The Collaborative International Dictionary
Planetary \Plan"et*a*ry\, a. [Cf. L. planetarius an astrologer, F. plan['e]taire planetary. See Planet.]
Of or pertaining to the planets; as, planetary inhabitants; planetary motions; planetary year.
Consisting of planets; as, a planetary system.
(Astrol.) Under the dominion or influence of a planet. ``Skilled in the planetary hours.''
--Drayton.Caused by planets. ``A planetary plague.''
--Shak.-
Having the nature of a planet; erratic; revolving; wandering. ``Erratical and planetary life.''
--Fuller.Planetary days, the days of the week as shared among the planets known to the ancients, each having its day.
--Hutton.Planetary nebula, a nebula exhibiting a uniform disk, like that of a planet.
Wiktionary
n. (context astronomy English) A nebulosity surrounding a dying star, consisting of material expelled by the star.
WordNet
n. a nebula that was once thought to be a star with its planets but is now thought to be a very hot star surrounded by an expanding envelope of ionized gases that emit a fluorescent glow because of intense radiation from the star
Wikipedia
A planetary nebula, often abbreviated as PN or plural PNe, is a kind of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from old red giant stars late in their lives. The word "nebula" is Latin for mist or cloud and the term "planetary nebula" is a misnomer that originated in the 1780s with astronomer William Herschel because when viewed through his telescope, these objects resemble the rounded shapes of planets. Herschel's name for these objects was popularly adopted and has not been changed. They are a relatively short-lived phenomenon, lasting a few tens of thousands of years, compared to a typical stellar lifetime of several billion years.
A mechanism for formation of most planetary nebulae is thought to be the following: at the end of the star's life, during the red giant phase, the outer layers of the star are expelled by strong stellar winds. After most of the red giant's atmosphere is dissipated, the ultraviolet radiation of the hot luminous core, called a Planetary Nebula Nucleus (PNN), ionizes the outer layers earlier ejected from the star. Absorbed ultraviolet light energises the shell of nebulous gas around the central star, causing it to appear as a brightly coloured planetary nebula.
Planetary nebulae likely play a crucial role in the chemical evolution of the Milky Way by expelling elements to the interstellar medium from stars where those elements were created. Planetary nebulae are also observed in more distant galaxies, yielding useful information about their chemical abundances.
In recent years, Hubble Space Telescope images have revealed many planetary nebulae to have extremely complex and varied morphologies. About one-fifth are roughly spherical, but the majority are not spherically symmetric. The mechanisms which produce such a wide variety of shapes and features are not yet well understood, but binary central stars, stellar winds and magnetic fields may play a role.
Usage examples of "planetary nebula".
The brightest planetary nebula known (a planetary nebula is an expanding cloud usually surrounding an exploding star called a nova) seems to contain particles of magnesium carbonate: Dolomite, the stuff of the European mountains of the same name, expelled by a star into interstellar space.
The butterfly of the bipolar planetary nebula M-two-nine, the Cats Eye, the Hourglass, the central stars of the Cotton Candy Nebula and the Silkworm Nebula, stellar pinwheels, globes within globes.
The remains of the Sun, the exposed solar core at first enveloped in its planetary nebula, will be a small hot star, cooling to space, collapsed to a density unheard of on Earth, more than a ton per teaspoonful.
Voyager had been forced to return to the planetary nebula, the only part of space where they could buy some time in safety.
I also explored the hypothesis that this was simply an ancient planetary nebula whose originating supernova had burned out long ago.
Fassin supposed that it was foolish to expect anything else from a race that was as ancient as the Dwellers claimed to be, who had supposedly explored the galaxy several times over at velocities of only a few per cent of light speed long before the planetary nebula that gave birth to Earth, Jupiter and the Sun had even formed out of the debris of still more antique generations of stars, and who still maintained they felt vaguely restricted not by that absolute limit on the conventional pace of travel but rather by the modest scale of the galaxy that these staggeringly long-ago, almost wilfully leisurely sets of voyages had revealed.
A haze gradually began to define the area of the Okie encampment: a planetary nebula of gas molecules, dust, and condensations of metal and water vapor.
Volya Shadchuk took a One into the heart of a planetary nebula, green-tinged with the radiation from oxygen atoms, and collected fifty thousand dollars.
The solar system became a planetary nebula, a sphere shimmering with fabulous colors, visible across light-years.