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Have you ever noticed how the full moon looks bigger when it's near the horizon than when it's high over head?
你注意到了吗？满月在接近地平线时比高挂空中时看起来大一些。
If so, you're not alone.
如果你注意到了，你就不孤独了。
People have wondered about this strange effect since ancient times, and surprisingly, we still don't have a great explanation, but that's not for lack of trying.
人们长久以来对这个奇怪现象惊奇不已，令人惊讶的是，我们仍然没有一个完美解释，但这不是因为我们没有努力去寻找解释。
Some of the greatest minds in history, Aristotle, Ptolemy, Da Vinci, Decartes, have all wrestled with this problem and failed to generate an adequate explanation.
历史上的一些伟人，如亚里士多德、托勒密、达芬奇笛卡尔，都曾试过解释这个问题，却都铩羽而归。
One of the first ideas suggested was that the image of the moon in the sky really is bigger near the horizon.
最初的一种观点是月亮在空中时成的像确实比接近地平线时大一些。
Perhaps the Earth's atmosphere acts like a giant lens, magnifying the moon as it rises and sets.
或许地球的大气层就像一面巨大透镜，在月亮升起和降落时放大它的图像。
But this explanation doesn't cut it.
但是这个解释并不合理。
If anything, the refraction of the atmosphere would make the moon look slightly smaller.
如果真有大气层折射，它应该是让月亮看起来小一点儿。
Plus, if you actually measure the size of the visible moon at different positions, it doesn't change at all.
而且，如果你真的在不同地点测量月亮可见部分的尺寸，会发现它没有变化。
But then, why does it still seem bigger when it's rising?
那么，为什么月亮升起时会显得大一些呢？
This must be some kind of optical illusion.
这一定是某种视错觉。
The question is, which one?
问题是，是哪一种视错觉？
One explanation is the Ebbinghaus Illusion, where two identical objects look different because of the relative size of the objects they're surrounded by.
一种解释是艾宾浩斯错觉，即两个相同的物体会因为它们与周围物体的相对尺寸而显得不一样大。
Here the two center circles are actually the same size.
这两个中心圆事实上一样大。
Maybe the moon looks bigger near the horizon because it's next to tiny trees, houses, and towers in the distance.
或许月亮在接近地面时显得大是因为它附近有小树、房子和远处的塔楼。
But when the moon is higher up, it's surrounded by the vast darkness of the night sky and looks tiny by comparison.
而当月亮在高空中时，它被茫茫黑夜环绕，所以相对来说显得小了。
Another possibility is the famous Ponzo Illusion.
另一种解释是著名的庞佐错觉。
If you've ever tried to draw in perspective, you know that the closer something is to the horizon, the smaller you should draw it.
如果你曾经试过透视画法就会知道，一样东西越靠近地平线就该画得越小。
Our brain compensates automatically for this by perceiving objects near the horizon as larger than they actually appear.
我们的大脑自动弥补了这样的透视效果，使得地平线附近的物体在我们脑海中的形象比实际更大。
The two yellow lines in this drawing are the same size, but the upper one seems bigger because we interpret it as receding farther into the horizon.
这幅画里两条黄线是一样的尺寸，但上面那一条看起来更长，因为我们觉得它更接近地平线，所以应该比画里面显得更长。
So, between Ponzo and Ebbinghaus, it seems like we've solved the mystery of the moon illusion, but, unfortunately, there are a few details that complicate things.
那么，通过庞佐和艾宾浩斯错觉，我们似乎解决了这个月球错觉的问题，但不幸的是，还有一些细节让事情不那么简单。
