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曙暮光[Twilight] [2005-11-6]
iamet 发表在 ¤〖天文〗
| | The transition period from day to night (or night to day) when the sky is not completely dark, but the Sun has not yet set (or risen). It is technically defined as the period of time beginning (or ending) when the center of the (refracted) Sun is lower than a given elevation. Civil twilight corresponds to the Sun being 6° below the horizon, nautical twilight to 12°, and astronomical twilight to 18°. |
学好数理化，走遍天下都不怕！ | |
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