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Beyond the Solar System

If we were to take a trip in a supersonic jet flying at twice the speed of sound it would take us over 400 years to travel from the Earth to Pluto, at the very edge of the Solar System even if our plane could be made to fly through space.

But if we continued our journey at the same speed it would take us more than 2 million years to reach even the nearest of the stars.

If we look out of our windows on a clear night we will see the stars. They seem like unchanging points of light in the sky but as we watch from hour to hour or from night to night we will see that their positions change. They seem to rise in the East and drift towards the West as the night goes by, just like the Sun.

This is because the Earth is a globe some 12800 km in diameter that is slowly spinning in space. It takes twenty four hours to spin round once and we call this ONE DAY.

The stars are "fixed" in the sky and the Earth spins beneath them. This means that if we look up into the sky tonight the stars will be in roughly the same place that they were last night and will be tomorrow night at the same time.

If you go out at night and look at the sky you are likely to think that you can see a very large number of stars. In fact even on a clear night you only see about three thousand stars at a time, during a whole year you will only see about six thousand.

On any night you will only see some of the stars, the others will be below the horizon, and of course there are millions of stars that are much too faint to see without a telescope.

The stars seem to be grouped together and we call these groups CONSTELLATONS. You will see some of these in the star map in Figure 1.

This map shows you the main groups of stars that you could see during the year. Of course if you look at the night sky you will see a lot more faint stars.

The dotted part of the map is the Milky Way.

You could draw some star patterns on paper and fix them to the walls of your room. Now spin round slowly in front of them. As you spin you look at different patterns of stars but the positions of the stars don't change - they stay where they are - it is you that is moving.

If you look at the sky from night to night you should notice two important things. All the stars appear to circle slowly round the pole star during the night and the position of the constellations also changes from one night to the next.

It's easy to imagine that we are still and that the stars move round us and this is what was thought by most people until the seventeenth century. The Christian Church believed that because Jesus was born on the Earth it must be the centre of the Universe and that everything else must go round it.

However, they were wrong. One simple way of seeing that is to look very carefully at where a star is on one night and then see if it is in exactly the same place 24 hours later - it wont be! In fact the stars rise from the east 4 minutes earlier each night so each star will be a little further to the west at the same time on following nights.

This is because the Earth is moving in a huge orbit round the Sun. It takes a year to travel round once and this movement means that we are looking at the stars from a slightly different place in the orbit each night so their positions seem to move a little. If we wait exactly ONE YEAR then the stars will be in the same position again. However the stars take just about one day to go once round the pole star.

You can see how two of the stars of the Great Bear always point towards the Pole Star. This is a way of finding north because the Pole Star is always north so if you can find it you have found north.

So far our view of the Universe is of the Sun at the centre, the Earth going round it and the stars on a huge globe surrounding everything.


If we watch the sky carefully from night to night to night we will see that some of the stars move relative to the others. These were given the name planets (or wanderers) by the Greeks and in the seventeenth century it was suggested that these planets, like the Earth all go round the Sun. In fact the Earth is one of the nine planets that we know of today, the Sun and its group of nine planets and other smaller objects is called the SOLAR SYSTEM.


© Keith Gibbs