Some comets like Comet McNaught glow very brightly in the sky. However, they are not a sun, obviously. They are just large chunks of rock? It can't just be from the sun's reflection? Or is it as the bright ones have an ice coating around them. I know they have large kinetic energy but not enough to radiate at the wavelength of visible light. How do they get into orbit in the first place? Is it usually from a volcanic explosion from one of the planets in our solar system? Or do they usually come from outside our solar system.