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Topic: Planetary nebula

	planetary nebula
		Planetary nebulae have nothing to do with planets other than their name, which was coined by William Herschel, in the 1780s, because their appearance suggested to him the greenish disk of Uranus.
		The first planetary nebulae to be discovered, and the only ones to be recorded in the Messier Catalogue are the Dumbbell Nebula (M27) in 1764, the Ring Nebula (M57) in 1779, the Little Dumbbell Nebula (M76) in 1780, and the Owl Nebula (M97) in 1781.
		Infant planetary nebulae sometimes show evidence of a bipolar flow, as in the case of the Butterfly Nebula or Ant Nebula.
	www.daviddarling.info /encyclopedia/P/planneb.html (898 words)

	Planetary nebula - Wikipedia, the free encyclopedia
		Planetary nebulae are generally faint objects, and none are visible to the naked eye.
		The nature of planetary nebulae was unknown until the first spectroscopic observations were made in the mid-19th century.
		Planetary nebulae are the end stage of stellar evolution for most stars.
	en.wikipedia.org /wiki/Planetary_nebula (2535 words)

	Stellar Evolution and Death -- Planetary Nebula Formation (Site not responding. Last check: 2007-11-04)
		The envelope material ejected by the star forms an expanding shell of gas that is known as a planetary nebula.
		Planetary nebulae typically have masses of about two-tenths that of the Sun, although some are considerably more massive.
		Planetary nebulae are illuminated by their central stars and display a variety of often beautiful structures.
	observe.arc.nasa.gov /nasa/space/stellardeath/stellardeath_2a.html (385 words)

	Planetary Nebulae (Site not responding. Last check: 2007-11-04)
		Well, because the lifetimes of planetary nebulae are so short, they live for only 50,000 or so years (which is less than 0.001 % of the Sun's lifetime), the chances of seeing this phase of stellar evolution is very small.
		Planetary nebulae are characterized by a shell of material (of mass roughly 10 to 20 % of a solar mass) moving away from a hot (temperatures of 20,000 to more than 100,000 Kelvins), faint star (in their center) at a speed of 10 to 30 kilometers per second.
		Planetary nebula fade away after 50,000 or so years because the material in the shell becomes too rarified to be seen.
	zebu.uoregon.edu /~imamura/208/feb22/feb22.html (527 words)

	Planetary Nebula Collection (Site not responding. Last check: 2007-11-04)
		A nebula (Latin: mist; pl. nebulae) is an interstellar cloud of dust, gas and plasma.
		According to one theory for the formation of planetary nebulae, the hourglass shape is produced by the expansion of a fast stellar wind within a slowly expanding cloud which is more dense near its equator than near its poles.
		In reality, these nebulae have little or nothing to do with planets, but are instead huge shells of gas ejected by stars as they near the ends of their lifetimes.
	www.home.xtra.co.nz /hosts/inspirationalwritings/Planetary_Nebulas.html (1186 words)

	Planetary Nebula (Site not responding. Last check: 2007-11-04)
		The brighter planetary nebulae that they were able to detect were similar to planets in the size they presented in the eyepiece, yet they were obviously gaseous in nature.
		Planetary nebulae are the remains of old stars similar in size to our Sun.
		The Ring Nebula (M57) - easily visible in even smaller scopes, M57 truly resembles a ring as it is thought we are looking down the barrel of it two expanding cones.
	www.nexstarsite.com /_RAC/articles/PlanetaryNebula.htm (454 words)

	Planetary Nebula Spectrum Gallery: Exercise 1
		According to Kirchhoff's laws, the light produced by a planetary nebula should be an emission spectrum, with spikes of emission at specific wavelengths corresponding to the elements in the gas.
		The central star in a planetary nebula is the exposed core of the original star.
		Conditions in planetary nebulae, as it turns out, are extremely conducive to the production of this kind of emission line, and in fact, most of the emission lines you will see in these spectra are forbidden lines, which are denoted by brackets around the ion designation (i.e.
	oit.williams.edu /nebulae/Exercise1.html (983 words)

	Types of Nebulae
		Reflection nebulae are clouds of dust which are simply reflecting the light of a nearby star or stars.
		Dark nebulae are clouds of dust which are simply blocking the light from whatever is behind.
		Planetary nebulae are shells of gas thrown out by some stars near the end of their lives.
	astro.nineplanets.org /twn/types.html (667 words)

	planetary nebula concept from the Astronomy knowledge base (Site not responding. Last check: 2007-11-04)
		The star is so hot that it makes the planetary nebula glow, which allows astronomers to see it.
		A planetary nebula has nothing to do with a planet, but through a small telescope, it looks like a planet's disk, hence the misleading name.
		During the core contraction that terminates the red-giant stage, the helium-burning shell is ejected at a velocity so high that it becomes separated from the core.
	www.site.uottawa.ca:4321 /astronomy/planetarynebula.html (348 words)

	Nebulae
		Diffuse nebulae are clouds of interstellar matter, namely thin but widespread agglomerations of gas and dust.
		Absorption Nebulae or Dark Nebulae: Absorb light: Their gas component can be seen as absorption spectra in the light of background stars, their dust component by absorbing and reddening background light.
		The first of these classes typically includes clouds of interstellar matter of a mass of several 100 or several 1,000 stars, while the latter is related to one specific star in advanced state of evolution, at or just beyond the end of its nuclear life.
	www.seds.org /messier/nebula.html (731 words)

	Rose City Astronomers: Rosette Gazette August 2002 - Planetary Nebula Observing at TMSP (Site not responding. Last check: 2007-11-04)
		On my observing list were 10 non-Messier Planetary Nebulae, half of which were new to me. Based on the views in my 16" scope I would expect all of these to be worthwhile targets in an 8" scope and most would be fine targets in much smaller scopes.
		Planetary Nebula formation is the most common evolutionary path for stars (up to 8 solar masses).
		This is why planetary nebulae, although the most common evolutionary path for stars, are not as common an object as one would expect.
	www.rca-omsi.org /news/gazette02/august02html/planetary_nebula.htm (734 words)

	Planetary Nebulae
		On November 13, 1790, Herschel found the planetary nebula NGC 1514 (his H IV.69), which has a very bright central star; thus he became convinced that the planetary nebulae were nebulous material (gas or dust) associated with a central star, and not unresolved clusters as he and others had thought previously.
		The planetary nebula has only a short life compared to the time scales in stellar evolution, being visible only a few thousands or 10,000s of years, and then fading out as its matter is spread in the cosmic environment, enriching the interstellar matter with carbon, oxygene, and other elements.
		Planetary nebulae have also been discovered in other galaxies with large telescopes, including the Large and the Small Magellanic Cloud, the Andromeda Galaxy M31, M33, M32, and NGC 6822 as well as other galaxies in the Local Group and beyond.
	www.seds.org /messier/planetar.html (1296 words)

	Planetary Nebulae (Site not responding. Last check: 2007-11-04)
		A planetary nebula can result as a star with mass of less than several times the solar mass ("low mass" star) ejects mass in the red giant stage, near the end of the star's life.
		The star at the center of the nebula is extremely hot, reaching temperatures of 200,000 K, emitting a large amount of the ultraviolet radiation which is necessary for ionization of hydrogen in the expanding gas.
		Famous planetary nebulae include the Helix Nebula (New General Catalogue 7293) in Aquarius, the Ring Nebula (M57) in Lyra, and the Dumbbell Nebula (M27) in Velpecula (near Cygnus).
	fusedweb.pppl.gov /CPEP/Chart_Pages/5.Plasmas/Nebula/Planetary.html (500 words)

	Planetary Nebulae
		The Dumbbell, a nearby planetary nebula residing more than 1,200 light-years away, is the result of an old star that has shed its outer layers in a glowing display of color.
		The detection of these knots in all the nearby planetaries imaged by the Hubble telescope allows astronomers to hypothesize that knots may be a feature common in all planetary nebulae.
		Indeed, because of the nebula's shape and the measured velocity of the gas, in excess of 200 miles per second, astronomers believe that the description as a super-super-sonic jet exhaust is quite apt.
	www.cosmiclight.com /imagegalleries/nebulae.htm (6460 words)

	New Image: Orion Nebula "Masterpiece" - Planetary News \| The Planetary Society
		It was "painted" by hundreds of baby stars on a canvas of gas and dust, with intense ultraviolet light and strong stellar winds as brushes.
		Located nearly 1,500 light-years away from Earth, the Orion nebula is the brightest spot in the sword of the hunter constellation.
		The constellation's nebula is invisible to the unaided eye, but can be resolved with binoculars or small telescopes.
	planetary.org /news/2006/1108_New_Image_Orion_Nebula_Masterpiece.html (413 words)

	Proto Planetary Nebula Hints At Stellar SuperWind
		In the first type of structure -- never before observed in proto-planetary nebulae -- a bright, central star is embedded in a faint, elliptically elongated shell of gas and dust.
		Meixner and her colleagues suggest that the axisymmetry found in proto-planetary nebulae could be created by an equatorially enhanced stellar superwind.
		Meixner presented her team's findings at a special conference on asymmetrical planetary nebulae, held Aug. 3-6 at the Massachusetts Institute of Technology.
	www.spacedaily.com /news/extrasolar-99r.html (473 words)

	PAS Intermediate
		Planetary nebulae are the material ejected from very hot central stars.
		In general, the ease at which a planetary nebula can be found will be determined by its size.
		The planetary nebulae that are of mid-size — 50 to 350 arcminutes — are easy to locate at low power.
	www.astronomical.org /astbook/intplanetary.htm (1071 words)

	NASA - Iridescent Glory Of Nearby Planetary Nebula Showcased
		Because the nebula is nearby, it appears as nearly one-half the diameter of the full moon.
		Fortunately, the Helix Nebula was almost exactly in the opposite direction of the meteor stream, so Hubble used nine orbits to photograph the nebula, while it waited out the storm.
		Planetary nebulae, like the Helix, are sculpted late in a star's life by a torrential gush of gases escaping from the dying star.
	www.nasa.gov /home/hqnews/2003/may/HQ_news_03162.html (658 words)

	Lives and Deaths of Stars
		Planetary nebulae can be distinguished from H II regions by their compact shape and strong emission lines of doubly-ionized oxygen (that give them their green color), doubly-ionized neon, and singly-ionized helium.
		Further explanation of the causes of the sometimes bizarre shapes of the planetary nebula is available at Bruce Balick's homepage.
		Planetary nebulae and H II regions are lit up by the action of ultraviolet light on the gas, while supernova glow from shock-wave heating.
	www.astronomynotes.com /evolutn/s6.htm (1617 words)

	ESA - Space Science - Stingray Nebula (Henize 1357)
		A planetary nebulae forms after an aging, low-mass star swells to become a 'red giant' and blows off some of its outer layers of material.
		While stars typically exist for millions of years, the transition to a visible planetary nebula takes only about 100 years — the blink of an eye compared to a star's lifetime - which is why no younger planetary nebulae have ever been identified.
		Named because its shape resembles a stingray fish, the nebula is one-tenth the size of most planetary nebulae and is 18 000 light-years away in the direction of the southern constellation Ara (the Altar).
	www.esa.int /esaSC/SEMSVOW4QWD_index_0.html (333 words)

	Planetary Nebula Club Introduction
		Planetary Nebulae are perhaps the most interesting and beautiful objects in the heavens.
		There are at least a thousand planetary nebulae visible in amateur size instruments and many marvelous ones are not on our list.
		This guide includes the list of 110 planetary nebulae, choosen for this program, along with a nice introduction to planetary nebulae and hints on observing these majestic objects.
	www.astroleague.org /al/obsclubs/planetarynebula/planetneb1.html (1162 words)

	Zoom Astronomy Glossary: P
		Planetary alignment is when many of the planets in the solar system are roughly in a line.
		A large planetary alignment occured on May 5, 2000, when Mercury, Venus, Earth, Mars, Jupiter, and Saturn will be (very roughly) lined up, with all the planets on the other side of the Earth from us.
		A planetary nebula is a nebula formed from by a shell of gas which was ejected from a certain kind of extremely hot star.
	www.enchantedlearning.com /subjects/astronomy/glossary/indexp.shtml (4166 words)

	APOD Index - Nebulae: Planetary Nebulae
		They're all planetary nebulae of course, glowing gaseous shrouds shed by dying sun-like stars as they run out of nuclear fuel.
		Planetary nebulae in general are not at all related to planets, but instead are created at the end of a sun-like star's life as its outer layers expand into space while the star's core shrinks to become a white dwarf.
		The nebula's main ring structure is about a light-year across and the glow from ionized oxygen, hydrogen, and nitrogen atoms are colored blue, green, and red respectively.
	antwrp.gsfc.nasa.gov /apod/planetary_nebulae.html (503 words)

	Properties of Planetary Nebulae
		A planetary nebula is formed when a red giant star approaches the end of its life span and begins to lose a lot of mass very quickly.
		Planetary nebulae are responsible for a large fraction of the mass returned to the interstellar medium each year.
		Planetary nebulae emit visible light of many different colors, depending upon which atoms are present.
	www.astro.washington.edu /labs/clearinghouse/labs/Proppn/proppn.html (810 words)

	NGC 6781, planetary nebula (Site not responding. Last check: 2007-11-04)
		This fairly inconspicuous planetary nebula is in Aquila and it marks the end of the long life of a sun-like star.
		The nebula we see is the ejected surface of the star expanding into material left from an earlier stage in its decline, when it briefly expanded as a 'red giant'.
		Irregularities in the earlier ejecta, asymmetrical outburst of the central star and motion of the new nebula through the interstellar medium as well as the star's orientation in space all affect the physical form of planetary nebulae, so a detailed interpretation of the outburst is difficult.
	www.aao.gov.au /images/captions/aat110.html (273 words)

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