before seen: the far side of the moon.

月球的背面

We always see the same old side of the moon because the moon rotates exactly once on its

我們總是看到同一面的月球，因為月球自轉一圈的時間恰等於公轉地球一周

axis each time it orbits Earth. If it weren’t spinning at all, we’d get at least one 360

如果它完全不自轉，每次月球公轉一周我們都能至少看到一次月亮的全貌

degree view of its surface with each lap. If it were spinning twice as fast, we’d

如果月球以兩倍速自轉

also see the moon’s entire surface more than once per orbit. But instead, our moon’s

那每次月球公轉一周時，我們可以看到月球全貌不只一次

motions – like the spin and orbit of most other moons in our solar system – are, remarkably,

然而，月球的運行—正如太陽系中大多數衛星的自轉公轉週期—

in perfect sync.

非常完美地同步

This wasn’t always the case: our best guess is that our own moon formed due to a massive

但這情況不是絕對：目前最佳的推測是，我們的月球是由小行星撞擊而形成的

asteroid impact, and its initial spin and dizzying 10-hour orbit were almost certainly

而它最初的自轉週期和極快的10小時/次公轉週期

not in sync with each other – though we don’t know which was faster.

兩者基本上並未同步，但我們不知道哪個比較快

At such close range, Earth’s gravity deformed the moon into a slight oval, with one of its

在如此近的距離下，地球引力使月球變形、略顯橢圓，其中一端突起朝向地球

bulges facing Earth. Those bulges quickly swung out of alignment, thanks to the moon's

這兩端突起因為自轉公轉不同步而被甩離地球

asynchronous spin and orbit, but Earth’s gravity continually squeezed them back again.

但地球引力又不斷將它拉回來

What’s more, this gravitational tugging would have influenced the moon’s rotation

更重要的是，這引力拉扯影響了月球的自轉頻率：

rate: if it was spinning more than once per orbit, earth would pull at a slight angle

若它公轉一周內自轉超過一次，則地球會輕微地

against the moon’s direction of rotation, slowing its spin; if the moon was spinning

以月球自轉的反方向拉扯它，以減低其轉速

less than once per orbit, Earth would have pulled the other way, speeding its rotation.

若是月球公轉一周內自轉少於一次，地球會順著月球自轉方向拉扯、增加轉速

Whatever the case, it took just 1000 years for the Earth’s pull to adjust the moon’s

無論如何，地球只花了一千年就以拉扯的方式

spin enough that one rotation of the moon corresponded to one trip around the earth,

將月亮調整為自轉一圈等於公轉一周

leaving one side forever locked facing away.

使月亮另一邊永遠被固定在背面

We do end up seeing slightly more than that one side, because the moon’s elliptical

我們最後其實能看到比一面多一點的月球，因為月球的橢圓軌道

orbit gives us peeks beyond its average eastern and western horizons, and its tilted axis

讓我們能窺見比平均的東(西)半球更多一點的地方

causes “moon-seasons” revealing more of the lunar north or south poles. But those

而它傾斜的自轉軸造成了「月亮季節」，使得月亮的南北極露出更多部分

glimpses only add up to an extra 9%, leaving 41% of the moon hidden from earth. Satellites,

但是這些驚鴻一瞥只能讓我們多看到9%的月亮，仍有41%無法從地球看見

starting with Luna 3, have allowed us to map the rest, but it’s safe to say that our

從月球三號開始，人造衛星讓我們可以描繪原本不可見的月亮

relationship with the moon is still pretty one-sided.

然而我們與月亮的關係仍舊如單戀般「片面」