My Science School

 

 

The planets travel round the Sun in nearly circular paths. So they are constantly changing direction. A force called ‘gravity’ makes the planets turn. You will have felt the force of the Earth’s gravity – without it you would float up into space! Gravity is a force which pulls. All the planets exert their gravity. The more massive they are, the stronger is their pull of gravity. The Sun is so massive that its gravity is strong enough to keep all the planets turning around it. Without this force, they would each fly off in a straight line.

The Moon also has gravity. Because it is less massive than the Earth, its pull of gravity is weaker – as the astronauts that landed on the Moon found out!

 

 

 

 

 

 

 

Force

Like the planets, this ball will keep moving in a circle as long as it travels fast enough. The force that acts along the string pulls the ball and makes it change direction. Although a different kind of force, its effect can be compared to the gravity exerted by the Sun. if the child let go of the string, there would be no pulling force to keep the ball turning. It would fly away in a straight line.

 

 

 

 

 

 

An astronaut leaps from the Moon’s surface while saluting the US flag.

Occasionally we see ‘wanderers’ in our Solar System. A comet is a ball made of rock and ice. This nucleus is surrounded by a cloud of gas called the ‘coma’. When comets move close enough to the Sun. they reflect the Sun’s light and form a tail of gas and dust.

Comets leave bits of dust from their tails behind in space. Some of this dust enters the Earth’s atmosphere where it burns up. We may then see a shower of bright ‘shooting stars’. The scientific name for a shooting star is a ‘meteor’.

Sometimes lumps of rock or metal from space crash to the Earth. These are ‘meteorites’. A large meteorite may make a crater where it lands. Meteorites probably caused the craters on the surface of the Moon, Mercury and Mars – as well as this one in Arizona.

 

 

 

This meteor crater in Arizona is over 1 kilometre wide and 175 metres deep.

 

 

 

 

 

 

 

Halley’s Comet

Halley’s Comet is a regular visitor to our part of the Solar System. It returns about every 76 years and has been seen throughout the ages. The diagram shows the strange shape of the comet’s orbit – a long oval. The comet is invisible beyond Saturn’s orbit. You can see how the comet’s tail always points away from the Sun.

The planets and stars are far too far away to see clearly, however good your eyesight is. The telescope was invented to help people look at faint, distant objects and see them in more detail. Telescopes collect more light than the human eye. They can also make things look bigger. Stars looked at through a telescope seem to be brighter and closer.

Telescopes use either a lens or a mirror to collect light and focus it. Another lens is used to produce a magnified image. Modern telescopes are housed in giant buildings called ‘observatories’. These are often built at the top of a mountain where there is a clear view of the sky.

 

 

 

 

 

The telescope

This telescope uses one convex lens to collect and focus light, and another to magnify the image. Sliding the outer tube changes the distance between the two lenses. This is important as it allows you to see objects that are near and far away.

 

 

 

 

 

Looking down on a telescope in the observatory at Kitt Peak, Arizona, USA

Watching the Solar System from the Earth is one way of finding out about it. To learn more, people have used rockets to travel into space. There they have been able to look at parts of the Solar System more clearly. But although the first men landed on the Moon in 1969, no one has visited any of the planets. They are too far away and conditions are dangerous for humans.

However, as you have seen space probes – robot controlled unmanned spacecraft – have been sent far into the Solar System. The space probe Voyager 2 has travelled through the Solar System and is now well beyond the orbit of Pluto. As it travels it takes pictures and sends them back to Earth.

 

 

 

Voyager 2

This space probe gas already travelled across millions of kilometres of space, and has collected information on Jupiter, Saturn, Uranus and Neptune. The craft’s onboard computers are reprogrammed during its flight by electronic signals from Earth. The entire vehicle weighs only 815 kilograms. It carries equipment for 11 scientific experiments which are powered by a nuclear generator.

 

 

 

 

 

This is a photograph of the surface of Mars. The surface of Mars – you can see the solar panels of the lander at the bottom of the photo.

 

Life and death of a star

When a star like our Sun first forms it is different from the way we see it today. At first the Sun was a very hot, blue star. As it grew bigger it cooled down and looked white. The Sun will shine as it is for about 10,000 million years. Eventually it will swell and form a ‘Red Giant’. Some of the stars we see are Red Giants. They are cooler than the Sun. But as they are many times bigger, they appear brighter. A Red Giant slowly cools and shrinks. Its outer layers of gas drift away and a small hot star called a ‘White Dwarf’ is left. This slowly cools and becomes a ‘Black Dwarf’.

 

 

 

 

 

Very large stars

Stars much bigger than our Sun also become Red Giants, but they blow up in a huge explosion called a ‘supernova’. They shrink into themselves and form a ‘Black Hole’. Anything nearby gets sucked into a black hole. Even its own light cannot escape!

 

The Sun covers our planet in light and warmth. A mixture of heat and light from the Sun can be used as energy to heat water and make machines work. Energy from the Sun is called solar energy. Solar means to do with the Sun.

The Sun is a blazing star.

This huge burning ball of gas is our nearest star. Even though it is 150 million km away from Earth, the Sun can shine so brightly that you need to shade your eyes from its light. Sunlight can feel hot on your skin. You need to wear sun cream to protect your skin.

 

 

 

 

 

 

 

Energy makes things work. You need energy to throw a ball.

Without energy, nothing works. Everything needs energy. There are many types of energy. The Sun’s energy helps plants and flowers to grow. We eat plants and other foods. The energy from food gives us the energy to throw a ball and run around.

 

 

 

 

The Sun’s heat dries wet clothes.

The Sun is packed with energy. In one hour, the Earth receives more energy from the Sun than the whole world uses in a year. This energy can also be used to generate electricity. We call this electricity solar power.

What happens to the water in a paddling pool on a sunny day? The Sun makes it warm enough to lie in without shivering. This energy from the Sun can heat the water for hot baths and showers. Heat from the Sun can be used to heat houses too.

 

 

 

Sunlight shines through glass in this greenhouse.

Fruits such as tomatoes and exotic plants grow well in a hot greenhouse. The Sun’s light and heat pass through the clear glass windows. When the light and heat are trapped inside the greenhouse, it feels very warm.

 

 

 

 

The Sun can be used to heat up water.

Buildings can be fitted with pipes and plates that collect the Sun’s heat on the roof. These contain a liquid that heats up quickly when the Sun shines on it. The hot liquid is used to heat water. The hot water is sent through pipes to taps, ready for use.

 

 

 

 

Some colours soak up the Sun’s heat better than others.

Paint some paper plate’s different colours, including one black and one white. Put them out in the sunshine for a few hours, and then check which one is hottest, and which one is coolest. Black clothes absorb the Sun’s heat and make you feel even hotter. Solar pipes and plates are black so that they soak up lots of heat.

 

 

The Sun’s energy can be used to make heat and electricity. Special mirrors gather the Sun’s energy. This energy creates heat. The heat is used to turn water into steam. Steam is used to produce electricity.

 

 

 

 

 

 

Mirrors collect sunlight.

Mirrors concentrate sunlight in one place. In a solar power tower, lots of mirrors reflect sunlight onto a special collector. The collector is filled with a liquid. The liquid stays hot for a long time. It is pumped into containers. When power is needed, the liquid flows to a heat exchanger where it heats water and produces steam. The steam turns a turbine that makes electrical energy.

 

 

 

 

 

These curved mirrors turn to follow the Sun.

Power troughs have mirrored surfaces. They turn to follow the Sun. Sunlight heats a liquid-filled pipe in the centre of the troughs. This is sent to a heat exchanger. The steam produced is used to create electricity.

 

 

 

 

 

 

 

Steam from hot water turns a turbine.

Sunlight is used to boil a liquid that heats up quickly. Steam from the boiling liquid powers a turbine. A turbine is like a water-wheel which is powered by steam instead of water. The turbine drives a generator which produces electricity for homes, offices and factories. 

 

 

 

There are other ways that the Sun’s energy is used to make electricity. Have a look at this calculator. At the top, above the numbers, there is a row of solar cells. They use energy directly from the Sun to make the calculator work.

 

 

 

 

 

 

These solar cells turn sunlight into electricity.

The proper name for solar cells is photovoltaic cells, or PV cells for short. Photo means to do with light and voltaic means to do with electricity. Just one PV cell can power a calculator or wristwatch.

 

 

 

 

 

Solar panels are made up of solar cells.

A group of connected solar cells is called a solar panel. Between 10 and 20 solar panels grouped together are called a solar array. Solar panels or arrays work best when they face the sunlight.

 

 

 

 

 

 

 

Solar cells are made from a type of melted sand called silicon.

When sunlight shines on a solar cell, the Sun’s energy makes tiny particles called electrons jump around. When the electrons jump from one layer of silicon to another in the solar cell, electricity is created. The electricity can power a lamp or machine.

 

 

 

 

Solar cells make enough energy to power this torch. Hundreds of solar cells connected together make enough electricity for homes and offices, or to keep small villages supplied with electricity.

 

 

 

 

 

 

Electricity from these solar cells keeps buildings heated and lit.

This housing area in the city of Amersfoort in The Netherlands runs on electricity from solar cells. It is one of the largest solar-powered housing projects in the world. It also includes solar-powered schools anda sports centre.

 

 

 

 

 

This space station uses solar power.

High above the Earth, solar power is used to keep spacecraft working. The solar panels create enough electricity to power the International Space Station, a large spacecraft where astronauts live and work.

 

 

 

 

 

 

Making a solar cell uses up a lot of energy.

Making solar cells is expensive and uses up energy. It takes up to four years to create enough energy from one solar cell to make up for the amount of energy used to create it! In the future, the cost of making solar cells may come down.

 

There are times when we need a lot of electricity, and there are times when we need very little electricity. To make sure we have electricity when we need it, scientists have discovered ways to store solar power.

 

 

 

These lamps store solar power.

A battery is a store of energy. Solar cells can store energy from the Sun in a battery. The battery releases the electricity when it is needed, such as at night. During the day, the solar cells replace the energy that has been used from the battery. This is called recharging.

 

 

 

 

 

 

 

The Sun powers up batteries in this back-pack.

Solar-powered back-packs can provide portable power for a music machine or a computer. During the day, sunlight recharges the batteries for the music machine or computer. Carrying a supply of energy in a back-pack is useful for people living or travelling in remote places.

 

 

 

 

 

 

 

 

Solar power works best in hot and sunny countries.

Places that receive lots of sunshine have the most useful solar power systems. But even in hot countries, the Sun does not shine at night. Solar power can be stored in batteries or it can be used alongside other fuels such as natural gas. 

Solar power is especially useful for people in some remote areas of the world. Here, there may be no power stations and no network of gas or oil pipes to provide fuel for electricity.

 

 

 

This village in Angola, Africa, runs on solar power.

Solar energy is helping this village recover from the effects of war. Solar power provides street lighting and lighting for community buildings, such as the school and medical centre. It provides power for a freshwater pumping system and for hospital fridges that contain important medicines that need to be kept cool.

 

 

 

 

 

Computers can be powered by solar cells.

You probably use computers at school and at home. But in some parts of the world, there is no electrical supply to power computers. Solar-powered computers make it possible for more people there to use computers.

 

 

 

 

 

The Sun’s energy can cook a meal.

The Sun’s rays can be focused to create intense heat for cooking. A mirror or solar box cooker traps the Sun’s heat. The trapped heat cooks the food. Solar cookers mean that people do not have to collect and use up firewood for cooking.

Today we travel across the world in cars, boats and aeroplanes. Most of these vehicles use fuels, such as diesel and petrol. Burning these fuels releases harmful chemicals into the air. Solar power can keep us on the move and it causes less pollution.

 

Cars can fill up on sunshine.

Solar-powered cars don’t use petrol – they use sunshine. Hundreds of solar cells turn sunlight into electricity to power the car’s engine. There are even solar car races. In the American Solar Challenge, cars travel over 3,000 km across the USA, running on sunshine.

 

 

 

 

Sunlight could push spacecraft through space.

In the future, the Sun may be used to power spacecraft through space. A spacecraft would still need rockets to help it leave Earth. Once in space, sunlight would physically push on the sails to propel the craft forwards.

 

 

 

 

The Sun powers this plane.

This solar-powered aircraft is piloted by remote control. It can stay in the air for a long time to study weather patterns. The wings are covered with solar panels, providing the electricity for the aircraft’s motors. A battery provides power so the plane can fly during the night.

 

Roadside telephones, parking metres, flashing road signs and lights in bus shelters can all run on solar power. Houses, flats, offices and schools can all use solar energy to meet their energy needs.

 

 

 

 

 

Some schools are powered by the Sun.

Schools spend about three times more on energy than on books! Using solar power means there could be more money for books. The Star School in Arizona, USA, is completely powered by solar energy. It provides all the school’s power needs, keeps fridges cold and heats up lunches.

 

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