My Science School

Summer - trees burst with thick loads of leaves. Flowers nod in soft, warm breezes. Insects buzz. A blue sky holds a bright, hot sun.

Winter - bare trees stand like bony skeletons against the cold, grey sky. Snow blankets the ground. The sun seems pale and far away.

What causes this difference? Why are some regions usually warm in spring and summer and cold in winter and autumn?

Summer comes to your part of the world when daylight begins early and stretches to almost bedtime or even later. The sunlight is also stronger. Winter comes when not as much of the sun’s light reaches your part of the world.

Daylight hours are few in winter. It may be dark when you wake up and dark when N7ou get home from school. The ground and air cool off.

The difference in the amount of sunlight each season has is caused by the tilt of the planet Earth. While Earth is spinning in space, it is also travelling around the sun. The way the planet tilts as it travels around the sun causes the seasons.

As Earth moves, it spins like a top. It turns around an imaginary line called an axis. We think of this axis like a pole. We call the top end the North Pole and we call the other end the South Pole.

Earth’s axis is tilted, the way a top tilts when it is about to stop. When the North Pole is tilted towards the sun, the northern half of Earth gets more sunlight, and the southern half gets less sunlight. This makes it summer in the north and winter in the south.

Slowly, Earth moves around the sun. Soon the North Pole begins to tilt away from the sun. As this happens, the southern half tilts towards the sun. Then the northern half gets colder. It becomes autumn, then winter, in the north. And the southern half gets warmer. It becomes spring, then summer, in the south.

Picture Credit : Google

Take a walk outdoors early on a sunny morning, and your shadow will be long and to one side. Later in the day, while you’re playing, your shadow becomes short and almost seems to hide. You can probably stretch your leg over your shadow’s head. Later, just before sunset, your shadow friend will be long and to the other side of you. Why does your shadow grow and shrink while you stay exactly the same size?

Your shadow’s size has to do with the sun’s position in the sky. Every day the sun appears to move across the sky. It rises in the east and sets in the west.

When the sun first comes up in the morning, it is very low in the sky. Most of your body blocks some light, so your shadow is very tall. And since the sun always rises in the east, your morning shadow will always be to the west.

As the morning turns to noon, the sun gets higher in the sky, and your shadow becomes shorter. By noon, the sun almost forms a straight line with your body. Your body is blocking very little light from the sun. This makes your shadow very short.

As afternoon passes, the sun’s position continues to move across the sky. The sun moves downwards, and your shadow grows taller again, this time to the east. By the time the sun is ready to set in the evening, it is very low in the sky, and your shadow will once again be very tall. As it gets dark, your shadow disappears.

Picture Credit : Google

The sun does not really disappear at night. It just seems to vanish, because the part of Earth you live on has turned away from it.

Earth is slowly turning all the time. When it is morning, the part of Earth you live on is starting to face the sun. The sun seems low in the sky. As the day goes on, Earth goes on turning, and the sun appears higher in the sky. When your part of the world is directly in line with the sun, it is the time of day we call noon.

Earth continues to turn. Slowly your part of Earth moves away from the sun. That is why it gets darker and the sun seems to go down. Soon your part of Earth is completely away from the sun, and it is night.

Half of Earth is always getting light from the sun. The other half is always dark. As your part of Earth moves away from the sun, the other side is beginning to face the sun. There, the day is just beginning.

Picture Credit : Google

Without the sun, most plants and animals would not survive.

Energy comes up from inside the burning hot centre of the sun. It reaches the sun’s boiling, bubbling surface. Then it shoots out into space as light.

The sun’s light spreads out in all directions through space. It travels at 299,792 kilometres per second. That is about 10 million times faster than most cars move along a motorway.

How do plants make energy from sunlight? Plants are like factories where food is made. Green leaves are made up of millions of tiny cells, like little bags. When sunlight passes into a leaf, those tiny cells catch and hold the sun’s energy. Using the captured sunlight for power, the plant’s cells turn water and a gas from the air into a kind of sugar. The sugar is stored-up energy that is used by the plant.

Much of the sun’s light speeds on into the endless darkness of space. But some heads straight for Earth. It passes through our sky and travels down to us. Here it strikes leaves and blades of grass. Plants use the sun’s energy to make their own food and to grow.

Once a plant has grown, perhaps cattle will eat it. Now the cattle will have the plant’s energy. In time, the bodies of the cattle may be turned into steaks and hamburgers for people to eat. The energy that came from the sun will then go into people’s bodies. People will use this energy to work or play.

Of course, people also eat plants. When that happens, the people get energy straight from the plants.

All living things must take in energy to stay alive. And nearly all energy comes from the sun. So the sun gives us much more than just light and heat. It truly gives us life.

Most scientists think our sun began as a gigantic cloud of gas and dust.

Stars that are growing old often shoot out huge clouds of gases and dust. The gases and dust are made up of all kinds of chemicals. As these gas-and-dust clouds move through space, they pull more and more gases and dust into themselves.

Within each cloud, all the gases and dust come closer and closer together. Over many millions of years, the centre of the cloud is pulled into the shape of a huge ball. The ball’s centre becomes more dense, or packed, than a ball of steel. When gas is squeezed together that much, it becomes very hot. The tiniest parts of some of the gases begin to join together. The ball becomes even hotter and begins to glow.

This is how all new stars seem to form. Most scientists think this is how our own sun began, over 4 ½ billion years ago.

The Sun

Up in the sky, there is a big yellow ball, the sun. It is only one of millions of stars in the universe. But the sun is more important to people than any other star. Without the sun’s heat and light, there could be no life on Earth.

The sun is a star. It is the closest star to Earth. Our word sun comes from the word Sol. Sol was the name of the ancient Roman sun god. From the name Sol comes our word solar, which means “of the sun”. And our solar system includes everything that moves around the sun.

The sun glows because it is extremely hot. The sun’s centre, its core, is a kind of giant furnace in which the temperature is about 15 million °C.

The sun may not look it, but it is huge. At least 333,000 planets the size of Earth could fit into the sun. Why doesn’t the sun look huge to us? The further away something is, the smaller it appears. And the sun is about 150 million kilometres from Earth!

Picture Credit : Google