an expanding shell of thin ionized gas that is ejected from and surrounds a hot, dying star of about the same mass as the sun; the gas absorbs ultraviolet radiation from the central star and reemits it as visible light by the process of fluorescence.
Empathy vs. Sympathy: Which Word To Use And WhenThe terms empathy and sympathy are often confused and with good reason. Both of the words deal with the relationship a person has to the feelings and experiences of another person. So, let's explore the differences between these terms and how they are most commonly used.
The Most Surprisingly Serendipitous Words Of The DayIn Part II of our lexical stroll down memory lane (see Part I (1999–2008) here), we will be examining word selections from 2009–2018, unearthing serendipitous synchronicities and offering perspicacious perspectives into notable events and trends of the last decade.
- planet zog,
- planetary precession,
- planetesimal hypothesis,
Origin of planetary nebula
First recorded in 1850–55; so named for its resemblance to the planets Uranus and Neptune
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
an expanding shell of gas surrounding a dying star, formed from matter ejected from the star's outer layers; the gas is ionized by the remaining hot stellar core, emitting light in the process
Word Origin for planetary nebula
C18: named from its (occasional) resemblance to a planetary disc
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
[ plăn′ĭ-tĕr′ē ]
A nebula consisting of a rapidly expanding shell of glowing gas, mostly hydrogen, ejected from a red giant upon its collapse into a white dwarf. Ultraviolet radiation from the hot, luminous white dwarf ionizes the expanding gas and causes it to glow. The nebula disappears once the cooling dwarf can no longer ionize it, and its material eventually returns to the interstellar medium. See more at white dwarf.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.