If you look up at the patches of murk between buildings,

如果你抬頭看看建築物間的小塊夜空，

you might be able to pick out The Big Dipper,

你或許能找出北斗七星，

or perhaps, Orion's Belt.

或者是獵戶座腰帶。

But hold on.

不過等等，

Look at that murky patch again and hold out your thumb.

再仔細看看那片黑夜， 伸出你的大拇指，

How many stars do you think are behind it?

你覺得你蓋住了多少恆星？

Ten, twenty? Guess again.

十顆？二十顆？再猜一猜。

If you looked at that thumbnail-sized patch of sky

如果你用哈勃天文望遠鏡

with the Hubble Space Telescope,

去看那片拇指大小的天空，

instead of points of light, you'd see smudges.

你不會看到許多小亮點， 而是看到一團團光暈。

These aren't stars.

而這些光暈不是恆星，

They're galaxies, just like our Milky Way.

它們是星系，就像我們的銀河系一樣，

Cities of billions of stars,

每個都是好幾十億恆星的群落，

and more than 1,000 of them are hidden behind your thumb.

在你大拇指底下，就有超過一千個星系。

The universe is bigger than you can see from the city,

宇宙的規模比你從城市裡所見的還要巨大，

and even bigger than the starry sky you can see from the countryside.

甚至比你從鄉間所望見的星空還要浩瀚。

This is the universe as astrophysicists see it,

這就是天文物理學家眼中的宇宙，

with more stars than all the grains of sand on Earth.

裡面的恆星比地球上的沙粒還要多。

By staring up at the stars at night,

每當你在夜晚仰望星空時，

you've taken part in the oldest science in human history.

你實際上是在參與人類史上最古老的科學活動。

The study of the heavens is older than

天文研究在人類史上

navigation, agriculture, perhaps even language itself.

比航海、農業、可能比語言的存在還要古老。

Yet unlike other sciences, astronomy is purely observational.

但不像其他科學，天文學的基礎完全只憑觀測。

We cannot control the parameters of our experiments from lab benches.

我們無法在實驗室控制任何變因或參數。

Our best technology can send man to the moon,

用最尖端的科技，我們可以送人類上月球

and probes to the edge of the solar system.

並探勘太陽系的邊界，

But these distances are vanishingly small

但比起星辰間的無垠地帶，

compared to the yawning gulfs between stars.

人類所能探觸的距離簡直微不足道。

So how can we know so much about other galaxies,

所以我們怎麼獲得大量其他星系的知識呢？

what they're made of, how many there are, or that they're even there at all?

我們怎麼知道它們的成分、數量， 甚至確定它們存在？

Well, we can start with the first thing we see when we look up at night: the stars.

好吧，我們可以先從仰望天空 最先看到的東西開始：星星。

What we are trying to learn is their properties.

我們試著了解它們的特質。

What are they made of? How hot are they? How massive? How old?

它們的成分是甚麼？溫度多高？ 規模多大？存在了多久？

How far are they from Earth?

它們離地球的距離有多遠？

And believe it or not,

信不信由你，

we can learn all of these things simply from the light shining in the sky.

這些答案都可以從星星發出的光芒推算出來。

We can decipher one kind of stellar message by turning starlight into rainbows.

我們將這些星光轉換為彩虹光譜， 就可以破解這些星辰背後的秘密。

When you look at a rainbow on Earth,

當你在地球上看到彩虹的時候，

you're really looking at light from our Sun

其實你看到的是太陽所發出的光，

being scattered through water droplets in the atmosphere

被大氣層的水珠折射後所散發的光譜，

into all the different wavelengths that make it up.

水珠將光線分散成不同的波長，形成彩虹。

And we study the light from other stars,

所以當我們分析其他星球的光芒時，

we can create rainbows on demand using not water droplets,

我們可以自己將它變成彩虹，但不是用水珠，

but other specific instruments that disperse light.

是用其他分散光譜的儀器。

When we look at the scattered light from our sun,

當我們仔細觀察太陽光的彩虹光譜時，

we see something strange: dark lines in our rainbow.

有個奇怪的現象：彩虹光裡有一些黑線。

These lines are the characteristic fingerprints of atoms.

這些黑線就像指紋一樣，是原子的特有的波紋。

Each type of atom in the solar atmosphere soaks up light at specific wavelengths,

在大氣層中， 每一種原子只會吸收某段特定波長的光，

and the amount of absorption depends on how many of these atoms there are.

這些波長的光被吸收的量， 取決於該原子數量的多寡。

So by observing how much light is missing at these characteristic wavelengths,

所以如果我們觀察在這個特定波長裡， 有多少光不見了，

we can tell not only what elements are in the Sun's atmosphere,

我們不只可以推斷出 太陽系大氣層裡有哪些元素，

but even their concentrations.

甚至還可以推算出元素所占的比例。

And the same idea can be applied to study other stars.

同樣的方法也可運用於其他恆星：

Make a spectral rainbow, see what's missing,

將恆星的彩虹光譜分析出來， 看看裡面缺少那些波段，

and figure out which elements are present.

就可推算出有那些元素的存在。

Bingo. Now you know what stars are made of.

太好了，現在你知道恆星的成分了。

But we aren't restricted to just the wavelengths that our eyes perceive.

儘管我們眼睛的可見光有限， 我們並不會被此限制，

Consider radio waves.

試想，還有無線電波呢。

Yes, they can bring the Billboard Top 100 to your car,

是的，無線電波可以讓你 在車上聽廣播金曲排行榜，

but they can also travel almost unimpeded through space.

但這種波也可以在太空中自由傳遞，

Because they've come so far,

而因為它們是從太空中非常遠的地方傳來，

radio waves can tell us the very early history of the universe,

無線電波可以告訴我們宇宙非常早期的歷史，

from just a few thousand years after The Big Bang.

甚至可以追朔到 宇宙大爆炸後僅幾千年的時間。

We can also study the infrared light, emitted by colder objects,

我們也可以研究其他比較冷的物體 所發出來的遠紅外線，

like the gas and dust clouds in space,

像是太空中的氣體和塵雲，

and the ultraviolet light from the hot stars recently born from those clouds.

也可以觀察剛誕生的、 比較熱的恆星所發出來的紫外線光。

Studying different wavelengths not only gives us

研究不同的波長，不但可以讓我們

a more complete picture of any single object

對一個物體有更全面的了解，

but also different views of the universe.

也可以讓我們對宇宙有不同的認識。

For this reason, astrophysicists use several different kinds of telescopes

因此，天文物理學家運用了幾種不同的望遠鏡，

covering the spectrum from the infrared to the ultraviolet to the X-ray,

好讓他們可以完整觀察各種光線， 包含遠紅外線、紫外線和X光射線，

from giant radio dishes to giant silver mirrors to space satellites,

接收的媒介包含巨型的無線電接收器、 反射鏡和人造衛星，

detecting light that would be otherwise blocked by the Earth's atmosphere.

這些可以偵測到 原本地球大氣層收不到的東西。

Astrophysicists don't just see

天文物理學家不只可以看見

the billions of stars among the billions of galaxies in the universe.

宇宙中好幾十億的星系中好幾十億的恆星，

They hear, feel and sense them through many channels,

他們也可以透過各種媒介聽見、 觸及、感覺到這些星球的存在。

each revealing a different story.

每一個恆星都訴說著不同的故事。

But it all begins with light, the kind we can see and the kind we can't.

但這一切都是從光開始的， 有些光我們看得見，有些我們看不見。

Want to know the secrets of the Universe?

想知道宇宙的祕密嗎？

Just follow the light.

就追隨光吧。