有时，面对着地球的是“白天半球”，其它时间则是“夜晚半球”：这就是我们为什么只能阶段性地观察月球。
Sometimes, the side facing the Earth is the day side, and other times it is the night side: this is why we observe moon phases.
近地半球总是面对地球，远地半球总是远离地球，因为月球在绕地球旋转的同时，它也在以同样的速率绕自己的轴自转。
The near side is always facing Earth and the far side is always facing away, because the moon revolves around the Earth at the same rate that it rotates on its own axis.
浩瀚：研究显示，火星北半球的海洋含水量超过地球北半球总水量的10倍
Vast: Mars's northern hemisphere ocean held 10 times more water than all the Earth's, research suggests
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