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The Sun

What is the Sun made of?
What are stars made of?
How far away is the Sun?
The Sun looks so small in the sky, so how can it be bigger than the Earth?
Why is the Sun so important to us and all living things on Earth?

How to introduce the topic

What is the Sun? Where does it go at night? Why is it sometimes hot and sometimes cool? Is it weaker in winter?

You should explain to the learners that the Sun is not burning like a fire. A fire needs fuel such as wood or coal, and it needs air. The Sun does not burn like that. You can tell the children that the Sun is burning by nuclear reactions. A gas, called hydrogen, is being squeezed together so hard in the middle of the Sun that it changes into helium. This change of hydrogen to helium gas at its core, makes the Sun very hot. They don't have to understand the words "nuclear reactions" but it allows us to say that the Sun is not burning like a fire.

There are two activities that teach how big the Sun is compared to the Earth. Later this will become important. The learners must understand that the Sun is so massive that its gravitational pull on the planets can keep them in orbit even though they may be as far away as the planet Neptune.

The Sun is the closest star

We call the Sun a star. But you probably thought that you could only see stars at night? And why does the Sun look so much bigger than the other twinkling stars? This is because the Sun is the closest star to us on Earth. The other stars in the sky are much, much further away. Let's find out more about the Sun.

The Sun during different stages of the early morning

The Sun is a huge ball of very hot gas

Our Sun is really a very hot, very big ball of hydrogen gas. The gas is changing into helium gas, all the time, and this change gives off energy which makes the Sun very hot.

The Sun looks like this through a special camera. You must not look at the Sun with just your eyes.

The temperature of the Sun is about 5 500 degrees Celsius on the surface. 5 500 degrees Celsius is hot enough to melt rocks!

The Sun has dark spots on it that we can see with special cameras. The dark spots move on the surface of the Sun as the gas in the Sun is moving all the time. In the photo you can see that the Sun throws out huge streams of hot gas. Can you see this in the bottom left of the picture?

The Sun is very much bigger than the Earth

The Sun may look smaller than the Earth up in the sky. But this is actually because it is very, very far away. The Sun is much bigger than the Earth.

The following activity can be done outside on a pavement where you can draw with the chalk, or else in a sandy area where you can just draw with your finger. The pavement would work better.

How big is the Sun, compared to the Earth?

MATERIALS:

apiece of pavement
a ruler or tape measure
a piece of string longer than 60 cm
a piece of chalk

INSTRUCTIONS:

Draw a circle 1 cm in diameter on the pavement with the piece of chalk. This represents the Earth.
Now, move about 1.5 to 2 metres away from the little Earth and give yourself enough space to draw the Sun.
Draw a circle 108 cm in diameter - this represents the Sun.
To draw a circle with a diameter of108 cm, tie a string around the chalk. Measure 54 cm of string from the chalk and tie a knot there. Hold the knot on the board and move the chalk around the knot to draw a circle.

QUESTIONS:

If the Sun is so much bigger than the Earth, why does it look so small to us?

The Sun looks small because it is so very far away.

The pavement drawing shows the Earth quite close to the Sun. The Earth is actually very far from the Sun. It is 150 million kilometres from the Earth. That is 150 000 000 kilometres.

That is a really long way from the Earth to the Sun. If you went in a car at freeway speed of 120 km/h, you would have to travel for 146 years to reach the Sun. So, the Sun is far away and it is very big and very hot.

If the Sun is so far away, why does it look as big as it does? The Sun is so big that it is difficult for us to understand how big it really is. A model can help us to understand.

Use a model to show how far the Earth is from the Sun.

This is a demonstration - the class need not go outside but can watch through the windows. Alternatively, set this up so that the learners see the learners with the soccer ball and the grain of rice as they enter the classroom.

MATERIALS:

agrain of rice broken in half
a soccer ball
space to move, such as the playground or soccer field

INSTRUCTIONS:

Look at the picture below.
One learner stands in a place where there is a lot of room all around them. This learner holds the soccer ball; this ball represents the Sun.
Another learner stands next to her and holds the half-grain of rice. It represents the Earth.
The learner holding the rice walks away from the learner holding the soccer ball with 24 of the biggest steps he can make. That distance is about 24 metres. The 24 metres represents the distance from the Sun to the Earth.
Now the learner carries the half-grain of rice, walking to walk to his right side. He must always stay 24 metres from the soccer ball. If he does this he will walk in a circle around the soccer ball.

This model shows us that the small Earth moves in a circle around the big Sun.

The soccer ball represents the Sun, and the half-grain of rice represents the Earth.

QUESTIONS:

Stand 24 metres away from the soccer ball. Hold up one finger in front of you, and cover the soccer ball with your nail. Is the soccer ball really as big as your fingernail?

Why does the ball look as big as your nail?

The ball looks smaller because it is so far away.

The Sun is so big that thousands and thousands of Earths can fit inside the Sun. In the picture you can see how their sizes compare.

This is how the size of the Earth compares to the size of the Sun. The Earth is not really this close to the Sun.

The Sun is the closest star to Earth

Our Sun is like the stars we see in the sky at night. Many of those stars are very much bigger than the Sun. They look small because they are so very far away. All the stars are made of gas that is glowing and very hot.

Do you know what a telescope is? It is like a big pair of very strong binoculars which let us view the objects in outer space. Without a telescope we can see about 2 500 stars, but when we use a telescope we can see millions of stars.

Hundreds of thousands of stars seen through the Hubble telescope http://www.nasaimages.org/luna/servlet/detail/NVA2~34~34~80665~136130:Glittering-Metropolis#

Stars that look orange-reddish are not as hot as the Sun, and stars that look blue-white are much hotter than the Sun.

The colours of stars tell us about their temperatures

INSTRUCTIONS:

Look at the photo below and answer the questions that follow.

This is a photograph from NASA of the star cluster of Omega Centauri, showing all the different colourful stars.

QUESTIONS:

Are there more red or blue stars in this picture?

Which of the stars are the hottest?

the blue stars

What colour star is the Sun?

yellow

The Sun is the nearest star to Earth. The second-nearest star is called Proxima Centauri. Light from the Sun takes 8 minutes to reach your eyes, but light from Proxima Centauri takes over 4 years to reach your eyes. The Voyager 1 is a spacecraft that launched from Earth many years ago. It is travelling away from the Sun so fast at a speed of 17 kilometres every second! If Voyager were to travel to Proxima Centauri it would take more than 73 000 years to arrive.

The Sun is important to life on Earth

Without the Sun, life on Earth would not be possible. It would be completely dark and freezing cold. In other words, the Sun provides us with light and heat. Because of this light and heat, many other things become possible.

The Sun sends out heat and light to the Earth. The Earth gets only a small part of the heat and light that the Sun sends out but even that is enough to make us feel uncomfortable on a hot day!

We hang our washing outside to dry. The heat from the Sun helps the clothes to dry. http://www.flickr.com/photos/wmshc_kiwitayro/3520297538/sizes/l/in/photostream/

People used to tell the time using a sundial like this one. http://www.flickr.com/photos/calliope/440681335/sizes/l/in/photostream/

What else can you think of that the Sun helps with on Earth?

We are able to find direction, plants grow using sun light energy, tan in the Sun, warm up.

The Sun provides every living thing on Earth with energy. Do you remember last term in Energy and Change, we learnt how the Sun provides energy for life on Earth?

The Sun's heat and light provide energy throughout the Solar System, but Earth is the only planet we know has is life. Plants and animals survive on Earth because the planet is warm and the atmosphere has air to breathe.

Some people have special heaters on the roofs of their houses. These are called solar water heaters. They use the heat energy from the Sun to heat water for bathing and washing.

Asolar water heater on the roof of a house. The water is in the tank.

Unfortunately the Sun also has harmful effects on Earth, and especially on people if we do not protect ourselves properly.

When there is not enough rain water, drought can occuffects of the drought.http://www.flickr.com/photos/sanderovski/4712725540/

The Sun can damage your skin if you are not careful and do not put suncream on when outside.

The Sun is a star. It is a very, very big ball of gas. It is more than a million times bigger than the Earth!
Earth is 150 million kilometres from the Sun. That is a very long distance.
The Sun is so hot that it gives the Earth all the light and heat we need.
The nearest other star is so far away it looks like a dot made with a pin on paper.

Write out these sentences and complete them. Choose some of the words from the word box to complete the sentences. Write out the whole sentence.

Word box: (You do not need to use all the words)

hydrogen gas

helium gas

plants

light

heat

half a grain of rice

Sun

a soccer ball

the Moon

When we compare the size of the Earth to the size of the _____, the Earth is the size of _____ compared to the size of a soccer ball.