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It's not often that the whole world is talking about astronomy.
全世界都在谈论天文学并不常见。
A lot of the time, it's just space nerds like us.
许多时候，只有像我们这样的太空迷才会谈论它。
But a solar eclipse, especially one that travels across the entire face of the United states, is definitely going to do it.
但一次日食，而且是覆盖全美的日食，绝对值得讨论。
Just one month from now, on August 21, the United States will experience its first total solar eclipse since 1979.
一个月后，也就是8月21日，美国将会经历1979年后的首次日全食。
So for a lot of people, including me, this will be your first opportunity to see one without having to leave the country.
所以包括我在内的许多人，不用离国就有机会首次看到日全食。
People are calling it the Great American Eclipse, since the path of the total solar eclipse only passes through the US, and cuts all the way across the contiguous 48 States.
人们称它为“Great American Eclipse”（伟大的美国日食），这是因为日全食只在美国出现，并一直贯穿48个大州。
Over the last couple of centuries, solar eclipses have taught scientists a lot about the sun and about the way the universe works in general.
在过去的几个世纪里，日食告诉科学家们许多与太阳和宇宙一般运转方式有关的知识。
But you don't need to be a scientist to be captivated by watching the sun just suddenly go dark in the middle of the day.
白天突然变黑，即使你不是科学家，也会对这种现象感到好奇。
If you want to experience this eclipse for yourself, you just have to be in the right place at the right time.
如果你想亲自体验这次日食，你必须在正确的时间出现在合适的地点。
A solar eclipse happens when the moon goes between the Earth and the sun, casting a shadow across the Earth's surface.
日食发生时，月球在地球和太阳之间，在地球表面投射阴影。
From our perspective, it looks like the sun is being blocked out.
从我们的角度看，太阳看起来像是被遮住了。
A total solar eclipse happens when this arrangement is perfect:
当这种排列完美时，就会发生日全食：
the moon is directly between the Earth and sun, and it's close enough to Earth to completely block out the sun for a short time.
月球恰好在地球和太阳之间，它离地球很近，可以在短时间内完全遮住太阳。
That's exciting for anyone to watch, but for scientists, it's also incredibly useful.
任何人看到日全食都会兴奋，但对科学家来说，它也相当有用。
When the moon covers the sun, we can see the sun's corona, the layer of gas that surrounds the sun.
当月球遮住太阳时，我们能看到日冕，它是太阳周边的大气层。
Normally, it's a lot harder to separate what's happening in the corona from what's happening with the rest of the sun.
正常情况下，人们很难将日冕的情况和太阳其余部分的情况分开来看。
Because the sun is pretty bright...
因为太阳太亮了...
By studying the corona during eclipses, researchers have learned a lot about what it's made of, how it works, and even its surprisingly high temperature.
研究人员在日食期间研究日冕，了解到许多知识，包括它的构成、工作方式及其惊人的高温。
The temperature discovery happened during the 1879 eclipse, when we found what we thought was a brand new element.
温度的发现是在1879年的日食期间，当时我们还认为它是一种全新的元素。
Turns out, it was just super hot gaseous iron.
但事实证明，它只是超级热的气态铁。
For iron to be a gas, that meant the corona must have been way hotter than the sun's surface, like, millions of degrees hotter.
铁成气态，这意味着日冕的温度必须比太阳表面高很多，得高出数百万度。
That was totally unexpected, and almost 150 years later, we still don't know why the corona is so hot.
这完全出乎意料，近150年过去了，我们仍然不知道为什么日冕会这么热。
We're launching a probe next year to help figure it out.
我们明年将启动一项调查，来帮助解决这个问题。
But probably the most important thing we ever learned from an eclipse was in 1919,
但也许我们从日食中获悉的最重要东西是在1919年，
when a total solar eclipse over south America and Africa provided the first proof of Einstein's general theory of relativity.
覆盖南美和非洲的日全食为爱因斯坦的广义相对论提供了第一份证据。
One of Einstein's greatest predictions was that gravity can bend light,
爱因斯坦的一个伟大预言是重力能使光线弯折，
and the sun has a strong enough gravitational pull that it should bend the light from the stars just behind it,
太阳有足够强的引力，它应该能使背后恒星发出的光弯折，
shifting their position a little in the sky from our perspective here on Earth.
从地球人的角度来看，恒星在天空中的位置稍微移动了些。
But normally, of course, you can't see the stars next to the sun in the sky, because the sun is very bright.
但正常情况下，因为太阳非常亮，你看不到天空中太阳周围的恒星。
So scientists couldn't check if it was actually bending starlight until the 1919 eclipse, while the sun was dark enough to see the stars around it.
所以，科学家也不能验证引力是否真能使星光弯折，直到1919年的日食爆发，太阳足够暗才看到它周围的恒星。
By measuring the positions of stars right next to the eclipse, they found that the light from the stars was being bent by the sun's gravity.
通过测量恒星在日食附近的位置，他们发现星光被太阳引力弯折。
Even better: the positions of the stars perfectly fit with Einstein's equations.
更好的结果是：恒星的位置完美契合爱因斯坦方程。
And that's how the moon moving in front of the sun almost a century ago proved the theory that we still use to describe a lot of the universe.
近一个世纪前，日食现象证明了这个理论，我们仍用它来描述许多宇宙现象。
So there are plenty of reasons for humans to be interested in eclipses just from a scientific perspective.
因此，仅从科学的角度来看，人类有很多理由对日食感兴趣。
But also...they're just really freakin' cool.
而且…他们真的很酷！
If you want to see this eclipse for yourself, you'll first have to get to a place where it'll be visible.
如果你想亲眼看到这次日食，你要先到一个可以看到它的地方。
You'll be able to see the partial eclipse where a smaller part of the sun is blocked out,
在加拿大、中美洲和西欧一些地区，你只能看到日偏食，即只有一小部分太阳被挡住了，
but not the whole thing from Canada, Central America, and some parts of Western Europe.
看不到日全食。
But if you want to see the total eclipse, you'll have to put yourself somewhere along that slice of the US, aka the path of totality, on August 21.
但如果你想看日全食，你就得在8月21日身处美国的某条线上，我们把这条线叫做“日全食带”。
The whole eclipse lasts about two and a half hours, although totality is no more than about two and a half minutes.
整个日食大约持续两个半小时，但全食的时间不超过2分半。
It is weird that the moon and the sun are almost exactly the same size in the sky! Just a coincidence!
天空中月球和太阳的大小几乎完全相同，真是不可思议！但这只是一个巧合！
The exact timing depends where you are, because the eclipse will move along the path of totality as the Earth rotates and the moon moves in its orbit.
准确的时机取决于你的位置，因为日食在“日全食带”中也在不断变化，地球在自转，月球也在公转。
If you're in Oregon, the whole show will start around 9 am, and if you're in South Carolina, it's more like 1pm.
如果你在俄勒冈州，日全食将从上午9点左右开始，如果你在南卡罗来纳州，时间大约是下午1点。
There's a link in the description where you can get exact details for your location.
有一个说明链接，你可以从上面获取你所在位置的详细情况。
Even if you're in the right place at the right time, you'll need still need to take some safety precautions to watch the eclipse.
即使你在正确的时间到达合适的地方，你还需要采取一些安全措施来观察日食。
Looking directly at the sun, I assume we all know this, can cause eye damage or even blindness,
我想我们都知道这一点，直视太阳会导致眼睛损伤甚至失明，
because your eyes just aren't equipped to handle that level of light intensity.
因为你的眼睛没有能力处理那种程度的光强。
And a lot of the time the damage is painless, and people don't even realize it's happening.
很多时候，伤害并不痛，人们甚至没有意识到它正在发生。
So the safest way to watch the eclipse is through something that projects the image onto something else, like a pinhole projector.
因此，观看日食最安全的方法是通过一些东西将图像投射到其他东西上，比如针孔投射器。
If you want to look at it directly, there are lots of people out there selling eclipse viewing glasses,
如果你想直接观看，很多人在卖日食观测眼镜，
but here's the thing: if they have a tiny imperfection, or aren't made to the right standards...that could be really bad.
但问题是，如果他们有微小的缺陷，或者没有达标……那可能真的很糟糕。
Because, again, you might not even realize that your eyes are being damaged.
因为，你甚至可能没有意识到你的眼睛被损坏了。
After every solar eclipse, people end up in hospitals because their vision starts to go weird, even though they didn't feel anything during the eclipse.
每次日食之后，人们都会去医院，因为他们的视力开始变得很奇怪，即使他们在日食期间没有感觉不适。
So, be careful. Make sure any viewing glasses you get meet the latest standards. A lot of them don't.
所以，千万要小心。确保你得到的任何眼镜都符合最新标准。但很多人都没有这样做。
You can watch the eclipse with the naked eye during that tiny window of totality,
你可以在极短的时间内用肉眼观看日食，
if you happen to have gotten yourself to the path of totality,
如果你恰好处于日全食带，
but you have to make sure to have the glasses back on before totality ends.
但你必须要在日全食时把眼镜戴上。
If you miss it, the good news is that you won't have to wait nearly as long the next time around:
如果你错过了这次的日食，好消息是你下次不需要等那么久了，
there'll be another total solar eclipse in north America in 2024.
在2024年，北美将会有另外一次日全食。
But if you do make it to the path of totality, and fingers crossed, it's a clear day, get ready for an incredible show.
但如果你掌握了全食的轨迹，那就祈愿那天是个晴天，准备好看一场惊人的表演吧！
If you're looking for a safe way to see the eclipse, we've got you covered with a special SciShow pinhole projector card!
如果你正在寻找一个看日食的安全方法，我们已经给你准备了一个特殊的科学秀针孔放映机卡！
All you have to do is poke a hole in the middle, grab a plain piece of paper to project the image onto,
你所要做的就是在中间戳一个洞，拿一张普通的纸来投射图像，
and adjust the distance between the card and the paper until you see a clear image of the eclipse.
调整卡片和纸张之间的距离，直到你看到一个清晰的日食图像。
The tiny hole acts like the lens in a camera, focusing the light that passes through so that you can see the image on the paper behind it.
这个小孔就像照相机的镜头一样，聚焦经过的光线，这样你就能看到它背后纸上的图像了。
You can get your SciShow pinhole projector at dftba.com/scishow!
你可以在dftba.com/scishow上得到你的科学秀针孔投影仪哦！
