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Our Universe

The earth is one of the planets that revolves around a central star called the sun. The sun is only one amongst the billions and billions of stars that exist in the universe. These stars are not distributed uniformly in space but are found in huge bunches or clusters. Such a cluster of stars held together by gravitational force is called a galaxy. Astronomers estimate that there are about hundred billion (1011) galaxies. Each galaxy, on an average, has about hundred billion stars.
We can see, through telescopes, many faint cloudy patches in addition to stars in the night sky. These are referred to as ‘nebulae’.
Edwin Hubble, in the 1920s, was able to show that many of these nebulae are indeed galaxies similar to our galaxy. Later on he classified these galaxies into three types, namely,
  1. spiral galaxy,
  2. elliptical galaxy and
  3. irregular galaxy.
Today, large telescopes can see about 1011 galaxies.
Our sun and solar system are present in a spiral galaxy called Milky Way galaxy. Our sun is located more than half way (about 26,000 light years) from the centre. Our galaxy contains about 1011 stars and the total mass of all stars in our galaxy is about 3 × 1041 kg.

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