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A green comet will appear again in Earth's sky for the first time in 50,000 years.
一颗绿色彗星将再次出现在地球的天空，这是5万年来的第一次。
The American space agency NASA says the comet's last visit came during Neanderthal times.
美国航空航天局表示，这颗彗星上一次造访地球是在尼安德特人生活的时代。
It will come within 42 million kilometers of Earth on Wednesday before continuing on its path, unlikely to return for millions of years.
它将于周三到达距离地球不到4200万公里的地方，然后继续前进，在数百万年内不太可能返回。
Discovered less than a year ago, this green comet can be observed in the northern night sky with devices such as binoculars and telescopes.
这颗绿色彗星在不到一年前被发现，可以用双筒望远镜和望远镜等设备在北方夜空中观测到。
It is also possible to see with one's own eyes in the darkest corners of the Northern Hemisphere.
人们也可以在北半球最黑暗的角落用肉眼看到。
The comet will be best seen in the early morning hours.
这颗彗星的最佳观测时间是清晨。
It is expected to brighten as it comes closer and rises higher over the horizon through the end of January.
预计到1月底，随着它越来越靠近地球，在地平线上上升得越来越高，它会变得越来越亮。
By February 10, the comet will be near Mars.
到2月10日，这颗彗星将靠近火星。
Viewers in the Southern Hemisphere will have to wait until next month to see it.
南半球的观测者要等到下个月才能看到它。
Paul Chodas is director of the Center for Near Earth Object Studies at NASA's Jet Propulsion Laboratory in California.
保罗·乔达斯是加州美国航空航天局喷气推进实验室近地天体研究中心主任。
Chodas said that while several comets have appeared in the sky over the past year, "this one seems probably a little bit bigger and therefore a little bit brighter and it's coming a little bit closer to the Earth's orbit."
乔达斯说，虽然在过去一年里，天空中出现了几颗彗星，但“这颗彗星看起来可能更大一些，因此也更亮一点，它离地球轨道更近一些。”
The comet was discovered last March by researchers using the Zwicky Transient Facility, a special camera at Caltech's Palomar Observatory.
这颗彗星是去年3月由研究人员利用加州理工学院帕洛玛天文台的兹威基瞬变设施发现的。
That explains its official, difficult name: comet C/2022 E3 (ZTF).
这就解释了它的官方名称：C/2022 E3(ZTF)彗星。
On Wednesday, the comet will pass between the orbits of Earth and Mars at a relative speed of 207,000 kilometers.
周三，这颗彗星将以20.7万公里的相对速度通过地球和火星之间的轨道。
Its nucleus, or center, is thought to be about 1.6 kilometers across, with its tails extending millions of kilometers.
它的核心直径被认为约1.6公里，其尾巴延伸数百万公里。
The comet is not expected to be nearly as bright as Neowise in 2020, or Hale-Bopp in the mid to late 1990s.
预计这颗彗星不会像2020年的新智彗星那样明亮，也不会像20世纪90年代中后期的海尔-波普彗星那样明亮。
Karen Meech of the University of Hawaii said in an email to the Associated Press that the comet "will be bright by virtue of its close Earth passage ... which allows scientists to do more experiments and the public to be able to see a beautiful comet."
夏威夷大学的卡伦·米奇在发给美联社的一封电子邮件中说，这颗彗星“由于距离地球很近，所以会很亮……这让科学家们可以做更多的实验，让公众能够看到一颗美丽的彗星。”
Scientists are confident in their calculations, putting the comet's last pass through the solar system at 50,000 years ago.
科学家们对他们的计算很有信心，他们认为这颗彗星上一次穿过太阳系是在5万年前。
However, they do not know how close it came to Earth or whether it was even visible to the Neanderthals, said Chodas.
然而，乔达斯说，他们不知道它离地球有多近，也不知道尼安德特人是否能看到它。
When the comet returns, though, is more difficult to estimate.
然而，彗星何时返回就更难估计了。
Every time the comet passes the sun and planets, their gravitational pulls change the comet's path by small amounts.
每次彗星经过太阳和行星时，它们的引力会轻微地改变彗星的轨迹。
However, these small effects lead to major path changes over time.
然而，随着时间的推移，这些微小的影响会导致大的路径变化。
There is another source of measurement difficulty.
还有一个导致测量困难的原因。
Large amounts of dust and gas come off the comet as it heats up near the sun.
当彗星靠近太阳时温度会上升，大量的尘埃和气体从彗星上释放出来。
"We don't really know exactly how much they are pushing this comet around," Chodas explained.
乔达斯解释说：“我们真的不知道它们到底把这颗彗星推了多远。”
The comet — an ancient object produced from the emerging solar system 4.5 billion years ago — came from what is known as the Oort Cloud well beyond Pluto.
这颗彗星是45亿年前从新诞生的太阳系中产生的一颗古老天体，它来自冥王星之外的奥尔特云。
This area is believed to extend more than one-quarter of the way to the next star.
这一区域是太阳与邻星距离的四分之一多。
While comet ZTF began in our solar system, we cannot be sure it will stay there, Chodas said.
乔达斯说，虽然ZTF彗星起源于我们的太阳系，但我们无法确定它是否会留在那里。
If it gets sent out of the solar system, it will never return, he added.
他还说，如果它离开太阳系，它就永远不会回来了。
However, you should not worry if you miss it.
然而，如果你错过了它，你不必担心。
"In the comet business, you just wait for the next one because there are dozens of these," Chodas said.
乔达斯说：“你只需等待下一颗彗星，因为有几十颗这样的彗星。”
"And the next one might be bigger, might be brighter, might be closer."
“下一个可能更大，可能更亮，可能更近。”
I'm John Russell.
约翰·拉塞尔为您播报。
译文为可可英语翻译，未经授权请勿转载！
