It can appear in an amazing variety of forms and colors. Much of the interstellar medium is invisible; in fact, it will block the view of distant astronomical objects. However, through various physical processes, the interstellar medium can collect in special configurations and produce beautiful nebulae with remarkable shapes and sizes. The names of some of these nebulae reveal some of their charm: the Rosette, the Cat’s Eye, the Hourglass, the Clownface, and the Veil.