An expanding shell of gas surrounding a star at a late stage of stellar evolution. The name derives from the description given by William Herschel, who thought their circular shapes were reminiscent of the discs of the planets as seen through a small telescope. There is no connection between planets and planetary nebulae. Planetary nebulae are formed as a result of mass loss at the end of evolution of red giant stars up the giant branch. A shell of gas is expeled and the cores of the dying stars ultimately become white dwarfs. Planetary nebulae take a variety of forms -ring shaped, circular, dumbbell-like, or irregular. Notable examples include the Ring Nebula, the Helix Nebula and the Dumbbell Nebula.