Comets are made up of ice and dust and move through the solar system in orbits. They have been orbiting for thousands of years. When comets orbit closer to the Sun they start to melt and they release dust that looks like a comet's tail or trail. Comets do not come close to our planet, but infact they are millions of miles away. They move very slowly, that is why we can see a comet for several weeks or even months.