A planetary nebula consists in a glowing (gas and plasma) shell of spherical or ellipsoidal shape that formed around certain growing old stars similar to the Sun (less than 6 times the solar mass). During the red giant phase, they eject the external layers of their atmosphere. The residue of these stars (generally of a mass lower than 1,4 times the solar mass) is dwarf white whose radius is of about 10.000 km (similar to the Earth). The temperature of this dwarf is extremely hot with more than 10.000 °K. It then induces the radiation of nebula gases.

Many planetary nebulas appear to the observer like small discs similar to planets, thus their name.

The classification of planetary nebulas uses the system of Vorontsov-Velyaminov.

Dumbbell Nebula

Other deep sky objects: