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深藏在太阳中的氦是如何被发现的?

The Impossible Element Hiding in the Sun

《太空科学秀》
SciShow Space
我们早在八十年前就已经知道所有
We’ve known about all of the naturally occurring elements
天然存在的元素了
for at least 80 years,
从最熟悉的铁和碳元素
from the familiar ones like iron and carbon
再到最后一个发现的钫元素
to the very last one we found: francium.
这些元素大多是通过巧妙的化学实验发现的
Most of these elements werediscovered by doing clever chemistry.
但对于宇宙中第二大丰富的元素来说
But the second-most abundant element in the universe
其发现过程也同样独特
also has one of the most unique stories.
元素氦最先发现于太空中 其次才是地球
Helium was discovered in spacebefore it was found on Earth.
科学家用了近三十年的时间才接受
And it took nearly three decades for scientists to accept
“元素氦真的存在”这一事实
that it could actually exist.
氦是现在流行的气球填充气 能让人发出尖细的声音
The now-famous balloon filler and squeaky-voice-maker
最初发现于太阳大气层中 那时正值十九世纪六十年代
was first discovered in the atmosphere of the sun, back in the 1860s.
与此同时
Around the same time,
俄国化学家德米特里·门捷列夫正在研究
Russian chemist Dmitri Mendeleev was making what would soon become
未来权威的元素周期表
the standard periodic table
他根据已知元素的化学特性将其分门别类
by categorizing the known elements by their chemical properties.
他甚至在周期表中留下空位
He even left gaps in his table
给那些他预测会在未来某天被发现的元素
for elements he predicted would be discovered someday.
然而门捷列夫的周期表却不包括
But Mendeleev’s table didn’t include
那些如今被我们称为惰性气体的元素
the group of elements we now call the noble gases,
甚至连个空位也没留
or even a gap for them,
因为当时从未有人见过惰性气体
because no one had ever seen one.
氦气正是其中一种惰性气体
Helium is one of these noble gases:
这类元素相当不活跃
elements that are incredibly unreactive.
做这类实验可要多费一番工夫
It’s a struggle to do any chemistry with them at all,
因此这类元素也很难被发现
making them hard to detect.
也并不是因为地球大气层中仅含有
It doesn’t help that Earth’s atmosphere
百万分之五的氦气
is only about five parts per million helium, either.
但在太空中的情况却大相径庭
But in space it’s different.
如果你把宇宙看作一个整体
If you could look at the universe as a whole,
就会发现其中有75%的氢气
you would find that 75 % of it is hydrogen
和25%的氦气 其他气体则可以忽略不计
and 25% is helium, and everything else is negligible.
而太阳大气的成分与太空无异
The sun’s composition is similar.
那19世纪的人们是如何发现
So how can you detect an unknown element
那种不与任何物质反应
that doesn’t react with anything
而且几乎只存在于太空中的未知元素呢?
and basically only exists in space in the 19th century?
答案就是利用光谱学的技术
The answer lies in a technique called spectroscopy.
如果你将太阳光通过棱镜
If you put sunlight through a prism,
就会看到太阳光谱
you get a spectrum of light,
其中的可见光线呈现出彩虹色
with the visible part showing up as a rainbow.
1815年 德国物理学家约瑟夫·冯·夫琅和费
In 1815, a German physicist named Joseph von Fraunhofer
发现了意料之外的现象:
discovered something unexpected:
太阳光谱中有缺位!
the spectrum had holes in it!
夫琅和费看到光谱的特定位置上出现了黑线
Fraunhofer had seen dark lines at very precise points in the spectrum
看着有点像条形码
that looked kind of like a barcode.
这些黑线只在太阳光下出现
These lines only appeared in sunlight,
所以它们与条形码的功能也类似
so they also acted like a barcode:
你可以通过看光谱
you could distinguish sunlight
将太阳光和其它类型的光区分开
from other types of light by looking at the spectrum.
夫琅和费给这些黑线标上了A B C 以此类推
Fraunhofer labeled these lines A, B, C, and so on.
50年后 有两位科学家
And 50 years later, two scientists:
古斯塔夫· 基尔霍夫和罗伯特· 本生
Gustav Kirchhoff and Robert Bunsen,
利用本生新发明的本生灯完成了
made a revolutionary discovery about these lines
与黑线有关的革命性发现
using Bunsen’s new invention: the Bunsen burner.
通过燃烧不同的元素
By burning different elements,
基尔霍夫和本生发现
Kirchhoff and Bunsen discovered that
每种元素都集合了特定的黑线 形成了特定的光谱
each one had a unique collection of dark lines: a unique spectrum.
他们还发现
They also worked out
这种光谱的形成是因为元素吸收了光
that this spectrum was due to elements absorbing light,
但只吸收特定波长的光
but only at specific wavelengths.
更重要的是
And what’s more,
有些元素的黑线与太阳光中的黑线吻合
some of the elements’lines matched the lines that came from sunlight.
而太阳光谱是由其他元素的光谱组成的
The sun’s spectrum was composed of the spectrums of other elements.
例如基尔霍夫标记的两条线D1和D2
For instance, the two lines Fraunhofer labelled D1 and D2
同时出现在太阳光谱中的黄色区域
were in the yellow region of the solar spectrum,
和钠元素的光谱中
and they also appeared in the spectrum of sodium.
因此本生和基尔霍夫推断
So Bunsen and Kirchhoff concluded
太阳光中的D线
that the D lines from the sunlight
一定是太阳中的一小部分钠产生的
must have been caused by small amounts of sodium in the sun.
他们说对了
And they were right.
当他们意识到能用光谱学
Once they realized they could identify elements
识别太阳中的元素后
in the sun using spectroscopy,
其他科学家也开始研究太阳光谱了
other scientists got to workstudying the solar spectrum,
想找那些没被基尔霍夫发现的线
looking for more lines that Fraunhofer missed.
太阳光谱中有许多条线
There are lots of solar spectrum lines,
其中一条即将破土而出
but one line would soon stand out.
1868年 有两位研究者各自研究着日食
In 1868, two researchersindependently studied a solar eclipse.
日食挡住了太阳光中的主要部分
The eclipse blocked light from the main part of the sun,
这让两人得到了
allowing them to get a clear spectrum
太阳最外层——日冕层的清晰光谱
from the sun’s outermost layer, the corona.
由此 两人都在著名的钠D线旁
From this they both detected a line
发现了另一条线 名为D3
near the two well-known sodium D lines, called D3.
其中一人后来意识到
One of these researchers later realized
D3线并非来自钠
that the line wasn’t from sodium,
或其他已知元素
or from any known element,
因此他做了一个大胆的假设
and so he made the bold claim
认为这条线一定来自某个未知元素
that it must have been from an unknown element.
他将其命名为氦 以希腊太阳神赫利俄斯命名
He named it helium, after Helios,the Greek Sun god.
他甚至连接触都没接触到
He’d just discovered a new element
就发现了一种新元素
without ever getting his hands on the stuff!
当时这一发现颇具争议
For a while this discovery was controversial.
怎么能连分离都不做就发现了新元素呢?
How could you detect an element without a sample?
而且门捷列夫的元素周期表
Besides, Mendeleev’s periodic table had no room
并未给这样的新元素留位置
for a new element like this.
有人认为这条新线只是此前
Some said the new line was just a hydrogen line
被忽略的氢元素的线
that they’d previously missed.
因为氦太稀有 太不活跃了
Because helium is so rare and unreactive,
想分离出样品很难
it was hard to isolate a sample.
最终在1895年 伦敦大学学院的一名化学家
Eventually, in 1895, a chemistat University College London
在铀的放射性衰变中分离出了一种元素
isolated an element formed in theradioactive decay of uranium.
此元素中有独特的D3线
This element had the distinctive D3 line,
因此他推断此元素就是氦
so he concluded it had to be helium.
其实当时他在找另一种惰性气体氩气
He was actually looking for a different noble gas, argon, at the time,
不过 最终他也找到了
which he eventually found.
在发现了氦和氩之后
After the discovery of helium and argon,
门捷列夫坚定地把这两种稀有气体
Mendeleev was convinced to add the two noble gases to
加到了元素周期表中 分了新组
a new grouping on his periodic table.
上述这些发现都是
All these discoveries were made
在科学家了解光谱原理之前完成的
before scientists knew why spectrums worked this way.
而原理就由老朋友量子力学来告诉我们了
The answer turns out to be our old friend, quantum mechanics.
如今我们知道原子只能吸收和放射
We now know that atoms can only absorb and emit
某些特定波长的
particles of light, aka photons,
太阳光粒子 即光量子
if those photons are at certain specific wavelengths.
对一个原子来说 这些特定的波长独一无二
The precise wavelengths are unique to each type of atom,
因此每个原子都有区别于他者的光谱
so every atom has a different spectrum that can be used to identify it.
日食发生时 研究员看到了
During the eclipse, researchers were seeing
太阳大气层外层中的氦原子
helium atoms in the sun’s outer layer
在吸收内层放射的光线
absorbing light emitted from the lower layers,
而且只吸收特定波长的光线
and the absorption was happeningonly at distinct wavelengths.
如今 我们可以利用光谱学
Today, we can use spectroscopy to learn
去了解无他法可知的
about the composition of all kinds of things
任何事物的组成成分
we wouldn’t know much about otherwise.
从某种层面上来说
In some ways,
我们对遥远星系构成的认知
we have more information about the composition of distant galaxies
远超对地球内核的认知
than about the stuff in the core of our own planet.
我们也在尽力推动望远镜的发展
Telescopes are also starting to be advanced enough
以便应用光谱学技术
for us to use spectroscopy
进而研究在其他恒星轨道上运转的行星的大气层
to study the atmospheres of planets orbiting other stars.
也许我们已经发现了所有天然元素
Maybe we’ve found all the natural elements,
但我们对光谱学的认知
but we’ve barely scratched the surface
却还是九牛一毛
of what we can learn with spectroscopy.
感谢收看本期的《太空科学秀》
Thanks for watching thisepisode of SciShow Space,
感谢Patreon赞助本期节目!
which was brought to youby our patrons on Patreon!
如果想了解更多有关
For more awesome stories about
太空研究与探索的精彩故事
the history of space research and exploration,
尽在youtube.com/scishowspace 别忘了订阅
just go to youtube.com/scishowspaceand subscribe.

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视频概述

19世纪如何鉴定太阳成分?当时有光谱学技术吗?当时门捷列夫的元素周期表和现在一样吗?隐藏在太阳中的到底是哪种元素,让当时的科学家趋之若鹜?一切尽在本视频。

听录译者

收集自网络

翻译译者

未央lin

审核员

审核员BZ

视频来源

https://www.youtube.com/watch?v=GcfF40CPdl0

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