What is the difference between a star, sun, planet and a moon?
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First of all, a star is a luminous celestial body, just like our sun. So our sun is a star.
The definition of a planet has changed alot but the most recent difinition of a planet is a celestial body orbiting a sun with enough mass to dominate its orbit. If its mass is great enough for fusion to occur, it's a star. So the biggest difference between a star and a planet is that a sun is massive enough for fusion.
A moon is a celestial body orbiting a planet or asteroide. There is no clear definition of how big it has to be bur if you can spot it, you can call it a moon.