What is Universe?

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The Universe contains billions of groups of stars known as galaxies. It is believed that the Universe began with a very hot dense explosion called the Big Bang, which took place between 10 and 20 billion years ago. As the Universe expanded, it cooled down and then galaxies, stars and planets were formed. Our galaxy, the Milky Way, is near the outer edge of a huge supercluster of galaxies. The Milky Way has the sun, which is just one of the billions of stars that make the galaxy. The sun forms the centre of the Solar System with nine planets revolving around it. The Earth is one of the nine planets of the Solar System. It has a satellite which is known as Moon. The Universe is continuously expanding and the galaxies are moving away from each other. They will stop moving apart only if the gravitational pull is strong enough to affect their movement. On the other hand, if the galaxies are moving too fast, the gravitational pull will not be able to stop them and the universe will continue to expand.

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