发表于 2025年10月18日
This week, Earth gets a front-row seat to one of the solar system’s oldest relics. On October 21, Comet C/2025 A6 (Lemmon) will pass closest to Earth—its first and only appearance for more than a thousand years.
“Comets are very common, but Comet Lemmon is definitely the best comet to view from Earth this year,” says Rhonda Stroud, the director of the Center for Meteorite Studies at Arizona State University in Tempe, Arizona.
Where did this comet come from—and how can you spot it in the night sky? Here’s what to know before it passes.
WHERE DID THE COMET COME FROM?
Space isn’t completely empty. Within our solar neighborhood, it’s sprinkled with ice and dust particles that can be found between planets, stars, and even galaxies. Comets and asteroids are evidence of the ice and dust found in our solar system—the debris left over from the solar system’s formation from a huge, dense cloud of gas and dust about 4.6 billion years ago.
After the sun ignited, the leftover gas and dust began clumping together. Far from the heat, in the cold outer reaches, comets formed. Those icy outskirts later became the Kuiper Belt and the even more distant Oort Cloud—vast reservoirs filled with frozen comets.
“Comets are fantastic to study because they are treasure troves of the original building blocks of our solar system,” says Stroud. “The frozen state of comets means that much of the dust and ice is essentially unchanged over billions of years.”
WHY ARE SO MANY COMETS CALLED LEMMON?
When Comet Lemmon first appeared on January 3, it wasn’t much to look at—just a faint dot against the night sky. Carson Fuls, director of the Catalina Sky Survey and the observer on duty that night, says that’s typical. “Sometimes we won't see them until they ‘turn on,’” says Fuls, or when they get close enough to the sun for their ices to turn to gas and form the characteristic tail of the comet.
Despite the name, this is far from the first Comet Lemmon. Fuls says it is one of around 70 “Comet Lemmons,” and that comets are often named after the observatory that detected them, or the person who discovered it, if they recognize it right away as a comet. For Fuls, this Comet Lemmon wasn’t “turned on” yet, so it more resembled an asteroid than a comet with a tail.
“I usually see a few [comets] each night when running one of our survey telescopes, but they are still a treat. It never gets old seeing so deep into such large sections of the night sky,” says Fuls.
WHY DOES COMET LEMMON GLOW GREEN?
While dozens of comets pass through the inner solar system each year, Comet Lemmon’s brightness, distinctive green glow, and proximity to Earth make it the most striking comet of 2025. The emerald hue is due to the presence of diatomic carbon (C2), a molecule that gets broken down by solar radiation and emits green light.
The light blue tail is actually made up of two tails: one made of ice and dust from the comet itself, and one made of ions, or energetic particles that are excited when the comet “turns on” as it gets closer to the sun’s radiation.
Common comet ingredients include carbon monoxide, carbon dioxide, and water ice, but the ratios between the molecules vary, says Stroud. “Every comet that we have imaged up close with a spacecraft looks different from the others.”
Comets are also unusually dynamic. Their shapes and brightness can change within hours as sunlight and heat reshape their frozen surfaces and blow material off of the main part of the comet.
“You can sometimes see disruption events as chunks of the comet are flung off. These look like ripples in the tail that you can watch slowly evolve,” says Fuls. “It’s rare to see something so dynamic out in space.”
For many researchers studying comets, the next scientific holy grail would be a sample return mission to bring back a frozen chunk of a comet and study its ancient ice and dust, right as it appeared in space.
“The more I learn about [comets], the more I feel connected to the history of the universe,” says Stroud. “Following the comet dust is like following the breadcrumbs to solve the mystery of how our solar system, and ultimately you and I, came to be.”
HOW TO SEE COMET LEMMON
Comet Lemmon will be closest to Earth on October 21, coinciding with a new moon, a dark-sky advantage that makes faint celestial objects easier to see. Look for a soft green glow near the constellations Scorpius or Libra, low on the western horizon shortly after sunset. The comet should remain visible from mid-October through early November, fading gradually as it moves away from Earth.
“While it is fun to look with just your eyes, I recommend binoculars and taking pictures with a good phone or digital camera. You’ll be able to see more of the coma,” says Stroud, the glowing cloud of gas and dust that surrounds a comet’s icy core.
Adding to the spectacle, October 21 also marks the peak of the Orionid meteor shower, offering a rare double feature in the night sky. For the best viewing experience, astronomers suggest using stargazing apps or NASA’s Sky Events calendar to check exact rise and set times for your location.
This week, Earth gets a front-row seat to one of the solar system’s oldest relics. On October 21, Comet C/2025 A6 (Lemmon) will pass closest to Earth—its first and only appearance for more than a thousand years.
本周，地球将迎来一个近距离观测太阳系最古老遗迹之一的机会。10月21日，C/2025 A6（莱蒙）彗星将飞掠地球，届时它将与地球距离最近——这也是未来一千多年里它首次且唯一一次出现在我们眼前。
“Comets are very common, but Comet Lemmon is definitely the best comet to view from Earth this year,” says Rhonda Stroud, the director of the Center for Meteorite Studies at Arizona State University in Tempe, Arizona.
亚利桑那州坦佩市亚利桑那州立大学陨石研究中心主任朗达·斯特劳德（Rhonda Stroud）表示：“彗星很常见，但莱蒙彗星（Comet Lemmon）绝对是今年从地球上观测的最佳彗星。”
Where did this comet come from—and how can you spot it in the night sky? Here’s what to know before it passes.
这颗彗星从何而来——你又如何在夜空中发现它呢？在它飞过之前，你需要了解以下信息。
WHERE DID THE COMET COME FROM?
彗星从何而来？
Space isn’t completely empty. Within our solar neighborhood, it’s sprinkled with ice and dust particles that can be found between planets, stars, and even galaxies. Comets and asteroids are evidence of the ice and dust found in our solar system—the debris left over from the solar system’s formation from a huge, dense cloud of gas and dust about 4.6 billion years ago.
宇宙并非完全真空。在我们的太阳系附近，散布着冰和尘埃颗粒，它们存在于行星、恒星乃至星系之间。彗星和小行星就是我们太阳系中这些冰和尘埃存在的证据——它们是大约46亿年前太阳系由一大片致密的气体和尘埃云形成时留下的残骸。
After the sun ignited, the leftover gas and dust began clumping together. Far from the heat, in the cold outer reaches, comets formed. Those icy outskirts later became the Kuiper Belt and the even more distant Oort Cloud—vast reservoirs filled with frozen comets.
在太阳形成之后，残余的气体和尘埃开始聚集成团。在远离热量、寒冷的外围区域，彗星得以形成。这些冰冷的边缘区域后来形成了柯伊伯带，以及更遥远的奥尔特云——它们是充满冰冻彗星的巨大储藏库。
“Comets are fantastic to study because they are treasure troves of the original building blocks of our solar system,” says Stroud. “The frozen state of comets means that much of the dust and ice is essentially unchanged over billions of years.”
施特劳德说：“彗星非常值得研究，因为它们是我们太阳系原始组成物质的宝库。”她补充道，“彗星的冰冻状态意味着其中的大部分尘埃和冰块在数十亿年间基本保持不变。”
WHY ARE SO MANY COMETS CALLED LEMMON?
为什么这么多彗星都叫“莱蒙”？
When Comet Lemmon first appeared on January 3, it wasn’t much to look at—just a faint dot against the night sky. Carson Fuls, director of the Catalina Sky Survey and the observer on duty that night, says that’s typical. “Sometimes we won't see them until they ‘turn on,’” says Fuls, or when they get close enough to the sun for their ices to turn to gas and form the characteristic tail of the comet.
1月3日莱蒙彗星首次出现时，它并不显眼，只是夜空中的一个微弱光点。卡特琳娜巡天计划负责人兼当晚值班观测员卡森·富尔斯表示，这种情况很常见。富尔斯说：“有时我们直到它们‘点亮’才看到它们，也就是当它们足够靠近太阳时，彗星的冰会升华成气体，从而形成其标志性的彗尾。”
Despite the name, this is far from the first Comet Lemmon. Fuls says it is one of around 70 “Comet Lemmons,” and that comets are often named after the observatory that detected them, or the person who discovered it, if they recognize it right away as a comet. For Fuls, this Comet Lemmon wasn’t “turned on” yet, so it more resembled an asteroid than a comet with a tail.
尽管叫这个名字，但这颗远不是第一颗“莱蒙彗星”。富尔斯（Fuls）说，这大约是70颗“莱蒙彗星”之一，彗星通常以发现它们的天文台或第一时间将其识别为彗星的发现者命名。对富尔斯来说，这颗“莱蒙彗星”当时还没有“活跃”（turned on），所以它看起来更像小行星而不是拖着彗尾的彗星。
“I usually see a few [comets] each night when running one of our survey telescopes, but they are still a treat. It never gets old seeing so deep into such large sections of the night sky,” says Fuls.
福尔斯说：“我通常每晚在操作我们的巡天望远镜时都会看到几颗[彗星]，但它们仍然是令人兴奋的景象。能深入观察如此广袤的夜空，我总是百看不厌。”
WHY DOES COMET LEMMON GLOW GREEN?
莱蒙彗星为何会发出绿光？
While dozens of comets pass through the inner solar system each year, Comet Lemmon’s brightness, distinctive green glow, and proximity to Earth make it the most striking comet of 2025. The emerald hue is due to the presence of diatomic carbon (C2), a molecule that gets broken down by solar radiation and emits green light.
尽管每年有数十颗彗星穿过内太阳系，但莱蒙彗星的亮度、独特的绿色光芒以及它与地球的距离，使其成为2025年最引人注目的彗星。这种翠绿色调是由于双原子碳（C2）的存在——这种分子会被太阳辐射分解并发出绿光。
The light blue tail is actually made up of two tails: one made of ice and dust from the comet itself, and one made of ions, or energetic particles that are excited when the comet “turns on” as it gets closer to the sun’s radiation.
这条淡蓝色的彗尾实际上由两条彗尾组成：一条由彗星本身的冰和尘埃构成，另一条由离子，即当彗星靠近太阳辐射时“活跃起来”而被激发的高能粒子构成。
Common comet ingredients include carbon monoxide, carbon dioxide, and water ice, but the ratios between the molecules vary, says Stroud. “Every comet that we have imaged up close with a spacecraft looks different from the others.”
斯特劳德表示，彗星的常见成分包括一氧化碳、二氧化碳和水冰，但这些分子之间的比例各不相同。“我们用探测器近距离拍摄到的每一颗彗星，看起来都与其他彗星不同。”
Comets are also unusually dynamic. Their shapes and brightness can change within hours as sunlight and heat reshape their frozen surfaces and blow material off of the main part of the comet.
彗星也表现出异常的动态性。它们的形状和亮度可以在数小时内发生变化，这是因为阳光和热量会重塑它们冰冻的表面，并将物质从彗星主体上吹离。
“You can sometimes see disruption events as chunks of the comet are flung off. These look like ripples in the tail that you can watch slowly evolve,” says Fuls. “It’s rare to see something so dynamic out in space.”
福尔斯说：“有时你会看到瓦解事件，彗星的碎片被抛洒出来。这些看起来就像彗星尾巴上的涟漪，你可以观察它们缓慢演变。在太空中看到如此动态的现象实属罕见。”
For many researchers studying comets, the next scientific holy grail would be a sample return mission to bring back a frozen chunk of a comet and study its ancient ice and dust, right as it appeared in space.
对于许多研究彗星的科学家来说，下一个科学上的“圣杯”（即最重要、最难实现的目标）将是一项样本返回任务，目的是带回一小块冰冻的彗星，并研究其在太空中形成时保持原始状态的古老冰和尘埃。
“The more I learn about [comets], the more I feel connected to the history of the universe,” says Stroud. “Following the comet dust is like following the breadcrumbs to solve the mystery of how our solar system, and ultimately you and I, came to be.”
斯特劳德说：“我对彗星了解得越多，我就越能感受到自己与宇宙历史的联结。追溯彗星尘埃，就像循着面包屑，去揭开我们的太阳系，以及最终你我，是如何形成的奥秘。”
HOW TO SEE COMET LEMMON
如何观测莱蒙彗星
Comet Lemmon will be closest to Earth on October 21, coinciding with a new moon, a dark-sky advantage that makes faint celestial objects easier to see. Look for a soft green glow near the constellations Scorpius or Libra, low on the western horizon shortly after sunset. The comet should remain visible from mid-October through early November, fading gradually as it moves away from Earth.
莱蒙彗星将于10月21日最接近地球，届时恰逢新月，这一黑暗天空的优势将使微弱的天体更容易被看到。在日落后不久，你可以在西方地平线较低的位置，寻找天蝎座（Scorpius）或天秤座（Libra）附近柔和的绿色光芒。这颗彗星应该会从10月中旬一直到11月初保持可见，并随着它逐渐远离地球而慢慢变暗。
“While it is fun to look with just your eyes, I recommend binoculars and taking pictures with a good phone or digital camera. You’ll be able to see more of the coma,” says Stroud, the glowing cloud of gas and dust that surrounds a comet’s icy core.
斯特劳德说：“虽然用肉眼观测很有趣，但我建议使用双筒望远镜，并用好的手机或数码相机拍照。这样你就能看到更多彗发——那团环绕彗星冰核的发光气体和尘埃云。”
Adding to the spectacle, October 21 also marks the peak of the Orionid meteor shower, offering a rare double feature in the night sky. For the best viewing experience, astronomers suggest using stargazing apps or NASA’s Sky Events calendar to check exact rise and set times for your location.
为这一壮观景象增添色彩的是，10月21日也是猎户座流星雨达到顶峰的日子，这在夜空中提供了一场难得的“双重盛宴”。为了获得最佳观赏体验，天文学家建议使用观星应用或查阅美国国家航空航天局（NASA）的“天空事件日历”，以查询你所在地的准确升起和落下时间。