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When you look up at the night sky, it's easy to think that all the stars up there are basically the same.
仰望星空时，我们很容易产生所有星星都一模一样的感觉。
After all, for the most part, they do all look alike from your point of view.
毕竟，从我们的角度看，星星彼此间长得很想象。
But get this: Some of the brightest, most easily visible stars in the sky also happen to be among the most important to astronomy.
但这里要告诉大家的是：天空里更容易看到的星星对于天文学的意义也更为重要。
You've been looking at some really weird stars, and you didn't even know it!
有一些肉眼可见的恒星十分怪异，我们对它们可以说是一无所知！
Here are three of them.
举三个例子吧。
First, take the Big Dipper.
先说北斗七星。
It's visible in most parts of the world, and it's made up of four stars in the "cup" and three in the "handle."
世界上的大多数地方都看得到它，它是由4颗恒星组成的杯子和3颗恒星组成的把手。
But if you look at them really closely, they're not all what they seem.
但仔细观察后会发现根本不是如此。
Next time you're outside, take a peek at the middle star in the handle.
下次在户外的时候，大家可以瞥一眼把手里中间的那颗恒星。
Look closely, and you'll see that it's actually two stars, called Mizar and Alcor.
离近点看，会发现其实是两颗星，即开阳星和辅星。
The pair is about 80 light-years away, and we've known about it for thousands of years.
这两颗星离地球有近80光年的距离，数千年前，我们就已经知道了它们的存在。
In fact, they probably represent the first known binary stars: stars that orbit one another.
实际上，它们很可能是人类所知的第一对双子星：围绕彼此运转的恒星。
But that's not where the fun stops.
但故事到这里还没有结束。
If you point a small telescope at Mizar, you'll see that it isn't just one star, either.
如果用小型望远镜观测开阳星，就会发现其实它也算不上是一颗恒星。
It's also a binary, with two stars now called Mizar A and B.
开阳星其实也是一对双子星，两颗星分别是开阳AB双星。
In 1617, it became the first known telescopic binary, or a pair of stars orbiting each other so closely that you need a telescope to split them.
1617年，开阳星是第一颗通过望远镜观测到的双子星。组成双子星的两颗恒星彼此紧密环绕，所以要通过望远镜才能将它们区分开来。
Then, in 1890, we found even more stars.
1890年，我们又发现了更多的恒星。
The use of a new tool called a spectrograph, which measures light patterns, revealed that Mizar A was itself a binary.
新工具光谱仪通过测量光带发现，开阳A星本身又是一颗双子星。
In fact, in the years since, we've actually realized that Mizar A, B, and Alcor are all binary stars.
实际上，在那以后的数年中，我们发现，开阳AB星以及辅星都是双子星。
So what looks like one star in the handle of the Big Dipper is actually an intricate sextuple star system!
但北斗七星的把手里貌似是一颗恒星的星其实是复杂的六星体系。
It's binaries all the way down.
从头缕下来有好多双子星。
The Big Dipper is one of the most common and well-known figures in the sky, but it's also an easy reminder that everything isn't always what it seems.
北斗七星是最常见也是最出名的天空"明星"，对于它的新发现也提醒着我们，事情并不总是表面上看起来那么简单。
Sometimes, it's a lot cooler.
有时候，真相比表象酷多了。
During summer in the northern hemisphere, there's another weird star you can spot.
北半球夏季的时候，还能看到另一颗不同寻常的恒星。
Just look straight up.
只要抬头就能看见。
Even in light-polluted skies, you should be able to see an enormous trio of stars called the summer triangle.
即便在阳光明媚的天空里，也能看到三颗星组成的巨大集团，名作夏季大三角。
The brightest of those three stars is Vega, and it's long been one of the key reference stars in astronomy.
三颗星中最亮的一颗叫织女星。很长时间以来，织女星一直都是天文学里重要的角色。
Among other things, astronomy's magnitude system for describing brightness was anchored by Vega, the so-called magnitude-zero star, for decades.
几十年来，天文学一直以织女星为标准来衡量恒星的亮度，假定它的亮度为0。
But here's the thing: Vega might not have been the world's best choice for a standard star.
但要向大家说清楚的是，织女星可能并不是最好的选择。
Normally, stars are actually pretty simple things, and every one of a given type should have roughly the same size and brightness.
正常情况下，恒星都遵循简单的规律，每一种既定类型的恒星，大小和亮度都差不多。
Except for Vega. It seems to be a lot brighter than its type would suggest.
但织女星除外，因为织女星要比其所属类别的恒星亮一些。
And over the last couple of decades, astronomers have finally figured out why.
过去几十年里，天文学家一直试图找到其中的原委。
The fact that stars should follow patterns like these hinges on a critical assumption:
之所以说恒星是有规律的，是基于一个关键的假设：
that they're all basically spheres.
它们都是球体。
And this makes sense. In the simplest sense, stars are just big collections of hot gas.
这一点说得通。以最简单的角度来看恒星：它们这是大量高温气体的集合。
All that hot gas wants to spread out as much as possible, but gravity is constantly tugging it back together.
这些高温气体想要向外扩散，但引力将它们聚集到了一起。
And since gravity pulls with the same strength in every direction, voila, a sphere.
而由于引力在各个方向上的力度都是相同的，所以就形成了球体。
But Vega is an exception.
但织女星是个例外。
It turns out that this star is spinning really, really quickly, something like 70-90% of its breakup speed.
织女星的转速非常非常快，已经达到了分解速度的70%-90%。
And just like when you're riding a rollercoaster, that spinning causes an apparent force that counteracts gravity.
跟坐过山车同理，织女星在高速旋转过程中形成的一股力可以与引力相抵消。
Since the equator spins faster than the poles, gravity is weakest there, and Vega bulges out.
而由于赤道比两极的转速更快，引力又最弱，所以织女星就凸了出来。
This isn't a subtle effect, either: Its radius is 19% larger at its equator than the pole.
这种差别带来的影响可不小：赤道的半径比两极大19%。
It looks so bright to us on Earth because, through random chance, our view looks at Vega's pole, meaning we're seeing the largest possible cross-section of the star.
身处于地球上的我们看织女星之所以如此明亮是因为：有时候，不经意间，我们看到织女星的两极，也就是织女星的横截面。
And with the maximum amount of area emitting light towards us, it's no surprise that Vega seems brighter than it should be.
横截面向我们发射最多的光，所以织女星看起来更亮也就不奇怪了。
And, finally, Vega's got some brightness troubles, but no star in the sky has it worse than Mira.
最后要说的是，织女星在亮度方面有自己的难题，但就亮度方面而言，问题最严重的要属薴藁增二了。
Like the stars in the Mizar system, this one is also a binary pair.
与开阳系统中的恒星相似，薴藁增二也是一颗双子星。
It's made of Mira A, a huge, red giant, and Mira B, a little white dwarf.
它是由红巨星薴藁增二A和小型的白色矮星薴藁增二B组成。
You can't spot Mira B with the naked eye, but you can see the red giant in the constellation Cetus.
肉眼是看不到薴藁增二B的，但可以看到鲸鱼座中的薴藁增二A。
It's visible from basically anywhere on Earth, but it's best seen near the end of the year.
基本上，地球上的任何地方都看得到薴藁增二A，临近年终的时候看得最为清晰。
Well, when you can see it at all, that is.
能看得一清二楚的时候，就是最好的时机了。
Some days, it's one of the brightest stars in the night sky; other times, it's so dim you can't see it without a telescope.
它时而是夜空中最亮的星，时而暗淡得通过望远镜也看不到。
And that is a sure-fire sign something weird is going on.
这预示着有怪异的现象发生了。
Mira A, usually just called Mira, is probably the earliest-known example of a variable star, or one whose brightness changes substantially back and forth over time.
薴藁增二A通常也叫薴藁增二，很可能是我们最早了解到的一颗变星。所谓变星就是亮度会发生变化的星体。
This happens because of big swings in the star's temperature and even its size.
之所以会有这种情况是因为薴藁增二的温度甚至大小都有很大的浮动区间。
Today, we know of a few kinds of variable stars, including other red giants, and we generally understand how they work.
今天的我们对一些种类的变星有一定的了解，包括其他红巨星。我们基本上知道他们是如何运作的。
But we just can't figure out Mira.
但对于薴藁增二，我们一无所知。
See, stars enter the red giant phase after exhausting the hydrogen fuel in their cores and starting to burn heavier elements like helium.
可以确定的是：恒星在燃尽内核的氢燃料之后就会进入红巨星时期，并开始燃烧质量更大的元素，比如氦。
Helium burning isn't nearly as steady, so in other kinds of variable stars, it sort of sputters and causes the star to brighten and dim.
氦元素的燃烧不如氢燃烧稳定，所以燃烧的时而冷淡，时而浓烈，也就使整颗恒星忽暗忽亮的。
But that doesn't seem to be the whole story with Mira's big swings.
但薴藁增二的亮度变化也不只限于这一个原因。
Instead, its variation probably has to do with convection, the process that transfers heat from a star's core to its surface.
还有一个原因是对流。对流可以将热量从恒星内核传播到表面。
For instance, if the amount of heat being transported outward was changing over time, that would result in the star shining with different brightnesses.
比如，如果向外传播的热量会随着时间发生改变，那么恒星的亮度也会发生变化。
But we're still figuring it out. One thing is sure, though: Mira isn't alone in this.
关于对流的问题，我们还在研究。但有一件事是确定的：薴藁增二并不是唯一一个亮度不稳定的星体。
We know of hundreds of so-called "Miras," most of which are just too far away to be easily seen.
跟薴藁增二类似的双子星还有上百个，其中，大多数都太远了，很难观测到。
But if you're lucky, you can spot the first one with the naked eye.
但如果足够幸运的话，也能用肉眼看见第一颗。
Oh, and as a bonus? You won't be able to see it without a fancy ultraviolet telescope, but researchers also discovered in 2007 that Mira has a tail!
哦？有福利了么？虽然用炫酷的紫外望远镜看不到，但研究人员在2007年发现薴藁增二有一条尾巴！
It's a whopping 13 light-years long, and it's made of elements like carbon and oxygen being shed by the star as it zooms through space.
这条有13光年长，其穿越宇宙的时候，会流散出碳元素和氧元素。
Just in case this object wasn't already weird enough.
说这个，只是想渲染它的不走寻常路。
Some days, modern astronomy can feel remote and unknowable, because a lot of the discoveries we make happen light-years away or on time scales too large to comprehend.
有的时候，现代天文学也有一眼望不到头的无尽未知感，因为我们的很多发现，不是距离我们都有很多光年的距离，就是时标太大导致无法理解。
But there's a lot visible from your own backyard, too.
但我们自己的后花园里也有很多可以观测惊奇有待探寻。
So, sometime, go outside and look up!
所以有时候还是要到外面去看看！
You might just be looking at something really incredible.
说不定就会看到不可思议的景象呢。
Thanks for watching this episode of SciShow Space!
感谢收看本期的《太空科学秀》！
While you're out stargazing, you might also notice another object in the sky: the moon.
"夜观星象"的时候，或许还会看到天空中的月亮。
Sometimes, it looks way bigger on the horizon than it should, and it's all thanks to a cool optical illusion.
有时候，地平线上的月亮看起来要比它本身大，这是因为视错觉在起作用。
You can learn all about it in another one of our episodes.
关于视错觉，我们在另一集里有讲解。
