The moon illusion - Andrew Vanden Heuvel

Translator: Hafizh Alfarisi Reviewer: Reno Kanti Riananda

Have you ever noticed

Apa kau pernah memperhatikan besarnya bulan purnama

how the full moon looks bigger

when it's near the horizon

saat berada di dekat horizon daripada saat berada di atas langit?

than when it's high over head?

If so, you're not alone.

Jika begitu, kau tidak sendirian.

People have wondered about this strange effect

Orang-orang mempertanyakan fenomena ganjil ini sejak zaman kuno.

since ancient times,

and surprisingly, we still don't have

Mengejutkannya, kita masih belum punya cukup penjelasan,

a great explanation,

but that's not for lack of trying.

tetapi bukan karena kurangnya usaha.

Some of the greatest minds in history -

Beberapa pemikir terhebat dalam sejarah— Aristotle, Ptolemy, Da Vinci, Descartes—

Aristotle,

Ptolemy,

Da Vinci,

Decartes

- have all wrestled with this problem

telah bergulat dengan masalah ini dan gagal memberikan penjelasan memadai.

and failed to generate an adequate explanation.

One of the first ideas suggested

Salah satu pendapat pertama mengemukakan citra bulan di langit

was that the image of the moon in the sky

really is bigger near the horizon.

lebih besar ketika di dekat horizon.

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

Mungkin atmosfer Bumi berperan seperti lensa raksasa,

magnifying the moon as it rises and sets.

memperbesar bulan saat terbit dan terbenam.

But this explanation doesn't cut it.

Namun, penjelasan ini belum cukup.

If anything, the refraction of the atmosphere

Andaikan begitu, pembelokan cahaya dari atmosfer

would make the moon look slightly smaller.

akan membuat bulan terlihat agak mengecil.

Plus, if you actually measure

Kalau pun kau menghitung ukuran bulan yang terlihat pada posisi berbeda,

the size of the visible moon

at different positions,

it doesn't change at all.

ukurannya tak berubah.

But then, why does it still seem bigger

Kalau begitu, kenapa bulan masih terlihat lebih besar saat terbit?

when it's rising?

This must be some kind of optical illusion.

Ini pasti semacam ilusi optik.

The question is, which one?

Pertanyaannya adalah yang mana?

One explanation is the Ebbinghaus Illusion,

Salah satu penjelasannya adalah Ilusi Ebbinghaus,

where two identical objects look different

di mana dua objek sama terlihat berbeda karena ukuran relatif

because of the relative size

of the objects they're surrounded by.

benda-benda yang mengelilinginya.

Here the two center circles are actually the same size.

Di sini, dua pusat lingkaran aslinya berukuran sama.

Maybe the moon looks bigger near the horizon

Mungkin bulan terlihat lebih besar di dekat horizon

because it's next to tiny trees,

karena di antara beberapa pohon kecil, rumah, dan menara di kejauhan.

houses,

and towers in the distance.

But when the moon is higher up,

Namun saat lebih tinggi, bulan dikelilingi luasnya gelap dari langit malam

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

and looks tiny by comparison.

dan terlihat kecil dalam perbandingannya.

Another possibility is the famous Ponzo Illusion.

Kemungkinan lainnya adalah Ilusi Ponzo yang terkenal.

If you've ever tried to draw in perspective,

Jika kau pernah menggambar sesuai sudut pandang,

you know that the closer something is to the horizon,

kau tahu semakin dekat benda ke horizon, semakin kecil kau menggambarnya.

the smaller you should draw it.

Our brain compensates automatically for this

Otak kita langsung membenarkan hal ini dengan menganggap objek di dekat horizon

by perceiving objects near the horizon

as larger than they actually appear.

lebih besar daripada aslinya.

The two yellow lines in this drawing

Dua garis kuning di gambar berukuran sama, tetapi garis atas terlihat lebih besar

are the same size,

but the upper one seems bigger

because we interpret it as receding

karena kita menganggapnya menyurut ke dalam horizon.

farther into the horizon.

So, between Ponzo and Ebbinghaus,

Di antara Ponzo dan Ebbinghaus, sepertinya kita telah memecahkan misteri ilusi bulan.

it seems like we've solved the mystery

of the moon illusion,

but, unfortunately, there are a few details

Namun sayangnya, ada sedikit rincian yang memperumit beberapa hal.

that complicate things.

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

Misalnya, jika ilusi ini hasil efek Ebbinghaus,

then we would expect the moon illusion

kita akan menduga ilusi bulan menghilang

to disappear for pilots flying high above the clouds

bagi pilot yang melayang tinggi di atas awan-awan

since there wouldn't be any other smaller objects

karena tidak akan ada benda lebih kecil di dekat horizon.

near the horizon.

But in fact, pilots and sailors out on the ocean

Namun, pilot dan pelaut di tengah samudra mengaku masih melihat ilusi bulan itu.

still claim to see the moon illusion.

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

Di sisi lain, jika cuma otak kita yang langsung mengoreksi

the size of objects near the horizon,

ukuran benda-benda di dekat horizon,

then we'd expect the moon illusion

lalu kita akan menduga ilusi bulan terlihat di dalam planetarium,

to be visible inside a planetarium,

where the whole sky,

di mana seluruh langit, termasuk horizon,

including the horizon,

is displayed on a spherical dome overhead.

ditampilkan pada kubah bundar di atas kepala.

Studies have shown, though,

Meski begitu, studi menunjukkan bahwa ini bukan masalahnya.

that this is not the case.

To make matters worse,

Lebih buruknya lagi, kelihatannya ilusi bulan menghilang seutuhnya

it seems the moon illusion disappears entirely

if you just bend over

jika kau membungkuk dan melihat bulan di antara kedua kakimu.

and look at the moon between your legs.

Now, this is just getting ridiculous!

Sekarang, ini semakin konyol!

One of the most promising explanations today

Salah satu penjelasan menjanjikan saat ini dikenal sebagai Convergence Micropsia.

is known as Convergence Micropsia.

Our brains judge the distance to objects

Otak kita menilai jarak ke objek dan ukurannya yang terlihat

and their apparent size

lewat fokus kedua mata kita.

by the focus of our eyes.

Saat melihat horizon, matamu berfokus ke tempat jauh

When looking at the horizon,

your eyes focus far off into the distance

so your brain knows you're looking far away.

sehingga otakmu tahu kau sedang melihat kejauhan.

The moon appears a certain size.

Bulan terlihat dalam ukuran tertentu.

Your brain thinks it's far away,

Otakmu berpikir bulan berada jauh, memang begitu,

which it is,

so you naturally conclude the moon must be big.

jadi kau segera menyimpulkan bulan pastinya besar.

But when looking up at the night sky,

Namun saat melihat langit malam, tak ada benda yang bisa difokuskan matamu,

there's nothing for your eyes to focus on,

so they default to their rest focus,

jadi matamu menuju fokus yang ada, berupa titik yang cuma beberapa meter.

which is a point just a few meters away.

Now your brain thinks the moon is much closer

Sekarang otakmu berpikir bulan lebih dekat dari kelihatannya,

than it really is,

so you naturally conclude

jadi kau segera menyimpulkan bila bulan tidak sebesar yang kau duga.

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

Rather than explain why the moon

Ketimbang menjelaskan kenapa bulan terlihat besar di dekat horizon,

looks so big near the horizon,

Convergence Microspia explains

Convergence Microspia menjelaskan kenapa bulan terlihat kecil saat ada di atas.

why the moon looks so small when overhead.

Still not satisfied?

Masih belum puas? Sebenarnya, banyak ilmuwan yang belum puas.

Well, frankly, neither are many scientists,

so the debate over the moon illusion still rages on

Jadi, perdebatan soal ilusi bulan masih memanas

and may continue as long as we still see it

dan mungkin berlanjut selama kita masih melihatnya di langit malam.

in the night sky.