✔ Universe The universe in commonly defined as the totality of everything that exists, including all physical matter and energy, the planets, stars, galaxies and the contents of intergalactic space. The study of universe is known as Cosmology . Cosmology-cosmos (universe) + logos (science) The universe has no limit. ✔ Galaxy A galaxy is a vast system of billions of stars, which also contains a large number of gas clouds (mainly of hydrogen gas) and dust, isolated in space from similar systems. There are about 100 billion galaxies (10 galaxies) in the universe, and each galaxy has, on an average, 100 billion stars (10" stars). So, the total number of stars in the universe is 10 to the power 22 stars. The Milky Way Galaxy is the home of the Ea...
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