| 单词 | planetary nebula |
| 释义 | planetary nebula Astron. 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. [1850-55; so named for its resemblance to the planets Uranus and Neptune] |
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