When stars like the Sun come to the end of their lives they emit a shell of gas that glows due to ionisation from the remaining core of the star. Planetary nebulae are typically about a light-year in diameter and often look beautiful in images and long exposure photographs. The name was coined by William Herschel who thought their resembled the planets, although they have no connection whatsoever with them.
There are no planetary nebulae visible to the naked eye but the brightest examples can be seen in binoculars and small scopes. These include the Ring Nebula (M57), the Dumbbell Nebula (M27) and the Helix Nebula (NGC 7293).