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THE UNIVERSE
The Universe is everything that exists include the Sun, The Earth and the other planets, all the other stars in the sky, the Galaxy and all the other Galaxies, and all matter, space and time.
It is very very big! It extends as far as we can observe through telescopes and even beyond what we can see. It is currently thought to be at least 13.8 billion years old, and formed from an explosion called the Big Bang, and has been expanding in size from that ever since.
Our place in the Universe
The Earth is the third planet orbiting around our Sun, and is part of a collection of planets and other bodies in the Solar System. The Solar System orbits around our Galaxy, and the Galaxy forms part of a Local Group of Galaxies. This Local Group is part of the Virgo Supercluster of Galaxies, which is one of many Local Superclusters. These in turn are all part of the Observable Universe, and beyond, into the Unobservable Universe.
Our Galaxy
Our Galaxy contains over 100,000 million stars, is about 100,000 light years wide, and is spiral in shape, with a number of arms spiralling out from the central bulge. Our Solar System is located about two thirds out from the centre, in one of the spiral arms.
On a clear starry night, you can see a faint band of stars running across the sky. This area shows many stars grouped together in a band because when we look at this band, we are looking towards the centre or the arms of our Galaxy. This band is known as the Milky Way. There are gaps seen in this band, and are caused by dark dust that lie in the spiral arms and obscure the light from the stars behind them.
All the stars we see in the night sky are all part of our Galaxy. Some of the objects we can see as fuzzy patches are other Galaxies. Our Galaxy also has two companion galaxies known as the Large and Small Magellanic Clouds. These are not spiral in shape; rather they are irregular elliptical galaxies.
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