| 单词 | nebula |
| 释义 | nebula Originally a fixed, extended, and somewhat fuzzy white haze observed in the sky with a telescope. Many of these objects can now be resolved into clouds of individual stars and have been identified as galaxies. They are still sometimes referred to as extragalactic nebulae . The gaseous nebulae , however, cannot be resolved into individual stars and consist, for the most part, of interstellar dust and gas. In some of these gaseous nebulae the gas atoms have been ionized by ultraviolet radiation from nearby stars and light is emitted as these ions interact with the free electrons in the gas. These are called emission nebulae . In the dark nebulae , there are no nearby stars and these objects are consequently dark; they can only be detected by what they obscure |
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