好問題，謝提問！答案有點兒繞腦但很有趣。見這裏：。。。

Earth and moon each orbits at its own axis, and there is a angle between them:

as a result, the moon will return to the same position in the sky about 50 min and 29 s later each night. Therefore in the picture, since the moon was photoed from the same location on earth and at the same time each night over a month, it would not appear at the same position in the sky where it appeared 30 days ago.

To take a picture of the moon that will show it appearring at the same position 30 days ago - following the pattern of 8 and known as a "analemma", one has to take a picture of it each night 50min29s later than last night. Then the moon's path in the sky over a month will be an analemma:

 

 

所有跟帖： 

• 這個我明白，但是你的照片還是不對。如果一個月內都是固定一個時刻拍照，月亮的仰角會差別很大，有的日子根本拍不到 -aguafresh- ♂ (191228 bytes) () 08/23/2023 postreply 08:59:43

• 簡單一個例子，每隔農曆半個月的同一個時分，月亮的位置差約180度，如果你今天拍了，半個月以後就肯定拍不著 -aguafresh- ♂ (192 bytes) () 08/23/2023 postreply 09:27:06