My Science School

In the beginning our universe was a mass of white-hot vapours and molten materials whirling about in space. Our world was formed from this. Astronomers believe it took millions of years for the cloud to cool, contract and begin to turn into molten rock.

      Modern astronomers think that many millions of years ago there was a huge explosion in space. They do not know exactly what happened. But it is possible that our sun exploded or that a much bigger companion star of the sun became a supernova-that is, it broke up violently. The debris and blazing gases from this explosion were, it is thought, flung far into space.

      For more millions of years our solar system boiled and bubbled. But very slowly, the fiery redness began to cool and condense into the nine planets and many smaller bodies. All these planets now revolve around the sun.

     After further vast periods of time the lava of the earth began to solidify, developing over many millions of years, into the world as we know it today.

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Why are times different in other countries?

Clocks in other countries need to be adjusted so that it gets light and dark at approximately the same time everywhere. Without this adjustment, people might find that dawn was at 10 o’ clock in the evening, for example.

In 1884 time zones were set up around the world, measured from Greenwich in London, England. Every time zone east or west of Greenwich has noon at a different time. Each zone is either one hour ahead or behind of its neighbouring zone – it is one hour earlier to the west of each zone, and one hour later to the east.

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What are the northern lights?

           The northern lights are streaks and sheets of pale, flickering, coloured lights that are sometimes seen in the night sky in far northern regions. Their proper name is the aurora borealis. The same effect also occurs in the far south, where it is known as the aurora Australis.

            Auroras take place between 97 and 1,000 km above the Earth’s surface. They are caused by electrically charged particles from the Sun. These particles strike the Earth’s atmosphere and release energy in the form of light. Auroras are most common when there are many sunspots, which increase the amount of energy released by the Sun.

Picture credit: google

 

Why do we have coloured sunsets?

Coloured sunsets happen when light is scattered by dust and water particles in the air, as the Sun sets. At sunset, the light passes through a much greater thickness of air, because it strikes the atmosphere at a shallow angle. The farther the light has to pass through the air, the more likely it is to be scattered by the dust particles, causing the red colouration.

 

 

 

 

 

 

Why does the Sun rise in the east?

The direction of the Earth’s rotation means that the Sun appears to rise in the east and set in the west. If you imagine that you are standing at the North Pole and looking down on the Earth, it would rotate anti clockwise. In other words, the Earth rotates towards the east, so the Sun first becomes visible from that direction.

 

 

 

 

 

 

 

What is the Earth’s axis?

The Earth’s axis is an imaginary line through the geographic centre of the Earth about which it spins. You can think of the axis as being like a stick pushed through the middle of an orange. The axis is tilted at an angle of 23.5 degree from the vertical, in relation to the Sun. We still do not know the reason for this tilt.

 

 

Why do we have day and night?

As the Earth spins on its axis, the Sun always shines on one side giving us daylight. It is night on the shaded side. As the Earth continues to turn, the shaded side moves into the Sun’s light and the sunlit side turns away from the light. It takes 24 hours for the Earth to make one complete turn on its axis, and our clocks are based on this principle.

In the 1940s, people discovered that the Earth speeds up and slows down a little as it spins, although the reason for these changes is not fully understood. We have now developed atomic clocks that can measure time exactly.

 

 

 

 

Why do we have seasons?

We have seasons because the Earth is tilted on its axis. As the Earth moves around the Sun, the hemisphere tilted towards the Sun receives more sunlight and this is summer time. The days are longer and the weather is warm because of the extra sunlight. The hemisphere tilted away from the Sun receives less sunshine, has shorter days and is cooler – it is winter time. The area near the Equator is always exposed to the Sun’s rays, so it is warm all the year round. This means that there is little difference between the seasons.

What is the Milky Way?

The Milky Way is a huge mass of gas and stars that can be clearly seen as a band of light across the night sky.

            The Earth and everything else in the Solar System is part of the Milky Way. It is known as our Galaxy. It is so huge that light takes nearly 100,000 years to travel from one side to another. Where stars are packed close together the Milky Way is bright, but huge clouds of gas and dust block the light from the other parts of the Galaxy. These clouds prevent astronomers from observing the whole Milky Way.

 

 

 

 

The super supernova

Sometimes a star appears in the sky quite suddenly. This happens when there are pairs of stars rotating together. These are called binaries, and there is usually one large star called a red giant, orbiting with a smaller, hotter star. The nova takes place when gas is drawn from the red giant into the smaller star, where the heat causes a massive explosion and emits huge amounts of light. A supernova takes place when a star collapses as it begins to burn out, then suddenly explodes, producing a huge amount of light energy, and leaving behind a tiny core of neutrons, which is the heaviest substance in the Universe. A pinhead-sized mass of neutrons weighs many thousands of tonnes.

 

Continue reading "The Universe"

 

What was the Big Bang?

The Big Bang is the most popular theory about the creation of the Universe. According to it, the whole Universe was created in a split second in one huge explosion. All matter was squeezed together into a tiny, super-hot, dense ball that was smaller than an atom. The ball gradually expanded as it cooled, then exploded, releasing energy and matter in all directions. We cannot see the Big Bang because it would have happened billions of years ago. But we can see that the Universe is growing steadily bigger. All the galaxies are speeding away from each other as the Universe expands.

 

 

 

 

 

What is the Universe made of?

The Universe is made up almost entirely of hydrogen and helium. These are the two lightest elements. All the rest of the matter in the Universe is very rare. Elements such as silicon, carbon and others are concentrated into clouds, stars and planets. The Universe is held together by four invisible forces. Gravity and electromagnetism are the two familiar forces. The other two kinds are strong and weak nuclear forces. These operate only inside the incredibly tiny nucleus of atoms, holding the tiny particles together.

 

 

 

 

 

 

 

How old is the Universe?

It is possible to calculate the approximate age of the Universe by looking at how fast distant galaxies are moving away from us. However, it is not possible for us to make this calculation accurately. Scientists have estimated that the Universe is between 13,000 and 18,000 million year old.

 

 

Look at the sky on a clear night and you can see thousands of stars. The universe contains countless millions more stars which are too far away to see. Our own part of this vast universe is called the Solar System. If we could travel from one side of the Solar System to the other it would take many years.

Telescopes enable us to see faraway objects such as galaxies.

The Solar System is made up of the Sun, nine planets, several moons (the number changes as more are discovered) and a band of rocks called the Asteroid Belt. The planets and the Asteroid Belt all travel round the Sun. we say they ‘orbit’ the Sun. They each take a certain time to round the Sun. The time is the planet’s ‘year’. As the planets orbit, they themselves spin. They all spin at different speeds. The time they take to spin round once is called a ‘day’. Many of the planets have moons. While the planets orbit the Sun, the moons orbit the planets.

All the planets are different sizes. The Sun is so big compared to the planets that only a tiny part of it fits on the page!

The planets vary greatly in size and all are a very long way from the Sun. The planets closest to the Sun have the shortest years as they do not have as far to travel. The planets with the shortest days are the ones that spin round fastest.

Scientists think that the Sun and planets grew out of a cloud of dust and gas about 4,600 million years ago. Part of this cloud collapsed and shrank and got very hot. This was the beginning of the Sun. The planets formed from the left-over gas and dust that circled the Sun.

Our Sun is a star. Stars form in enormous groups called ‘galaxies’. Our Sun is part of the Milky Way galaxy. Stars are so far apart that we use special units called ‘light years’ to measure distances between them. Light travels faster than anything else in the universe. But light takes about 80,000 years to cross from one side of the Milky Way to the other! We say the Milky Way measures 80,000 light years across.

 

 

 

 

 

Birth of the Solar System

These diagrams show how the Solar System probably began. The Sun formed first at the centre of the cloud. Specks of material bumped into each other and gradually built up into lumps. These grew to form the planets.

Close to the Sun, where it was hottest, rocky planets grew. They had iron at their centres. These are the ‘inner planets’. Further from the Sun, where it was cooler, giant gas planets grew. All the planets moved around the Sun.

 

 

 

 

 

 

This spiral galaxy at the top of the photo is a similar shape to our own galaxy.

 

The Sun keeps the planets in their orbits. Like other stars, the Sun emits radiation in the form of heat, part of which is visible as light. Energy from the Sun is essential for life on Earth.

The Sun is huge. A hollow ball the size of the Sun could hold about a million Earths! It is also very hot. The ‘surface’ of the Sun reaches about 6,000 degree Celsius. The centre of the Sun is about 13 million degrees centigrade!

The Sun is made of the gases hydrogen and helium. At its centre, hydrogen is constantly being turned into helium. This is a nuclear reaction which releases huge amounts of energy. This energy travels to the surface of the Sun and then into space as radiation.

 

 

 

 

 

 

 

 

The surface of the Sun is called the ‘photosphere’. Here there are often dark patches called ‘sunspots’. These are areas of gas that are cooler than the rest of the surface. Although we call them spots, they are many times larger than the Earth. Giant jets of gas shoot out from the Sun. They are called ‘flares’. Sometimes arches of gas loop across the surface. These are known as ‘prominences’.

 

 

 

 

 

 

 

 

 

This picture of the Sun shows a giant loop prominence.

The inner planets – Mercury, Venus, Earth and Mars – are all made of rock. They are quite small compared with some of the other planets. Mercury is closest to the Sun. It is extremely hot during the day but the temperature falls to -175 degree C at night. Mercury is only a little bigger than our Moon.

Although Venus is further from the Sun than Mercury, it is the hottest planet in the Solar System. Venus spins in the opposite direction to all the other planets. It also spins so slowly that its ‘day’ is longer than its ‘year’!

Earth has water, oxygen and moderate temperatures. Because of this it can support life. Mars is about half the diameter of Earth. Temperatures here are never above zero degree C and the only water is ice at the frozen poles.

 

 

 

Venus

On the surface of Venus, below, there are deep cracks and dead volcanoes. The atmosphere is thick carbon dioxide gas and the planet is surrounded by clouds of sulphuric acid.

 

 

 

 

 

 

Mercury

Like the Moon, the surface of Mercury is pitted with crates and covered in dust and stones. There is no air or water. It is bathed in dangerous radiation from the Sun.

 

 

 

 

 

 

 

 

Earth

About three-quarters of the Earth’s surface is covered by water. The atmosphere contains the gases oxygen, nitrogen and a small amount of carbon dioxide.

 

 

 

 

 

 

 

 

Mars

Mars is made of red rocks. It has craters and dead volcanoes on its surface. The atmosphere is dusty and made of carbon dioxide. There are strong winds which blow up dust storms.

 

 

Jupiter and Saturn are the two largest and fastest spinning planets in the Solar System. They are both made mostly of the gases hydrogen and helium. Jupiter is the largest. It weighs two and a half times as much as all the other planets put together. Its outer layer of gas clouds is about 1,000 km thick. Fierce winds blow these clouds and huge streaks of lightning flash between them. Below the cloud layer the gases get denser and denser until they become liquid.

Saturn is made of less dense gases. It could even float on water! The planet looks beautiful as it is surrounded by rings. The rings aren’t solid. They are probably made of pieces of rock and ice which orbit the planet.

 

 

 

 

 

 

Here we see Jupiter with two of its moons. It has at least 39 moons in total.

 

 

 

 

 

 

 

This picture is made up of photographs of Saturn and several of its moons.

Uranus, Neptune and Pluto are the planets furthest from the Sun. they get very little of the Sun’s radiation so they are all dark and cold places. Uranus and Neptune are large planets made of gas. They look greeny-blue because they contain a gas called methane. Uranus is circled by nine rings, which are smaller than the rings around Saturn. The rings seem to be made of rocks and ice.

Pluto is the greatest mystery of all. It was only discovered in 1930 and is even smaller than our Moon. It is probably made of rock and covered in ice. Pluto is usually the outermost planet. But sometimes its orbit crosses Neptune’s for a period of 20 years, and then Neptune is the outermost planet. This last happened in 1979.

 

 

 

 

 

 

 

This artwork shows the Voyager 2 space probe as it passes Neptune’s North Pole.

 

 

 

 

 

Continue reading "THE OUTER PLANETS"

A moon is a ball of rock that orbits a planet. Mercury and Venus are the only planets that do not have moons. Jupiter and Saturn each have at least 16 moons. Our Moon is our closest neighbour in space. Moons may be lumps of material that were left over when the planets formed. Like planets, moons can only be seen when they are lit up by the Sun.

We know more about our own Moon than any other member of the Solar System, apart from the Earth. Astronauts have even landed on the Moon. The Moon is a bare, dead place where nothing lives or grows. Its surface has hills and mountains as well as flat plains and deep craters. There is no water or air on the Moon and it is covered with a layer of fine dust. From the Moon, the sky always looks black and the Earth seems to change shape and go through phases.

 

 

 

 

Phases of the Moon

Our Moon takes  days to orbit the Earth. During this time it seems to change shape. This is because only the side of the Moon that faces the Sun is lit up. And as the Moon orbits the Earth we see different amounts of this lit-up side.

When the Moon is between the Sun and the Earth we cannot see it. This is called a ‘New Moon’. A ‘Full moon’ is when the Earth is between the Sun and the Moon. The diagram shows phases of the Moon seen in the Northern Hemisphere.

 

 

 

 

 

 

Seen from the Moon, (foreground), the Earth appears to change shape.

 

 

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.