The moon illusion - Andrew Vanden Heuvel

月亮錯覺 - 安德魯‧凡登‧豪威爾

譯者: Kuanju Chou 審譯者: Justin Lin

Have you ever noticed

你有沒有注意過

how the full moon looks bigger

滿月在接近地平線時

when it's near the horizon

看起來比較大

than when it's high over head?

升上天頂的時候卻比較小？

If so, you're not alone.

不光是你這麼覺得

People have wondered about this strange effect

自古以來

大家一直對這個奇怪的現象感到好奇

since ancient times,

and surprisingly, we still don't have

而且驚人的是，我們還未找到

a great explanation,

一個極佳的解釋

but that's not for lack of trying.

但這不是因為沒有試著找答案

Some of the greatest minds in history -

許多歷史上數一數二的思想家

Aristotle,

亞里斯多德

Ptolemy,

托勒密

Da Vinci,

Decartes

達文西

笛卡爾

- have all wrestled with this problem

都苦思過這個問題

and failed to generate an adequate explanation.

卻無法得出合宜的解釋

One of the first ideas suggested

其中第一個想法認為

was that the image of the moon in the sky

天空中月亮的影像

really is bigger near the horizon.

在靠近地平線的時候的確比較大

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

或許地球的大氣層就像一面巨大的透鏡

magnifying the moon as it rises and sets.

能在月亮起落時將它放大

But this explanation doesn't cut it.

但這個解釋沒有切中要點

If anything, the refraction of the atmosphere

如果真是如此，大氣層的折射

would make the moon look slightly smaller.

會使月亮看起來稍微小一點

Plus, if you actually measure

再者，如果你實際測量

the size of the visible moon

月亮在不同位置的大小

at different positions,

你會發現

it doesn't change at all.

它根本沒有改變

But then, why does it still seem bigger

那麼為什麼當月亮升起時

when it's rising?

看起來比較大呢？

This must be some kind of optical illusion.

這必定是某種視錯覺

The question is, which one?

問題是，是哪一種呢？

One explanation is the Ebbinghaus Illusion,

艾賓浩斯錯覺是一種解釋

where two identical objects look different

兩件一樣的物體

because of the relative size

因周圍物體的相對大小

of the objects they're surrounded by.

而看起來不同

Here the two center circles are actually the same size.

這兩個位在中心的圓其實是一樣大的

Maybe the moon looks bigger near the horizon

或許月亮接近地平線時，看起來比較大

because it's next to tiny trees,

是因為它的旁邊有小樹

houses,

and towers in the distance.

房子

以及遠方的塔樓

But when the moon is higher up,

但當月亮升至高空時

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

被夜空中廣大的黑暗包圍

and looks tiny by comparison.

而在相互比較下，看起來較小

Another possibility is the famous Ponzo Illusion.

另一個可能的解釋是有名的龐佐錯覺

If you've ever tried to draw in perspective,

如果你曾嘗試以透視法作畫過

you know that the closer something is to the horizon,

你就知道你應該將愈靠近地平線的東西

the smaller you should draw it.

畫得愈小

Our brain compensates automatically for this

我們的腦袋自動補償了這個現象

by perceiving objects near the horizon

藉由將接近地平線的物體

as larger than they actually appear.

看成比實際上來得大

The two yellow lines in this drawing

圖畫中的兩條黃線

are the same size,

大小一樣

but the upper one seems bigger

但上面的線段看起來比較大

because we interpret it as receding

因為我們將它解釋為

farther into the horizon.

退向遠方的地平線

So, between Ponzo and Ebbinghaus,

那麼，透過龐佐還有艾賓浩斯

it seems like we've solved the mystery

我們似乎已經解決了

of the moon illusion,

月亮錯覺的謎團

but, unfortunately, there are a few details

但不幸地，有一些細節

that complicate things.

使得月亮錯覺更加令人費解

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

一方面，如果這只是艾賓浩斯錯覺的話

then we would expect the moon illusion

我們會預期月亮錯覺

to disappear for pilots flying high above the clouds

在飛航員於雲端飛行時會消失

since there wouldn't be any other smaller objects

因為那裡並沒有其他靠近地平線的

near the horizon.

較小物體

But in fact, pilots and sailors out on the ocean

但實際上，飛行員和海上的航海員

still claim to see the moon illusion.

都宣稱看過月亮錯覺

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

另一方面，若這只是我們腦內自動在校正

the size of objects near the horizon,

靠近地平線物體的大小

then we'd expect the moon illusion

那麼我們會期待月亮錯覺

to be visible inside a planetarium,

在天文館也看得到

where the whole sky,

那裡的整個天空

including the horizon,

包含地平線在內

is displayed on a spherical dome overhead.

都展現在球形圓頂的上頭

Studies have shown, though,

然而，研究顯示

that this is not the case.

情況不是如此

To make matters worse,

更麻煩的是

it seems the moon illusion disappears entirely

月亮錯覺似乎

if you just bend over

會在你彎下腰來

從雙腿間看月亮時完全消失

and look at the moon between your legs.

Now, this is just getting ridiculous!

現在開始一發不可收拾了！

One of the most promising explanations today

今日，其中一項最具前瞻性的解釋

is known as Convergence Micropsia.

叫做視物顯小理論

Our brains judge the distance to objects

我們的大腦藉由將雙眼聚焦

and their apparent size

來判斷物體的距離

by the focus of our eyes.

以及它們外觀的大小

When looking at the horizon,

看向地平線時

your eyes focus far off into the distance

眼睛聚焦在遙遠的遠方

so your brain knows you're looking far away.

所以你的大腦知道你在看遠方

The moon appears a certain size.

月亮看起來是一定的大小

Your brain thinks it's far away,

你的大腦認為它非常遠

which it is,

所以

so you naturally conclude the moon must be big.

你自然而然認為月亮一定很大

But when looking up at the night sky,

但當你抬頭看向夜空

there's nothing for your eyes to focus on,

那裡沒有東西可以讓眼睛聚焦

so they default to their rest focus,

所以雙眼默認了其餘的焦距

which is a point just a few meters away.

也就是幾公尺之外的一點

Now your brain thinks the moon is much closer

現在你的大腦認為月亮比實際上

than it really is,

距離你更近

so you naturally conclude

所以你自然而然地認為

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

月亮並沒有你原先想的那麼大

Rather than explain why the moon

視物顯小理論沒有解釋

looks so big near the horizon,

為什麼月亮靠近 地平線時看起來較大

Convergence Microspia explains

而對為何月亮在頭頂上方時

why the moon looks so small when overhead.

看起來較小做了解釋

Still not satisfied?

還是不滿意嗎?

Well, frankly, neither are many scientists,

好吧，坦白說，很多科學家也不甚滿意

so the debate over the moon illusion still rages on

所以月亮錯覺的爭論還在持續著

and may continue as long as we still see it

而且只要夜裡還看得到月亮

in the night sky.

就會一直持續下去