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Some of the young stars are often very massive and so hot that their high energy radiation can excite the gas of the nebula (mostly hydrogen) to shine; such nebula is called emission nebula. If the stars are not hot enough, their light is reflected by the dust and can be seen as white or ... [Planetary Nebula Page]
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www.seds.org/messier/nebula.html
www.seds.org/messier/nebula.html
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Planetary nebula - Wikipedia, the free encyclopedia
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A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas and plasma ejected during the asymptotic giant branch (AGB) phase of certain types of stars late in t...
en.wikipedia.org/wiki/Planetary_nebula
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General information and photos. ... A planetary nebula forms when a star can no longer support itself by fusion reactions in its center. The gravity from the material in the outer part of the star takes its inevitable toll on the structure of the star, and forces the inner parts to condense and heat up.
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www.noao.edu/jacoby/pn_gallery.html
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Planetary nebulae form in the late stages of life of some stars when outer layers of gas that have been shed off glow with energy from the central star. The "planetary" designation refers to their appearance in small telescopes and they are not otherwise related to planets. ... ; Soap Bubble Nebula...
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www.noao.edu/image_gallery/planetary_nebulae.html
www.noao.edu/image_gallery/planetary_nebulae.html
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The formation of a planetary nebula begins when a star has evolved to become a Mira star, a pulsating red giant that sheds matter in the form of a strong stellar wind. At this stage, the star has an inactive carbon core that is surrounded by a helium-burning shell.
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www.daviddarling.info/encyclopedia/P/planneb.html
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planetary nebula: Definition and Pronunciation ... planetary nebula (Thesaurus) ... planetary nebula (Encyclopedia)
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www.factmonster.com/ipd/A0591232.html
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APOD: 2003 June 14 - The Planetary Nebula Show ; Explanation: What do the Owl, the Cat's Eye, the Ghost of Jupiter, and Saturn have in common? They're all planetary nebulae of course, glowing gaseous shrouds shed by dying sun-like stars as they run out of nuclear fuel.
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antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html
antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html
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The Hubble Space Telescope captured this image of a planetary nebula. The lithograph includes a space science lesson plan on the death of a star. ... Then they shed their outer layers and become planetary nebulae. The image of NGC 2440, a planetary nebula, is on the first page of the lithograph. Background information about...
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www.nasa.gov/audience/foreducators/topnav/materials/lis...
www.nasa.gov/audience/foreducators/topnav/materials/listbytype/Planetary_Nebula_NGC_2440.html
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