One half of its surface— the half which, thanks to the vagaries of orbital mechanics, always faces Earth— is dominated by dark, smooth expanses of ancient, frozen lava known as maria.
其表面的一半---由于轨道力学的变幻莫测,这一半总是面对地球---一直处于黑暗之中, 这片黑暗的地方被称为月海,不仅平坦广阔,而且由老而冻结的火山形成。