Planetary nebulae are the result of red giant stars and their expanding shell of ionized gas remnants. William Herschel named them "planetary" nebula since they resembled the round shape of planets. However, as this picture illustrates planetary nebula can take on a variety of shapes and sizes depending on their distance, and the way in which their core star(s) interact with their expanding gas shells. http://owlmountainobservatory.com