My Science School

It is the middle of the day. The sun shines bright in the sky. Suddenly, the sky seems to be growing dark! The sun seems to be disappearing! Soon the sun is nearly as dark as night and there is only a pale, fuzzy ring around it! What has happened?

The moon, which moves around the planet Earth, has passed between Earth and the sun. The sun is much bigger than the moon, but it is so far away from us that the moon seems to cover it up. When the moon is between the sun and Earth, the moon throws a shadow on Earth. The part of Earth covered by the shadow gets dark. This is a total eclipse of the sun, or a total solar eclipse.

Sometimes during an eclipse the moon covers only part of the sun. This is called a partial eclipse.

The sun’s rays can hurt your eyes, so never look directly at the sun - even during an eclipse!

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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.

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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.

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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.

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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!

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Today there are many artificial satellites that revolve round the Earth. Why is all the time, money and effort required to launch them considered worthwhile? The answer is that the satellite performs many useful scientific tasks as it journeys through space.

Artificial satellites can act as spies that seek out military installations and equipment on the Earth below. Another function is communications between distant points of the globe.

They can study the solar radiation and environment of space and this knowledge helps us to understand the forces at work on our own planet and the causes of natural phenomena which effect our living conditions.

Meteorological satellites also exist which record details of weather conditions throughout the world and help in weather forecasting.

 

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During the 1700s after a great deal of hard work astronomers were able to calculate the speed and direction of many stars. By 1805 the astronomer Herschel proved that the Sun itself was subject to the same laws of movement. We now know that the Sun with its whole accompaniment of planets travels through space at the terrifying speed of about 270 kilometres a second together with the whole galaxy in which the solar system lies. The Sun also travels along a path of its own which is directed at a point in the heavens near the star Vega.

Herschel had studied the distant nebulae which astronomers before him believed to be millions of stars. Even the Milky Way was a nebula, but it was much brighter than the others and therefore must be nearer.

Herschel then thought that the Sun, like hundreds of other stars visible from the Earth, was part of huge nebula, separate from all the others and forming a universe of its own:  the galaxy.

During the 1870s the first powerful telescopes found other nebulae outside the galaxy and this proved that Herschel was right. New searches were made in our own century with the installation of the Mount Wilson telescopes in 1905 and the one at Mount Palomar in 1948.Today we can even begin to draw a map of the galaxy. It appears to be shaped like a 100,000 light years (one light year is equal to 10 million kilometres) and contains about 100,000 million stars.

 

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Mercury - Swift Planet

Because it moves quickly around the Sun and circles it faster than all the other planets.

Venus - Morning and Evening Star

The two nicknames given to Venus are because it rises and sets each day, like the Sun. It is visible from Earth, like a star in the sky, in the morning before the Sun rises, and in the evening as soon as the Sun sets.

 

Earth - Blue Planet

Most of the Earth is filled with water, and this makes the planet appear blue from space.

Mars - Red Planet

Mars is nicknamed so because it appears in the sky as an orange-red star. Toray, scientists know that Mars appears so due to the net on the Martian rocks.

Jupiter - Giant Planet / Gas Giant

Jupiter is the largest planet in the solar system. In fact, it is so big that all the other planets in the solar system could fit inside it! It is also known as the Gas Giant because its atmosphere is mostly made up of hydrogen and helium gas just like the Sun.

Saturn - Ringed Planet

Saturn is known so because of its rings. The other gas giants in the solar system, such as Jupiter, Uranus and Neptune also have rings, but only Saturn’s are visible prominently.

Uranus - Sideways Planet / Bulls Eye Planet / Ice Giant

Uranus is four times the size of the Earth ant is the coldest planet in the solar system. Hence, it is called the le Giant. It is known as the Sideways Planet because it rotates on its side. And, as for the nickname Bulls-Eye Planet, it is because Uranus’ rings are vertical, unlike Saturn's which are horizontal. This makes it appear like a bulls-eye on a target.

Neptune - Big Blue Planet / Windy Planet

Neptune looks blue from space, just like Earth, but i many times larger than our planet. Hence it is called the Big Blue Planet. It is sometimes also called the Windy Planet because winds in Neptune can whip clouds of frozen methane at speeds of more than 2.000 km/h!

 

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For thousands of years, people have used the earth’s land, water, and air. Also, people have also polluted the earth with their waste, harmful chemicals, and other poisons.

Now people all over the world are working to protect the earth. They are working to preserve land, stop pollution, save natural resources, and protect endangered wildlife. There are many ways to help the earth. You can help, too.

The Three R’s

How many things did you use today that were made from trees or plastic? How many of those things did you throw away? How many things did you use that required electricity?

Many things that people use are made from trees or plastic. For example, lots of paper and wooden products are made from trees. Many plastics are made from petroleum, coal, and natural gas. And the more we throw away plastic and paper, the more rubbish dumps are needed.

Many things that people use are powered by the earth’s natural resources, too. As we use electricity to run refrigerators and other products, minerals are needed to create that electricity.

Many people are worried that the earth’s resources are being used up and polluted. With these three R’s - reduce, reuse, and recycle - you can help preserve the earth’s resources.

Reduce

• Use fewer paper and plastic products. Use cloth towels instead of paper towels.


• Turn off the lights, radio, and TV when you’re not using them.


• Instead of running water until it’s cold, use ice cubes. Or keep a jug of cold water in the refrigerator.


• To save hot water, take showers instead of baths.


• If you have a dishwasher, don’t use it until you have a full load.


• Ride a bike, or take the bus or train to save on petrol and oil.

Reuse

• Wash out plastic milk bottles, plastic bags, and aluminium foil, and reuse them.


• Repair and reuse toys and other products.


• Save used paper and plastic to make gifts.


• Use both sides of writing paper.


• Sell or donate goods so someone else can reuse them.

Recycle

• Recycle aluminium cans, glass and plastic containers, newspapers, rubber items, and paper. Recycled materials are used to make new products.


• Use recycled paper to write, paint, and draw.

Earth is slowly getting warmer. Most scientists believe that people are helping to cause this change. But how can people cause Earth to warm?

Have you ever seen a greenhouse? The glass walls let in light so plants can grow. Because the walls also hold in heat, a greenhouse becomes very warm.

Earth and its atmosphere act like a greenhouse. Light from the sun passes through the atmosphere and warms Earth. Much of this heat escapes back into space. But such gases in the atmosphere as carbon dioxide act like greenhouse walls. These so-called “greenhouse gases” trap heat in the atmosphere. This is called the greenhouse effect.

Our cars and factories burn fuels that release greenhouse gases. These gases are building up in the in atmosphere. Most scientists believe that the buildup of gases is causing Earth to warm. They fear that our planet will become much warmer in the next 100 years. This problem is called global warming.

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Using the land wisely

Every year, there are more people on the earth using more of the earth’s resources. If people aren’t careful, the resources will be wasted, damaged, or used up.

To make space for the development of houses, roads, pavements, and car parks, people cut down trees and other plants. But careful builders leave areas in their developments where they plant trees to replace the ones they’ve cut down. This allows animals to keep their homes or find new ones.

Also, many governments protect some prairies, wetlands, forests, and other land from development.

Factories and other buildings can send waste chemicals into the air and water. So some countries have laws requiring builders to be careful so that new buildings don’t pollute the air and water.

Workers remove valuable resources from the land. If too much is taken, the supply will be used up. However, in many places, businesses save minerals by using better ways of mining and recycling mineral products. They also substitute more plentiful minerals for scarce ones.

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Pollution is anything that people do those damages the natural environment. For example, if poisonous chemicals are not properly thrown away, they can get into the ground, water, or air.

There are many ways that people pollute the earth. When poisonous chemicals, such as paints and fertilizers, are dumped into rivers and lakes, the plants and animals that use that water may become sick or die.

When waste from people and animals gets into the soil and water, the plants and animals that use that soil and water may become sick.

Some pollution damages the air. Smog is one kind of air pollution. It is created by the action of sunlight on exhaust from cars and factories. Very heavy smog can hurt people. Even countries that work to improve their own air can be polluted by air from a neighboring country.

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The Earth’s natural resources

What if there weren’t an ocean or any lakes, ponds, or rivers? What if there were no plants to eat? What if there were no irons to build things with?

Natural resources include all the things that support life. Sunlight, water, soil, and minerals are all natural resources. There are plenty of some resources, and not so many of others.

Sunlight, for example, cannot be used up. Neither can water. The earth has lots of these natural resources. But some places on the earth have more water, more sunlight, or cleaner water than other places.

Some natural resources can be used more than once. These are called recyclable resources. For example, aluminium can be used to make containers, and the containers can be recycled - used to make something else.

Other natural resources can be used and replaced. Animals can reproduce, so they are replaced with new animals. As trees are used, new trees can be planted.

But some natural resources are replaced so slowly we could run out. For example, people are quickly using up the earth’s supplies of coal, oil, and iron. It would take millions of years for the earth to make more of these resources.

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