Space Astronomy Laboratory
ASTRO - 2
WUPPE PROGRAM CLASS 4.1
PLANTEARY NEBULAE
Planetary nebulae are small, luminous nebulae, more or less circular in form. They are called "planetary" because under low magnification, they resemble the disks of planets. They usually contain hot, central stars, apparently evolving to the white-dwarf stage. The gaseous shell that is the nebula is thought to have been ejected from the central star.