As per the International Astronomical Union (IAU), A "planet" is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.”
Our solar system is the best example of planets revolving around a star. The sun is the central star, providing the necessary centripetal force to the eight planets revolving around it. These planets include, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A planet may or may not have a moon - for example, Earth has one moon, Jupiter and Saturn have more than 50 to 60 moons, while Mercury and Venus both have none.
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Moons are natural satellites of planets, orbiting around a primary body. Astronomical studies suggest that moons were big rocks that had been left over during the evolution of the solar system. Some of them started revolving around nearest largest planet or asteroid, while others floated away into space. Ganymede, the moon of Jupiter, is the largest moon of our solar system, while earth’s moon is the fifth largest.
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