在高一物理课本的阅读材料“月相”一文中提到:从地球上看,月亮从圆到缺,又从缺到圆,这是一种周期性变化,周期为29.5天.有同学提出疑问:“我们在前面讲万有引力时,不是说月球绕地球运行的周期为27.3天吗?怎么这里却是29.5天呢?”要说清这个问题还得从月球绕地球运动和地球绕太阳运动谈起. In the article “The Phase of the Moon” in the reading materials of the Physics textbook for senior high school students, it is mentioned that from the earth’s point of view, the moon goes from round to missing and from missing to round. This is a cyclical change with a period of 29.5 days. Doubt: “When we talk about gravitation, does it mean that the moon’s orbit around the earth is 27.3 days? Why is it 29.5 days here?” To clarify this question, we must also talk about the moon’s movement around the earth and the earth’s movement around the sun. From.