My Science School

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.

 

 

 

 

 

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