A light-second is a unit of length useful in astronomy, telecommunications and relativistic physics. It is defined as the distance that light travels in free space in one second, and is equal to exactly 299,792,458?metres.
双语例句
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Uranus looms well over 2.5 light-hours away from Earth tonight. In contrast, the moon - our nearest celestial neighbor - resides only 1.3 light-seconds away.
This evening, the moon is about 1.3 light-seconds from Earth, while Jupiter is nearly 36 light-minutes away. Jupiter lies a good 1600 times farther off than the moon.