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Comet C/2022 E3 (ZTF) makes its way through the solar system. To the naked eye, the comet won't look as green as this picture. This image is normally achieved by a camera taking a long exposure.
彗星C/2022 E3 (ZTF)正在穿越太阳系。用肉眼看，彗星不会像这张照片那么绿。这种图像通常是由照相机长时间曝光得到的。
One thing astronomers have become increasingly aware of in the past few decades is how many objects are part of our one special solar system. Whereas we once understood our system as composed of a sun, some planets and an asteroid belt, we now know there are millions of objects beyond the orbit of Neptune in the Kuiper Belt — and there's more left to discover (Planet X, anyone?).
在过去的几十年里，天文学家越来越意识到有很多天体是我们这个特殊的太阳系的一部分。虽然我们曾经认为我们的系统是由一个太阳、一些行星和一个小行星带组成的，但我们现在知道，在柯伊伯带的海王星轨道之外还有数百万个物体——还有更多的物体有待发现(行星X，有人吗?)
Some of these distant objects occasionally make a visit to the inner parts of the solar system, including comets on long orbits traveling billions of miles over tens of thousands of years. One such comet has been making headlines recently for its distinctive green hue — but what causes a comet to appear a certain color in the first place?
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其中一些遥远的天体偶尔会造访太阳系的内部部分，包括在长轨道上运行的彗星，它们在数万年的时间里运行了数十亿英里。最近，一颗这样的彗星因其独特的绿色色调而成为头条新闻——但是什么导致彗星最初呈现出某种颜色呢?
Contents 目录
Meet Comet C/2022 E3 (ZTF) 遇见彗星C/2022 E3 (ZTF)
What Makes Comets Green? 是什么让彗星变绿?
How Common Are Green Comets? 绿色彗星有多常见?
Meet Comet C/2022 E3 (ZTF)
Comet C/2022 E3 (ZTF) is shown in the night sky. It's expected to be unusually bright and may just be visible to the naked eye.
彗星C/2022 E3 (ZTF)出现在夜空中。预计它会异常明亮，可能只能用肉眼看到。
Originating in the far outer reaches of the solar system in an area called the Kuiper Belt, Comet C/2022 E3 (ZTF) was discovered in March 2022 at the Zwicky Transient Facility in California — hence the parenthetical part of its name. It is expected to be nearest to Earth on Feb. 1 at 1:11 p.m. EST and may be visible to the naked eye.
彗星C/2022 E3 (ZTF)起源于太阳系遥远的柯伊伯带，于2022年3月在加利福尼亚州的兹威基瞬态设施被发现——因此它的名字是插入部分。预计它将在美国东部时间2月1日下午1点11分距离地球最近，肉眼可能可以看到。
Astronomers estimate that the last time C/2022 E3 (ZTF) was visible was during the time that Neanderthals were alive and a major ice age covered most of the land on Earth with huge glaciers (the comet has a 50,000-year orbit). Today, the world is obviously much different, but the awe caused by the appearance of this cosmic visitor remains much the same.
天文学家估计，C/2022 E3 (ZTF)最后一次可见是在尼安德特人活着的时候，一个大的冰河期用巨大的冰川覆盖了地球上的大部分土地(彗星的轨道是5万年)。今天，世界显然已经大不相同了，但这个宇宙访客的出现所引起的敬畏却几乎没有改变。
In addition to its long orbital period, another trait that makes C/2022 E3 (ZTF) special is its color. The coma, the glowing atmosphere around the comet's head or nucleus, has high concentrations of diatomic carbon and cyanogen (made of bonded carbon and nitrogen). As this compound is illuminated by the sun, it glows green in the visible light spectrum. This is why many articles about C/2022 E3 (ZTF) have called it the "green comet.除了轨道周期长，C/2022 E3 (ZTF)的另一个特点是它的颜色。彗发，即彗星头部或彗核周围的发光大气，含有高浓度的双原子碳和氰(由碳和氮结合而成)。当这种化合物被太阳照射时，它在可见光光谱中发出绿色的光。这就是为什么许多关于C/2022 E3 (ZTF)的文章称它为“绿色彗星”。
What Makes Comets Green? 是什么让彗星变绿?
The parts of a comet include the coma, the head (nucleus) and two tails: the dust tail and the ion or gas tail.
彗星的组成部分包括彗发、彗头(彗核)和两条彗尾:尘埃彗尾和离子或气体彗尾。
As suggested by the composition of Comet C/2022 E3 (ZTF), different elements in a comet can contribute to the green hue it appears to have for Earthly observers.
正如彗星C/2022 E3 (ZTF)的组成所表明的那样，彗星中的不同元素可以导致地球上的观察者看到它的绿色。
The coma of a comet doesn't actually form until somewhere around the orbit of Mars, where a comet's proximity to the sun causes ice on the rocky body to melt and create an atmosphere-like halo of dust and gas surrounding the comet. As the coma (and comet) move closer to the sun, the gases in the coma go through atomic transitions due to the effect of sunlight.
彗星的彗发实际上是在火星轨道附近的某个地方才形成的，在那里，彗星接近太阳导致岩石体上的冰融化，并在彗星周围形成由尘埃和气体组成的类似大气的光环。当彗发(和彗星)靠近太阳时，彗发中的气体在阳光的作用下会发生原子跃迁。
In the case of C/2022 E3 (ZTF), sunlight shining on the comet is splitting the diatomic carbon molecules in its tiny coma atmosphere into single carbon atoms; this is what produces the green hue around the comet's nucleus or head. The comet's dust tail will still appear to be white, and its fainter gas tail will appear bluish.
以C/2022 E3 (ZTF)为例，照射在彗星上的阳光正在将其微小的彗发大气中的双原子碳分子分裂成单个碳原子;这就是为什么彗星的核心或头部周围会出现绿色色调。彗星的尘埃尾巴仍然是白色的，而它微弱的气体尾巴则是蓝色的。
There have been other particularly green comets in recent years, including C/2007 N3 Lulin, C/2014 Q2 Lovejoy and C/2021 A1 Leonard, due to the same effect. Comets can also take on slightly different colors, including teal and blue, based on the chemical composition of the gases in the coma that forms around them. Some comets can even be red.
由于同样的效应，近年来还有其他特别绿的彗星，包括C/2007 N3 Lulin, C/2014 Q2 Lovejoy和C/2021 A1 Leonard。彗星的颜色也会略有不同，包括蓝绿色和蓝色，这取决于彗星周围形成的彗发中气体的化学成分。有些彗星甚至是红色的。
How Common Are Green Comets? 绿色彗星有多常见?
While you might have seen headlines referring to Comet C/2022 E3 (ZTF) as a "rare green" comet, these are actually two different descriptors and should be separated by a comma (not a coma)!
虽然你可能看过标题称彗星C/2022 E3 (ZTF)为“罕见的绿色”彗星，但这实际上是两个不同的描述符，应该用逗号分隔(不是昏迷符)!
C/2022 E3 (ZTF) is green, certainly, but it is also rare — its rarity comes from the fact that it has that 50,000-year orbit through our solar system. Scientists believe that there have been well over a thousand generations since this comet might have been spotted by our distant
homo sapiens
ancestors. And computations suggest it may never be seen again.
C/2022 E3 (ZTF)当然是绿色的，但它也很罕见——它的罕见之处在于它在太阳系中有长达5万年的轨道。科学家们相信，自从这颗彗星可能被我们遥远的智人祖先发现以来，已经有一千多代人了。计算表明，它可能永远不会再出现。
For comets in general, appearing green as they approach the sun and pass by Earth is not uncommon; there were several recent green comets mentioned already, and we may well get to see more during our lifetimes. It all comes down to the chemical composition and how much diatomic carbon and cyanogen each one contains — something that was determined long ago during the Big Bang and formation of our solar system.
一般来说，彗星在接近太阳并经过地球时呈现绿色并不罕见;最近已经提到了几颗绿色彗星，在我们的有生之年，我们很可能会看到更多。这一切都归结于化学成分，以及它们各自含有多少双原子碳和氰——这是很久以前在大爆炸和太阳系形成期间确定的。
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