Which planet is the closest to the sun in the solar system? 太阳系中哪颗行星离太阳最近？

　　It is Mercury. It is also the smallest planet in the solar system. 水星。它也是太阳系中最小的行星。

　　How small is Mercury? 水星有多小？

　　It is slightly bigger than the moon. 它仅比月球大一点点儿。

　　Even though it is small, Mercury is visible from the Earth. 即使它很小，我们仍能从地球上看到它。

　　In the early morning and at twilight, we can see Mercury. 在清晨和黄昏，我们可以看到水星。

　　From the Earth, Mercury looks bright. 从地球上看，水星很明亮。

　　Then is Mercury the warmest planet? 那么水星是最暖和的行星吗？

　　No, it is not. Mercury takes 59 days to make one rotation. 不是。水星的自转周期是59天。

　　And its orbit is not circular. 它的轨道也不是圆形的，

　　Therefore, some parts of Mercury don't face the sun for a very long time. 所以，水星的一部分很长一段时间内照不到太阳。