Moonrise above the Lake
On the eve of July 16, 2019, I was treated to a special moment when the full moon rose above Lake Constance in Southern Germany. And with it came the recurring question: Why is the full moon bigger at the horizon? Well, the answer is short: It isn’t. This is just an optical illusion that is triggered by the fact that we see objects at the horizon (such as trees or buildings) and compared to these the moon seems large. When we observe the moon when it is higher in the sky these references are missing and the moon appears smaller. But when you measure it (e.g. on a photo) you will soon realize that the actual size remains the same.
