| 单词 | planetary nebula |
| 释义 | > as lemmasplanetary nebula planetary nebula n. Astronomy an expanding shell of gaseous material surrounding a star which has ejected it. ΚΠ 1785 W. Herschel in Philos. Trans. (Royal Soc.) 75 266 A very bright, planetary nebula, about half a minute in diameter, but the edges are not very well defined. 1854 D. Brewster More Worlds xi. 173 Planetary nebulae, or such as resemble planets from their discs being round or slightly oval. 1917 Science 25 May 543/2 The nuclear stars of the planetary nebulæ. 1994 Sci. Amer. Oct. 39/2 The last stages of burning are unstable: the star pushes off its outer layers to form a shell of gas called a planetary nebula. < as lemmas |
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