

Your turn

What is Earth's most important source of energy?

Name 2 things the sun gives us.

Why do plants need the sun?

Why does snow melt faster in the sun than in the shade?

Name one way to stay safe in the sun.

Would a lake be warmer in June or in August? Why?

More practice: warm-up

Is the sun a star or a planet?

When is it brighter outside: day or night?

Is it cooler in the sun or in the shade?

Does the sun warm the land?

Should you ever look straight at the sun?

More practice: on your own

Your cat likes to nap in a sunny window. Why do you think it picks that spot?

What could happen to Earth if there were no sun?

In the ice cube test, why do we use ice cubes that are the same size?

How does the energy in an apple come from the sun?

In winter, why does a car parked in the sun feel warmer inside than one in the shade?

Challenge

A wet T-shirt is hung outside in the sun, and one is hung in the shade. Which dries first? Why?

A deer eats grass. A wolf eats the deer. Explain how the wolf's energy started with the sun.

Why do you think dark clothes feel warmer in the sunlight than light-coloured clothes?

Check your understanding

Quiz

What is the most important source of energy for Earth?

Which does the sun NOT do?

Where will an ice cube melt fastest?

Why do plants need sunlight?

What is a safe thing to do on a sunny day?

Which is warmed by the sun?

For parents and teachers

Big idea: The sun is Earth's principal source of energy. It gives light, warms the air, land and water, and helps plants grow, and so the energy in our food started with the sun.

Common difficulties:

Thinking the sun only matters in summer. Point out that winter sun melts snow and warms a sunny window too.
Not connecting the sun to food. Trace a food chain at dinner: "The carrot grew in the sunlight, and now you get its energy."
Safety (A1.4): Reinforce never looking at the sun, and wearing sun protection. Supervise touching surfaces that may be hot.

How to help: Do the ice cube test on any sunny day, even in winter (a sunny windowsill works). Notice together which rooms in your home are warmest in the afternoon, and why.