The "Planetary Nebulae"
What are they????

Links to more Plantary Nebula information on the web

Links to Kopernik's Planetary Nebula pictures

A Planetary Nebula is a glowing gaseous shell thrown off by a star during the latter stages of its evolution. Eighteenth century astronomer William Herschel named this type of object a 'Planetary Nebula' because the faint green tint and round shape reminded him of his recent discovery, the planet Uranus. (Also note Darquier's 1779 description of M-57 as looking like 'a fading planet'.) Unfortunately, the name stuck, even though these objects have no relationship to the planets!

We now know that they result when moderate to small sized stars reach old age. When stars begin to run short of their hydrogen nuclear fuel, their cores shrink, heat up, and start 'burning' helium. The outer parts of the star greatly expand, forming a red giant star. When even the helium is gone, the core collapses into a White Dwarf star, and the outer parts escape into space, forming an expanding shell. Note that the formation of a Planetary Nebula is a rather gentle event, nothing like the titanic supernovae explosions that mark the passing of heavy stars.

Astronomers are still struggling to understand the true shapes of these gas shells, and how they evolve as they expand. Some Planetary Nebulae have several concentric shells, while some seem to have holes in the shells with jets of material streaming through.

The central stars of Planetary Nebulae are the cores of the preceding red giant stars, and are rapidly evolving into White Dwarf stars. These intrinsically faint stars are very dense and no larger than the earth. A single spoonful of their material weighs as much as a truck. Made mostly of helium, carbon, and heavier elements, they no longer have thermonuclear reactions producing energy. Newly formed White Dwarfs have surface temperatures of at least 85,000 degrees K, and thus radiate mostly ultraviolet light. Over billions of years, they will cool to the frigid background temperature of space.

Although there are several methods to estimate the distance of the Planetary Nebulae, none work very well. Thus astronomers can give only approximate distances that have much less precision than the distances for other deep sky objects.

For more on the "Planetary Nebulae", Check out these links:

To see Kopernik's Planetary Nebula Pictures, Check out these links:

M-27, the Dumbbell Nebula M-57, The Ring Nebula M-76, the Little Dumbbell
M-97, the Owl Nebula   NGC 40, disk
  NGC 246, irregular disk NGC 1501, irregular disk
  NGC 1514, irregular disk  
NGC 2022, disk & ring.   NGC 2371/2, irregular disk, bipolar, polar caps. NGC 2392
aka "The Eskimo Nebula"
NGC 2438, disk & ring NGC 3242
aka "The Ghost of Jupiter"
  NGC 4361, irregular disk NGC 6058, disk & ring
NGC 6309, aka "The Box Nebula" NGC 6369, aka "The Little Ghost" NGC 6765, irregular, bipolar
NGC 6781, disk    NGC 6804, disk & ring
NGC 6818
aka "The Little Gem"
NGC 6826
aka "The Blinking Planetary"
NGC 6842, irregular disk
NGC 6894, ring and disk.  NGC 6905, irregular disk NGC 7008, irregular disk
NGC 7009
aka "The Saturn Nebula"
NGC 7048, irregular disk with trace of ring structure NGC 7293, disk, ring, and central star, aka "The Helix Nebula"
NGC 7662
aka "The Blue Snowball"
Pk 122-4.1, smooth disk
aka Abell 2
Pk 318+41.1, very faint disk
aka Abell 36

George Normandin, KAS

November 1st, 1998
revised Sept. 14th, 2004