The moon illusion - Andrew Vanden Heuvel

月球错觉 - Andrew Vanden Heuvel

翻译人员: Xuwen Zhu 校对人员: Peipei Xiang

Have you ever noticed

你注意到了吗？

how the full moon looks bigger

满月在接近地平线时

when it's near the horizon

比高挂于空中时

than when it's high over head?

看起来大一些。

If so, you're not alone.

如果注意到了这点，你不是唯一一个。

People have wondered about this strange effect

人们长久以来对这个奇怪的现象

since ancient times,

惊奇不已，

and surprisingly, we still don't have

惊讶的是，我们仍然

a great explanation,

没有一个很好的解释。

but that's not for lack of trying.

这不是因为我们没有努力去寻找解释，

Some of the greatest minds in history -

历史上一些最伟大的头脑，

Aristotle,

亚里士多德，

Ptolemy,

托勒密，

Da Vinci,

Decartes

达芬奇

笛卡尔，

- have all wrestled with this problem

他们都曾经尝试解释这个问题

and failed to generate an adequate explanation.

却都铩羽而归。

One of the first ideas suggested

最早的想法中有这样一种：

was that the image of the moon in the sky

月亮在空中成的像

really is bigger near the horizon.

确实在接近地平线时大一些。

Perhaps the Earth's atmosphere acts like a giant lens,

或许地球的大气层就像一面巨大的透镜，

magnifying the moon as it rises and sets.

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

如果真有大气层折射，

would make the moon look slightly smaller.

那也应该让月亮看起来小一点。

Plus, if you actually measure

而且，如果你真的

the size of the visible moon

在不同地点

at different positions,

测量月亮可见部分的尺寸，

it doesn't change at all.

会发现其实都是一样的。

But then, why does it still seem bigger

那么，究竟是为什么

when it's rising?

当月亮升起时会显得大一些？

This must be some kind of optical illusion.

一定是一些光学上的错觉。

The question is, which one?

问题是，哪一种错觉？

One explanation is the Ebbinghaus Illusion,

一种解释是艾宾浩斯错觉，

where two identical objects look different

这是指两个相同的物体

because of the relative size

会因为它们和周围物体的相对尺寸

of the objects they're surrounded by.

而显得不一样大。

Here the two center circles are actually the same size.

这里，中心的两个圆事实上是一样大的。

Maybe the moon looks bigger near the horizon

或许月亮在接近地面时显得大

because it's next to tiny trees,

是因为它边上有小树，

houses,

and towers in the distance.

房子，

和远处的塔楼。

But when the moon is higher up,

而当月亮在高空中时，

it's surrounded by the vast darkness of the night sky

它被茫茫黑夜环绕，

and looks tiny by comparison.

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,

如果你曾经试过透视画法

you know that the closer something is to the horizon,

就会知道，一样东西越靠近地平线

the smaller you should draw it.

就该画得越小。

Our brain compensates automatically for this

我们的大脑自动弥补了这样的透视效果，

by perceiving objects near the horizon

使得地平线附近的物体

as larger than they actually appear.

在我们脑海中的形象比实际更大。

The two yellow lines in this drawing

这幅画里两条黄线

are the same size,

是一样的尺寸，

but the upper one seems bigger

但上面那一条看起来更长，

because we interpret it as receding

因为我们觉得它更接近地平线，

farther into the horizon.

所以应该比画里面显得更长。

So, between Ponzo and Ebbinghaus,

那么，通过庞佐和艾宾浩斯错觉

it seems like we've solved the mystery

我们似乎已经解决了

of the moon illusion,

这个月球错觉问题。

but, unfortunately, there are a few details

但不幸的是，还有一些细节

that complicate things.

让事情不那么简单。

For one thing, if this was just the Ebbinghaus effect,

举例说，如果真是艾宾浩斯效应，

then we would expect the moon illusion

那么我们应该预期，月球错觉

to disappear for pilots flying high above the clouds

对于在空中的飞行员不起作用，

since there wouldn't be any other smaller objects

因为对他们来说，在地平线附近

near the horizon.

没有什么小物体可以用来作比较。

But in fact, pilots and sailors out on the ocean

但事实上，飞行员和大洋上的水手

still claim to see the moon illusion.

仍声称看到了这个月球错觉。

On the other hand, if it's just our brain's autocorrecting

另一方面，如果这只是因为我们大脑的自动纠正功能

the size of objects near the horizon,

使得地平线附近的物体尺寸有变化，

then we'd expect the moon illusion

那么我们应该预期，

to be visible inside a planetarium,

月球错觉在天文观测台内仍然有效，

where the whole sky,

在那里，

including the horizon,

整个天空包括地平线，

is displayed on a spherical dome overhead.

都在头顶的球形屋顶上。

Studies have shown, though,

但是研究表明

that this is not the case.

并不是这样。

To make matters worse,

更糟的是，

it seems the moon illusion disappears entirely

如果你弯下腰，

if you just bend over

从两腿之间看月亮，

and look at the moon between your legs.

月球效应似乎完全消失了。

Now, this is just getting ridiculous!

这岂不是荒谬！

One of the most promising explanations today

目前最有希望的解释之一是

is known as Convergence Micropsia.

聚焦视野显小症。

Our brains judge the distance to objects

我们的大脑通过

and their apparent size

眼睛的聚焦

by the focus of our eyes.

来决定与物体的距离以及他们的尺寸。

When looking at the horizon,

当我们看地平线时，

your eyes focus far off into the distance

眼睛聚焦在极远的地方，

so your brain knows you're looking far away.

这样你的大脑就知道你在看远方。

The moon appears a certain size.

这时月亮有一个固定的尺寸，

Your brain thinks it's far away,

你的大脑认为月亮在很远的地方，

which it is,

它确实是很远，

so you naturally conclude the moon must be big.

所以你自然认为月球一定很大。

But when looking up at the night sky,

但是当你看天空的时候，

there's nothing for your eyes to focus on,

没有东西可以让你的眼睛聚焦，

so they default to their rest focus,

所以眼睛自动聚焦到了平常的焦点，

which is a point just a few meters away.

这距离你只有几米。

Now your brain thinks the moon is much closer

现在你的大脑认为月球距离你很近

than it really is,

远比实际距离要近，

so you naturally conclude

所以你的大脑自然认为

the moon's not as big as you thought it was.

月球并没有你想象的那么大。

Rather than explain why the moon

尽管它并没有解释为什么

looks so big near the horizon,

月球在地平线附近显得大，

Convergence Microspia explains

但聚焦视野显小症解释了

why the moon looks so small when overhead.

为什么月球在空中看起来显得小。

Still not satisfied?

还是不满意？

Well, frankly, neither are many scientists,

好吧，老实说，很多科学家也不满意。

so the debate over the moon illusion still rages on

所以关于这个现象的争论仍在继续，

and may continue as long as we still see it

说不定只要我们一日能见到夜空中的月球，

in the night sky.

这争论就一日都不会停止。