About Universe.

Universe

• The study of universe is known as Cosmology.
• 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.
• Galaxy: A galaxy is a vast system of billions of stars, dust and light gases bound by their own gravity. There are 100 billion galaxies in the universe and each galaxy has, on average, 100 billion stars.
• Our galaxy is Milky Way Galaxy (or the Akash Ganga) formed after the Big Bang.
• Andromeda is the nearest galaxy to Milky Way.
• The Big Bang Theory: Big Bang was an explosion of concentrated matter in the universe that occurred 15 billion years ago, leading to the formation of galaxies of stars and other heavenly bodies.
• Stars are the heavenly bodies made up of hot burning gases and they shine by emitting their own light.
• Black Hole: Stars having mass greater than three times that of  the sun, have very high gravitational power, so that not even light can escape from its gravity and hence called black hole.
• Comets: Made up of frozen gases. They move around the Sun in elongated elliptical orbit with the tail always pointing away from the Sun.
• Constellations: The sky is divided into units to enable the astronomers to identify the position of the stars. These units are called constellations. There are 88 known constellations.
• Satellites are the heavenly bodies that revolve around the planets. Moon is the natural satellite of the Earth.