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When people talk about space, it's often on scales so large they're almost incomprehensible:
人们每每提及宇宙时，总是说它浩瀚无边，无法尽数了解。
Thousands of light-years. Hundreds of millions of years. Billions of galaxies.
毕竟它有上千光年远，发展了数亿年，包含数十亿个星系。
But some of the universe's most beautiful sights are much more fleeting, like planetary nebulas, glowing, colorful shells of gas that only last for about 10,000 years or so.
但宇宙里有些最美的景象犹如昙花一现，比如行星状星云，这是一种飘逸的彩色气体云，寿命只有近1万年左右。
And this week, a paper published in Nature Astronomy reported the first one that appears to be inside out.
而就在本周，《自然天文学》上发表了一篇论文，称发现了第一个里外颠倒的行星状星云。
Despite the name, planetary nebulas have nothing to do with actual planets.
虽然叫行星状星云，但它却与行星没什么关系。
They got their name in the 1700s, when astronomers saw them as smears of light in their telescopes, not single points like stars, but disk-like objects that looked more like planets.
行星状星云得名于18世纪，那时候，在天文学家的望远镜里，行星状星云就是一团团发着光的团，但却不像恒星一样，不是单独的点，而是像圆盘一样的物体，看着像行星。
We've known they're not planets for a long time, but the name stuck.
虽然很久以前，我们就知道它们不是行星，但名字已经固定下来了。
Instead, planetary nebulas are a type of stellar remnant, or what's left over after a star dies.
其实，行星状星云是星体的残留物，是恒星结束生命周期后留下的物体。
Stars like our Sun aren't massive enough to undergo a supernova explosion, so their death throes are far less violent.
类似太阳一样的恒星质量不够大，不会发生超新星爆炸，所以死得也没那样轰轰烈烈。
The outer layers of the star, or stellar envelope, are shed into interstellar space, and the core collapses into a super dense white dwarf.
这种恒星的外层，也就是恒星包层，会流逸到星际之中，而内核会汇入密度超大的白矮星中。
The electromagnetic radiation emitted from that core reacts with the particles from the envelope and other matter in the area.
内核释放出的电磁辐射会与恒星包层中的粒子以及该其区域的其他物质发生反应。
Sometimes those particles absorb the energy and reemit it at other wavelengths, producing a rainbow of colors.
有时候，这些粒子会吸收能量，并以其他波长再次释放出去，产生多彩的彩虹。
Other times, the photons of light emitted from the white dwarf are so energetic they knock electrons off their parent atoms entirely, creating charged ions.
有时候，白矮星释放的光量子由于携带巨大能量，会将电子撞离自己的原子，产生带电离子。
Normally, the stuff closer to the white dwarf is more ionized than the stuff farther away, because it gets hit with the most radiation.
正常情况下，离白矮星越近的物质，电离程度越大，因为这样的物质受电磁辐射的撞击最大。
But this planetary nebula is the first one we've seen that has it the other way around, and astronomers think that's because the inner shell is excited by shocks from what's known as a “born again” event.
但行星状星云却别具一格，对此，天文学家认为，这是因为它的内壳因“重生”过程的撞击而活跃起来。
Basically, the stellar remnant at the center, imaginatively named IRAS 17514-1555, underwent a sort of thermal pulse and its nuclear engine fired up again, expanding the star from a white dwarf back into a red giant.
基本情况如下：中央的行星状星云（也就是IRAS 17514-1555），它经历了类似热脉冲的过程，就像再次点燃了核发动机，使它从一颗白矮星变成了红巨星。
Yeah. It's an undead star.
没错，它已经成了不死之星。
This isn't the first “born again” event we've ever seen.
这种过程也不是我们第一次见的“重生”过程了。
For example, there's also Sakurai's Object, which was discovered back in 1996 in the area of the sky near the constellation Sagittarius.
比如，1996年在人马座星群附近发现的樱井之星。
But this is the first time we've seen one with an inside-out nebula, and the researchers think it's happening as the star in its center rapidly cools back down from its second shot at life, whereas Sakurai's Object is still heating up.
但这是我们第一次见到星云内外颠倒，对此，研究人员认为这种现象发生的条件是：星云内部的恒星在第二次活跃后迅速冷却，而樱井之星却是在持续升温的。
In the past 4 decades, IRAS 17514's brightness has dropped by a factor of 10,000, and in the process, it's been ejecting large amounts of carbon-rich material at speeds faster than the nebula is expanding.
过去40年来，IRAS 17514的亮度衰减了1万倍，在这个过程中，它释放了大量富含碳的物质，速度远超过了星云扩张的速度。
That creates a shockwave in the nebula, which heats up the material just in front of it enough to ionize atoms that usually wouldn't be.
这就使星云产生了冲击波，导致星云前方的高碳物质极度升温，从而使一般情况下不会发生电离的原子发生电离。
Meanwhile, less-ionized particles are left in its wake.
与此同时，电离程度弱一些的粒子尾随其后。
That leads to more highly-ionized material outside of the less-ionized stuff; in other words, an inside-out nebula.
这就使得电离程度稍弱物质之外产生了高度电离的物质，也就是说，星云内外颠倒发生了。
But besides being a totally unique object in the astronomy books, this planetary nebula can teach us a lot.
不过，除了是天文史上独一份儿的物体之外，行星状星云还教会了我们很多。
For one, it's a missing piece of the story of how low-mass stars turn into metal-rich white dwarfs surrounded by planetary nebulas.
比如，行星状星云涉及到低质量恒星变为金属含量高的白矮星，而且这样的白矮星周围还都是行星状星云。
And according to models, the star that became IRAS 17514 had a mass only 10% larger than our own Sun.
一些模型显示，IRAS 17514的原始恒星，其质量只比太阳多10%。
So we might be looking at what could happen in our own solar system in billions of years.
所以，IRAS 17514可能就是数十亿年后太阳系的前车之鉴。
We'll never know for certain, ‘cause we'll all be dead by then, but it's sometimes good just to know, you know?
不过这一点我们还无法确定，毕竟那时候，人类已经不复存在，但知识多了不压身。
In the meantime, there's another beautiful astronomical sight you can catch this very weekend: The Perseid meteor shower.
还有一个特例是本周末就能捕捉到的美丽天文学景象——英仙座流星雨。
It's caused by the comet 109P/Swift-Tuttle, which last passed by Earth in 1992 on its way around the Sun.
英仙座流星雨是由塔特尔彗星109P引起的，这颗彗星上一次经过地球是在1992年，当时它以太阳为环绕对象。
The comet was actually discovered back in 1862, by Lewis Swift and Horace Tuttle, but since one orbit takes over a hundred years to complete, we didn't have enough data to predict when exactly it would come around again.
首次发现这颗彗星是在1862年，由路易斯·斯威夫特和贺拉斯·塔特尔发现。但由于它公转一圈需要100多年，所以，我们还没有足够的数据来预测它什么时候会再次经过。
But each time Swift-Tuttle does, it leaves a trail of dust in Earth's orbit.
但每次塔特尔彗星经过的时候，都会在地球的轨道上留下一串灰尘。
Every year, our planet crashes into that trail and some of the tiny pieces of space debris rain down.
每年，地球都会与这一串灰尘尾巴摩擦，这时候，宇宙里的一些残骸会如雨般落下。
But they do not make it very far.
不过，涵盖路径并不远。
They strike the Earth's atmosphere at 59 kilometers per second and get burned away pretty quickly, creating a meteor shower.
这些残骸会以59km/s的速度撞击地球大气层，过程中会迅速燃烧，并产生流星雨。
Meteor showers get their names from where they appear to come from in the sky.
流星雨的名字从其降落方向而来。
We see Swift-Tuttle's remnants coming from the constellation Perseus, so it gets the name the “Perseids.”
我们看到塔特尔彗星留下英仙座残骸落下，所以给它起名为英仙座流星雨。
The Earth has lots of regularly occurring meteor showers throughout the year.
每年，地球上都可以看到一些定期发生的流星雨。
But since this one happens in August, when the evening weather is nicer, at least in the Northern Hemisphere, the Perseids is one of the more popular.
但自从英仙座流星雨（至少北半球能看到，发生的当天晚上，天气更好些）于8月发生后， 英仙座流星雨就成了最受欢迎的一个。
This year, we entered Swift-Tuttle's dust trail back on July 17th, and won't leave until August 24th, but we'll be entering the densest area on August 12th.
今年7月17日，地球再次步塔特尔彗星灰尘轨道的后尘，这一次要到8月24日才能结束。不过，我们8月12日的时候才会进入尘土量最大的区域。
So this weekend, you can expect to see about one meteor per minute.
所以本周末，每分钟都可以看到流星哦。
Assuming you don't have any clouds raining on your parade, you'll be able to see meteors streaking across all parts of the sky in the Northern Hemisphere.
如果不下雨的话，就能看到北半球漫天的流星雨了。
But they will be more visible in areas with less light pollution.
不过，光污染没那么严重的地方，看的才更清楚哦。
And lucky for all of us, one major source of light pollution, the Moon, won't be visible, since it's a new moon on Saturday.
幸运的是，主要的一个光污染源，也就是月球，在周六的时候没那么明显，因为周六是新月。
So if you can find the time this weekend, check out what the universe has to offer!
所以，如果本周末有时间的话，不妨看看流星雨吧！
Thanks for watching this episode of SciShow Space News!
感谢收看本期的《太空科学秀》！
To keep up with the latest discoveries and learn about some of the most fascinating things in the universe, just go to youtube.com/scishowspace and subscribe.
如果想持续跟进最新的发现，并了解宇宙里最好玩儿的现象，就请订阅youtube.com/scishowspace吧。
Also, if you want to celebrate your love of space with posters on your walls or shirts on your torso, check out DFTBA.com/SciShow.
如果您想在墙上、T恤上展现您对太空热爱的话，可以去DFTBA.com/SciShow看看哦。
