Artificial stars (or artisuns) are orbiting sources of illumination that can provide light and heat to a planet or megastructure. These devices are generally powered by fusion or by matter conversion. This is commonly used to provide illumination to the dark side of a Vesperian (tidally-locked) world. They do not emit light in all directions, but instead include a reflecting system that directs the emitted light in a particular direction, like a spotlight. Some artisuns illuminate rotating rings and cylinders and powered by an actual star. The process to make an artificial star is called stellification.