Chapter 1

The Solar System is made up of the Sun and all of the smaller objects that move around it. Apart from the Sun, the largest members of the Solar System are the eight major planets. Nearest the Sun are four fairly small, rocky planets - Mercury, Venus, Earth and Mars.

Beyond Mars is the asteroid belt – a region populated by millions of rocky objects. These are left-overs from the formation of the planets, 4.5 billion years ago.

On the far side of the asteroid belt are the four gas giants - Jupiter, Saturn, Uranus and Neptune. These planets are much bigger than Earth, but very lightweight for their size. They are mostly made of hydrogen and helium.

Until recently, the farthest known planet was an icy world called Pluto. However, Pluto is dwarfed by Earth’s Moon and many astronomers think it is too small to be called a true planet.

An object named Eris, which is at least as big as Pluto, was discovered very far from the Sun in 2005. More than 1,000 icy worlds such as Eris have been discovered beyond Pluto in recent years. These are called Kuiper Belt Objects. In 2006, the International Astronomical Union decided that Pluto and Eris must be classed as dwarf planets.

Even further out are the comets of the Oort Cloud. These are so far away that they are invisible in even the largest telescopes. Every so often one of these comets is disturbed and heads towards the Sun. It then becomes visible in the night sky.

   Chapter 2 

The Milky Way  

The Milky Way is shaped like a huge whirlpool that rotates once every 200 million years. It is made up of at least 100 billion stars, as well as dust and gas. It is so big that light takes 100 000 years to cross from one side to the other.

The centre of the Galaxy is very hard to see because clouds of gas and dust block our view. Scientists think that it contains a supermassive black hole that swallows anything passing too close.

Outside the main spiral are about 200 ball-shaped clusters of stars. Each 'globular cluster' is very old and contains up to one million stars. The Milky Way belongs to a cluster of at least 40 galaxies. The so-called Local Group has two large spiral galaxies – the Milky Way and Andromeda.

The others are much smaller. They include two galaxies that can be seen with the naked eye from countries south of the equator. The galaxies are called the Magellanic Clouds, after the Portuguese explorer Ferdinand Magellan.

         Chapter 3 
     The Universe

The Universe is everything we can touch, feel, sense, measure or detect. It includes living things, planets, stars, galaxies, dust clouds, light, and even time. Before the birth of the Universe, time, space and matter did not exist. The Universe contains billions of galaxies, each containing millions or billions of stars. The space between the stars and galaxies is largely empty.