<human>:  What's the difference between a star and a planet?
<bot>: The main difference between a star and a planet is that a star is a large, self-luminous celestial body mainly composed of ionized gases whereas a planet is a much smaller, non-luminous celestial body orbiting around a star. Stars have their own light source whereas planets are illuminated by the light of their parent star. Additionally, stars have much higher masses than planets.