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### Theory:

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:
• 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.
Planet:
• 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.
Satellite:

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