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Galaxies

All the stars that we see from the Earth are part of our galaxy. This is an enormous spiral shaped disc shaped like two giant plates held face to face with a diameter of a little over 100 000 light years and made up of some hundred thousand million (1011) stars as well as great clouds of gas. Our Solar System lies about two thirds out from the centre on one of the spiral arms of the galaxy. The galaxy is rotating very slowly about once every 240 million years! Viewed from 'outside' our galaxy would look like the photographs.

There are many other galaxies far out in deep space. Astronomers think that the Universe contains over a billion (1000 million) galaxies! Some are spirals like ours but others are elliptical and some irregular in shape. Each one of these contains around 100 000 million stars.

Galaxies are huge things. Light that we see from the stars on the other side of the galaxy started out on its journey over eighty thousand years ago!

Galaxies are very far away! If we could shrink the whole solar system out to the orbit of Pluto to the size of a grain of sand 1mm across then on the same scale our galaxy would be a disc with a diameter of some 80 m and the nearest galaxy would be about 1500 m away.

Light from the Andromeda galaxy takes over two million years to reach us. The lower picture shows a galaxy seen through the stars in Ursa Major (The Plough). This is called M81 and we are seeing it now due to light that started out from it 11 million years ago!

 
 
 
© Keith Gibbs 2011