评论
打印
Through the history of space exploration so far,
纵观我们的太空探索历程，
we've debated where the earth's atmosphere ends, and space begins.
我们已经讨论过地球大气层的尽头兼外太空的起点这一问题了。
And your surprise for the day is that according to newly unearthed observations,
出人意料的是，最新的观测结果显示，
our atmosphere is way bigger than we ever thought.
我们的大气层比我们想象的要大得多。
Like it goes past the moon.
具体来讲就是……大到月球都落在它的范围之内。
We've mostly defined space as the vast expanse of the rest of the universe that exists past the Karman Line,
我们对太空的主要定义是，卡门线，位于海拔100km左右处，
which exists roughly 100 kilometers above mean sea level.
以外的浩瀚宇宙。
Now according to Federation Aeronautique Internationale—the organization officially in charge of determining these kinds of rules—
国际航空联合会(FAI)，就是负责确立这些规则的官方机构，
after the Karman line, you are in space.
规定过了卡门线，你就到外太空了。
The reasoning behind this is after 100 kilometers,
这么规定的原因是，在纬度高于海拔100km的地方，
the earth's atmosphere becomes too thin
地球的大气层会逐渐变得稀薄，
for a conventional aeronautic vehicle like an airplane to stay in flight without reaching orbital velocity—
飞机这样的常规航空飞行器没有达到轨道速度就无法继续飞行了，
so you have to switch to more specialized astronautic vehicles.
这样一来，你就必须换乘更专业的航天飞行器。
But if you thought this was gonna be simple—it's not.
但如果你以为这里面的学问很简单，那你就错了。
Even though the FAI's Karman line designation is commonly recognized,
尽管FAI划定的卡门线已经得到了普遍认可，
there's actually no official international consensus over where space technically begins.
但实际上，在外太空确切的起点问题上，国际社会并没有达成正式的共识。
Some astrophysicists say it should actually be 80 kilometers above the mean sea level
一些天体物理学家认为，从轨道动量作用于卫星物体的方式来看，
because of the way that orbital momentum acts on satellite objects.
这一界线实际应该划在海拔80km的地方。
NASA and the U.S. air force also define space as starting about 80 kilometers above the Earth's surface,
NASA和美国空军对太空的定义也是距离地球表面80公里以外的区域，
and those who cross that line officially become astronauts.
那些越过这条线的人就算正式成为宇航员了。
OK, so the definition of space is up in the air, but what even is the atmosphere?
言下之意，外太空的定义依然悬而未决，那大气层又是什么情况呢？
Yes, it's the bubble of gases that shield and insulate the earth from the aggressive radiation of the sun and the cold dark depths of space,
没错，它就是保护并隔离地球，让地球免受太阳的强辐射，同时不被太空深处寒冷的黑暗吞噬的气流区，
but like most complex things, it's got layers:
但和大多数复杂的东西一样，大气层也分层：
The troposphere, with all our fun weather and necessary gases for breathing and surviving;
首先是对流层，我们所有有趣的天气以及地球上的生命呼吸和生存所必需的气体都发生在这一层；
The stratosphere, where commercial airlines fly when possible because there's usually less turbulence;
接着是平流层，在可能的情况下，民航客机就是在这一层飞行，因为那里的气流通常没有那么颠簸；
the mesosphere, where most meteors burn up and the highest layer at which clouds can form;
然后是中间层，大多数流星都是在这一层燃烧的，这一层也是云能存在的最高位置；
And then comes the thermosphere, which is where that tricky Karman line lives—
接下来是热层，也就是那条棘手的卡门线所在的层——
and this is where astronauts begin to experience weightlessness, and is where the ISS orbits!
这里是宇航员开始感受到失重的地方，也是国际空间站运行轨道所在的位置！
That means that technically, our most commonly defined line of where space begins is still in Earth's atmosphere.
这就意味着，严格来讲，通常定义的外太空起点实际上仍在地球的大气层内。
And then finally, there's the exosphere,
最后是外层，
that final layer between us and outer space, made up of super spaced out hydrogen and helium atoms
也就是我们和外太空之间的最后一层，这一层的成分是超间隔的氢原子和氦原子，
slowly dissipating out to nothing up to 200,000 kilometers away from earth's surface or so we thought.
但密度会随着纬度升高减小，到海拔20万km——至少我们认为是这个高度——的地方减为零。
We actually haven't previously really known where the exosphere ends and outer space begins,
事实上，之前我们并不知道外层明确的终点兼外太空明确的起点，
we just know that those extremely sparse gases gradually fade out into a vacuum.
我们只知道那些本就极其稀薄的气体会越来越稀薄，直至完全不存在。
But a team of astronomers has recently dropped a total bombshell.
但最近，一组天文学家抛出了一枚重磅炸弹。
When the cloud of gases in the exosphere reflects the Sun's UV light, it creates a luminosity, a glow that we can see, called the geocorona.
外层的气体云反射太阳的紫外线时会发出光芒，一种我们能够观测到，名为“地冕”的光芒。
These new observations of the geocorona indicate that
对地冕的这些新观测表明，
the exosphere may extend up to 630,000 kilometers away from earth—a distance that includes the moon!
大气层的外层可能延伸到了距离地球63万公里的地方——这个距离就包住了月球！
So technically, the moon is in the Earth's atmosphere!
所以，严格来讲，月球也在地球的大气层里！
This realization is thanks to an instrument called the Solar Wind Anisotropies Instrument, or SWAN.
这一发现要归功于一种叫做太阳风各向异性仪(SWAN)的仪器。
SWAN was able to measure and analyze the full extent of the geocorona, making us think about our atmosphere in a whole new way.
SWAN能测量并分析出地冕的外围边界，帮助我们用一种全新的方式来认识大气层。
See, sunlight interacts with the hydrogen atoms of the exosphere at a wavelength called Lyman-alpha radiation,
要知道，太阳光能够和大气层外层的氢原子相撞，产生所谓的“莱曼-阿尔法辐射”，
which is something astrophysicists can measure when looking at cosmological structures in deep space.
这是天体物理学家在研究宇宙深层结构时能测量到的一种辐射。
Observing Lyman alpha radiation can tell us about the distribution of matter in space, and help us think about how the universe expanded.
观察莱曼阿尔法辐射可以得出外太空的物质分布情况，帮助我们理解宇宙膨胀的原理。
It's also a wave length that's absorbed by the inner layers of our atmosphere, so we can't see it from Earth.
这种波长的波也能被大气层内层吸收，所以我们并不能从地球上直接看到它。
But from SWAN's position in space, it was able to see and measure both--and it extended far beyond what we were expecting.
但从太空中的SWAN上能够同时看到两者——其范围还远远超出了我们的预期。
So while this discovery is remarkable in many ways,
虽然这个发现从很多方面来看都非常了不起，
not the least of which is that technically no one has ever left earth's atmosphere—
其中很重要的一方面就是，严格来讲，目前并没有人离开过地球的大气层——
it won't change space travel for us in most practical ways.
但它并不会在最实际的层面上改变我们探索太空的进程。
It's far more important for informing the future of our observations of space.
其重要性主要体现在它对我们未来的太空观测的意义上。
The new results also show that sunlight compresses the hydrogen atoms of the exosphere,
这一新发现还表明，阳光会压缩外层的氢原子，
producing pockets of denser geocorona, with the corresponding Lyman alpha radiation, depending on the sun's position.
根据太阳的位置，产生密度更大，具有相应莱曼阿尔法辐射的地冕。
So space telescopes that make measurements from within the confines of the exosphere
所以，观察夜空时，在大气层外层范围内进行测量的太空望远镜
will need to take a new Lyman-alpha baseline level--and the bunching of the geocorona--
还需要考虑新的莱曼-阿尔法基准——和聚束的地冕——
into account when observing the night sky, hopefully letting us peer further, and with greater accuracy.
这样兴许能让我们看得更远，更准确。
One last amazing thing about this piece of information is that this isn't even new research—
还有另一个非常棒的地方，那就是这一发现并不是什么新研究成果——
these observations were made by SWAN in the late 90's, and were only JUST dug out of the archives for further analysis!!
而是SWAN在90年代末就得出了的发现，只是科学家们最近才为了进一步分析才从档案把他们翻了出来！！
What other startling discoveries could be lurking in a cupboard somewhere?
那些犄角旮旯里还会潜藏着哪些惊人的发现呢？
Make sure to subscribe for all your space updates, like this video here.
记得订阅，获取所有有关太空的更新内容，比如这个视频。
Thanks so much for watching and I'll see you next time on Seeker.
感谢大家的收看，我们下期再见！
