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planetary nebula |
Also found in: Dictionary/thesaurus, Medical, Acronyms, Wikipedia, Hutchinson | 0.04 sec. |
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planetary nebula: see nebula nebula (nĕb`y  lə) [Lat...... Click the link for more information. . planetary nebulaAny of a class of bright nebulae that may somewhat resemble planets when viewed through a small telescope but are, in fact, expanding shells of luminous gas around dying stars. A planetary nebula is the outer envelope shed by a red giant star not massive enough to become a supernova. Instead, the star's intensely hot core becomes exposed (see white dwarf star) and ionizes the surrounding shell of gas, which is expanding at tens of miles per second. How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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6 After a billion years, the red giant ejects its outer layer as a planetary nebula, leaving a collapsed core at the center. The delicate structure within a planetary nebula appears within concentric rings of red, yellow and blue. In less than 1,000 years, the exposed core will heat up and ultraviolet radiation will stream out, setting the ejected gas aglow and creating a striking tableau known as a planetary nebula. |
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planetary nebula
