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Th place we live in:
  • The Universe consists of millions of such galaxies.
  • The Galaxy consists of a large collection of stars and celestial bodies held together by gravity.
  • The galaxy that we live in is the Milky Way galaxy, which is spiral in shape.
  • The solar system comprises the Sun at the centre and the celestial bodies such as planets, comets, asteroids, and meteors that revolve around the Sun in a fixed orbit.
  • Sun is a ball of hot gases mainly composed of hydrogen and helium with many other gases.
  • Dakshinayan or winter solstice - Shifting of the Sun towards the south, which starts from \(21\ June\).
  • Uttarayan or summer solstice - Shifting of the Sun towards the north starts from \(22\ December\).
  • From the equator, only on two days of the equinoxes (around \(21\ March\) and \(23\ September\)), the Sun rises in the east.
  • A planet is an astronomical object or a celestial body that orbits a star. Stars twinkle, whereas planets do not twinkle.
Criteria for a planet:
  • It should orbit the Sun or its respective stars.
  • The celestial object should be spherical in shape.
  • It should have a clear area around the orbit.
Solar system:
  • The solar system comprises of Sun and the eight planets.
  • Inner planet / terrestrial planets / rocky planets - The first four planets, Mercury, Venus, Earth, and Mars, are closer to the Sun.
  • Outer planet / Gas giants / Jovian planets - The latter four planets, Jupiter, Saturn, Uranus, and Neptune, are farther away from the Sun.
Basic terms:
  • The planet revolves around the Sun in a definite elliptical path called an orbit.
  • Revolution is the time taken by a planet to revolve around the Sun.
  • Rotation is the time taken by a planet to complete one rotation on its axis.

A satellite is a celestial body revolving around another celestial body. The two types of satellites are,
Natural satellite - Moon
Artificial satellite - Communication satellite