The Earth as a magnet
Imagine it is a cloudy day and you are out in the countryside. You are lost but you have a map. You climb up a hill and gaze at the woods and fields around you and see a lane winding away below you into the distance. You study your map and see woods and lanes but they do not match your view. On the side of the map is an arrow. It shows the direction of north. You say that this is no help but then a friend takes a compass out of her pocket.

"Will this help?" she asks.

"You bet it will!" you reply.

You open the compass and lay it on a flat rock. Inside the compass is a needle. It wobbles about and is free to turn to the left or the right. Below the needle is a card showing the directions of north, south, east and west. You let the needle settle. At first, it turns to the left, then the right, then a little more to the left and then stops. The needle is shaped like an arrow. You look where the arrow is pointing.

"That", you say, "is north. I can use the map now."

You turn the map so that the arrow faces north. You look out across the view. Suddenly you see how the lane and the woods match up with the map.

"If we go down this lane then turn right, we will reach our camp in half an hour," you tell your friend.

You pack up your map and compass and set off. The compass has helped you find your way.

What happened to the compass to make it point north? The answer begins at a place a long way beneath your feet. In fact it is just over six thousand kilometres beneath your feet ? at the centre of the Earth.

The Earth is a rocky planet but at its centre is a huge ball of solid iron and nickel. It is nearly three thousand kilometres across. Around the ball is a liquid over two thousand kilometres deep. It is made from molten iron and nickel. Above the liquid, the Earth is made of rocky materials. The Earth turns round completely once every day. Inside the Earth the huge metal ball turns round at a different speed from the rest of the Earth. It is through this difference in the way the solid iron and nickel spin, that makes the Earth behave as if it has a huge bar magnet in it.

The Earth spins on a part called the axis. This is a line which runs up the centre of the Earth. At the top of the Earth the axis meets the surface at a place called the North Pole. On the underside of the Earth the axis meets the surface at a place called the South Pole. If we think of the Earth as having a huge bar magnet in it, one end points to a place near the North Pole and the other end points to a place near the South Pole. The place near the North Pole is called the North Magnetic Pole and the place near the South Pole is called the South Magnetic Pole.

The force of the magnet from inside the Earth passes through the rock and out into the air. It spreads out in all directions above the two magnetic poles and streams over the surface of the Earth between them. When you used the compass you were using this force to help you. The compass needle is a magnet. It is loosely fastened inside the compass so that it can be pushed and pulled by the Earth's magnetic force. This was what was happening as the compass turned to the left and right. Eventually it settles down with one end pointing to the North Magnetic Pole and the other end pointing to the South Magnetic Pole.

The end of the compass which pointed towards the North Magnetic Pole contains a place where its magnetic power is strong. This place is called the north-seeking pole or simply the north pole. The end of the compass, which points towards the South Magnetic Pole, is called the south-seeking pole or simply the south pole. As the North Pole and the North Magnetic Pole are quite close together, when you look north you are looking really towards both poles and can simply say that the needle points north. In a similar way you can say that the needle also point south.

Do you know that you can find the north and south by using a bar magnet? Just float it in a bowl of water or hang it from a thread and the power of the Earth's magnetic forces will make it point north and south.

In the story it was a cloudy day. Could a sunny day have helped to find your way?
Yes, it would if you had a watch. The Earth is divided into two half spheres called hemispheres. The top half sphere is called the Northern Hemisphere and the bottom half sphere is called the Southern Hemisphere. If you live in the Northern Hemisphere like the people in the United Kingdom, United States or Japan, the Sun is in a south direction at midday. This means that if you turn your back on it, you are looking north. If you live in the Southern Hemisphere like the people in Australia, South Africa and South America, the Sun is in a north direction at midday. This means that if you turn your back on it, you are looking south. You can use the Sun to help you find north and south if the sky is clear and you are without a compass. If you have a compass it is always best to use it.


What would happen if you brought a magnet near a compass needle?
It would make the needle turn. If you brought the north pole of the magnet near the north pole of the compass needle, the needle would turn away. The reason for this is that similar poles repel each other. A similar repulsion would occur if you brought the south pole of a magnet near the south pole of the compass needle. These actions would occur because similar poles repel each other.

If you brought the north pole of the magnet near a south pole of the compass needle, the south pole of the compass needle would swing towards the magnet. A similar movement would occur if the south pole of the magnet was brought near the north pole of the compass needle. These movements would occur because different or unlike poles attract each other.

When you have a compass needle pointing north and south what do you do with the card below it?
You move the card so that the north and south markings on the card lie under the north pole and south pole of the compass needle. This helps you to see the directions west and east.

How far does the Earth's magnetism reach into space?
Sixty thousand kilometres.

Is the power of the Earth's magnetism in space the same as on the surface?
No. It is much weaker. The magnetic power of any magnet gets weaker as you move away from it. Just put a paper clip on the end of a magnet and then pull it off. You will find that there is a place, perhaps only a couple of centimetres away, where the magnet's force is too weak to pull the paperclip towards it.

Does the Earth's magnetism affect anything in space?
Yes, it does. Billions of tiny particles of matter are streaming out of the Sun in all directions.

When some of them reach the Earth, the Earth's'magnetism pulls them into the atmosphere above the north and south poles. As the particles streak into the sky they rub against the air. This makes them so hot that they glow. The light from these particles is called the aurora borealis in the Northern Hemisphere and the aurora australis in the Southern Hemisphere.