| 释义 |
WordReference Random House Unabridged Dictionary of American English © 2024plan′etary neb′ula, [Astron.]- Astronomyan 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.
- so named for its resemblance to the planets Uranus and Neptune 1850–55
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