Top ten vacation spots for Moreover, they frequently change their appearance. They can go from being barely visible to being brighter than the full Moon. These strangers may also grow in size to be much larger than the Sun and Moon, and may increase in length to the extent that they stretch across the whole sky. Not only is each comet completely individual, but each apparition of a given comet is unique. What Is a Comet? A comet near the Sun consists of a coma, that is, a dense cloud of dust around a nucleus, and a tail. When far from the Sun, it is nothing more than a bare nucleus undetectable by the naked eye. Nucleus Just as a plum’s lesh surrounds a pit, so a comet coma envelops an inner nucleus. Top ten vacation spots 2016.