Derhaps the greatest, mind-bending quirk of our universe is the inherent trouble with timekeeping: Seconds tick by ever so slightly faster atop a mountain than they do in the valleys of Earth. For practical purposes, most people don't have to worry about those differences.
也许我们宇宙中最令人困惑的奇异现象就是关于计时的固有难题：地球上，时间在山顶会比在山谷过得略快。从实际用途来看，大多数人无需担心这些差异。
On the lunar surface, a single Earth day would be roughly 56 microseconds shorter than on our home planet-a tiny number that can lead to significant inconsistencies over time. NASA and its international partners are looking to create an entirely new "time scale," or system of measurement that accounts for that fact that seconds tick by faster on the moon.
在月球表面，一个地球日会比在地球上短大约56微秒，虽然这个数字很小，但随着时间的推移会导致显著的不一致。美国国家航空航天局（NASA）及其国际合作伙伴正在寻求创建一个全新的“时间尺度”或测量体系，以应对月球上时间走得更快这一事实。
Such a framework will be crucial for humans visiting our closest celestial neighbor. Astronauts on the moon,for example, are going to leave their habitats to explore the surface and carry out science investigations. They're also going to be communicating with one another or driving their moon buggies while on the lunar surface.i"When they're navigating relative to the moon," said Cheryl Gramling, the lunar position, navigation, and timing and standards lead at NASA's Goddard Space Flight Center in Maryland, "time needs to be relative to the moon."
这样的框架对人类探访宇宙中我们最近的邻居至关重要。例如，月球上的宇航员将离开他们的驻地，去探索月球表面并进行科学调查。他们还需要在月球表面相互通讯或驾驶月球车。“当他们在相对于月球的位置进行导航时，时间也需要以月球的为准。”美国马里兰州戈达德航天飞行中心的月球定位、导航与授时系统标准化项目负责人谢丽尔·格拉姆林说。
A brief history of Earth time
地球时间简史
Simple sundials or stone formations,which track shadows as the sun passes overhead, mark a day's progression just as the shifting phases of the moon can log the passing of a month on Earth.Those natural timekeepers have kept humans on schedule for millennia. But perhaps since mechanical clocks gained traction in the early 14th century, clockmakers have grown ever more persnickety about precision.
简单的日晷或石堆通过追踪太阳在头顶移动所产生的影子来标记一天的进程，正像月亮的盈亏变化可以记录地球上一个月的流逝。这些天然计时器已让人类遵循着时间的轨迹度过了数千年。但可能从14世纪初机械时钟开始普及以来，钟表制造者们在精准度方面就变得越来越挑剔。
Exacting the measurement of seconds also grew more complicated in the early 1900s, thanks to Albert Einstein,the German-born physicist who rocked the scientific community with his theories of special and general relativity.
520世纪初，德国出生的物理学家阿尔伯特·爱因斯坦提出狭义和广义相对论，震撼了整个科学界，对秒的测量也变得更为复杂。
General relativity is complicated,but in broad terms, it's a framework that explains how gravity affects space and time. Imagine that our solar system is a piece of fabric suspended in the air. That fabric is space and time itself, which,under Einstein's theories, are inextri cably linked. And every celestial body within the solar system, from the sun to the planets, is like a heavy ball sitting atop the fabric. The heavier the ball, the deeper the divot it creates, warping space and time. Even the idea of an earthly"second" is a humanmade concept that's tricky to measure. And it was Einstein's theory of general relativity that explained why time passes slightly more slowly at lower elevations because gravity has a stronger effect closer to a massive object(such as our home planet).
广义相对论很复杂，但大体上说，它是一个解释引力如何影响空间和时间的框架。想象一下，我们的太阳系是一块悬空的布，这块布就是空间和时间，根据爱因斯坦的理论，二者密不可分。而太阳系内,从太阳到行星的每个天体都像是放在布上的重球，球越重, 它造成的凹陷就越深，从而使空间和时间发生扭曲。就连地球上“秒”的概念也是人为创造的，难以精确测量。而爱因斯坦的广义相对论解释了为什么在低海拔地区时间走得要稍微慢些一因为离一个大质量物体：（比如我们居住的地球）越近，引力的影响就越大。
Scientists have found a modern solution to all the complications of relativity for timekeeping on Earth: To account for imperceptible differences,they have set up a few hundred atomic clocks at various locations across the globe. Atomic clocks are ultra-precise instruments that use the vibration of atoms to measure the passage of time,and those clocks-in line with Einstein's theoriestick slower the closer to Earth's surface they sit. The readings from atomic clocks around the world can be averaged for a broad but accurate as possible sense of time for planet Earth as a whole, giving us Coordinated Universal Time, or UTC. Still, occasionally "leap seconds" are factored in to keep UTC in line with slight changes in Earth's speed of rotation.
科学家们已找到一个现代方法，可解决在地球上计时所要面对的所有相对论复杂性：为了应对难以察觉的差异，他们在全球各地设置了数百个原子钟。原子钟是超精密仪器，利用原子的振动来测量时间的流逝。这些时钟越接近地面走得就越慢，与爱因斯坦的理论相符。将世界各地原子钟的读数取平均值，就可以获得宏观但尽可能准确的地球整体时间概念，让我们有了协调世界时（UTC)。不过，有时仍会考虑使用“闰秒”，以使世界时与地球自转速度的细微变化保持一致。
Space, time: The continual question
空间与时间：永恒的问题
If time moves differently on the peaks of mountains than the shores of the ocean, you can imagine that things get even more bizarre the farther away from Earth you travel. To add more complication, time also passes slower the faster a person or spacecraft is moving, according to Einstein's theory of special relativity. Astronauts on the International Space Station are lucky, said Dr. Bijunath Patla,a theoretical physicist with the US National Institute of Standards and Technology, in a phone interview. Though the space station orbits about 200 miles(322 kilometers) above Earth's surface,it also travels at high speeds-looping the planet 16 times per day-so the effects of relativity somewhat cancel each other out. For that reason, astronauts on the orbiting laboratory can easily use Earth time to stay on schedule.
如果山顶和海岸的时间不同，那么你可以想象，离地球越远，情况就越奇怪。根据爱因斯坦的狭义相对论，更复杂的是，一个人或航天器运动速度越快，时间过得就越慢。美国国家标准与技术研究院理论物理学家比朱纳特·帕特拉博土在一次电话采访中说，国际空间站上的宇航员是幸运的。虽然空间站在距地表约200英里（322公里）的绕地轨道上，但它也在高速运行——每天绕地球飞行16圈——因此相对论的效应在某种程度上会相互抵消。正因如此，在轨实验室里的宇航员可以轻松地借助地球时间按计划开展工作。
For other missions, it's not so simple. Fortunately, scientists already have decades of experience contending with the complexities. Spacecraft, for example, are equipped with their own clocks called oscillators. "They maintain their own time," Gramling said. "And most of our operations for spacecraft, even spacecraft that are all the way out at Pluto, or the Kuiper Belt, like New Horizons, rely on ground stations that are back on Earth. So everything they're doing has to correlate with UTC.”But those spacecraft also rely on their own kept time. Vehicles exploring deep into the solar system, for example, have to know—-based on their own time scalewhen they are approaching a planet in case the spacecraft needs to use that planetary body for navigational purposes, she added.
对于其他任务来说，情况就没那么简单了。幸运的是，科学家们在应对这些复杂问题上已有几十年的经验。例如，航天器上都配备了名为振荡器的自有时钟。格拉姆林说：“它们有自己的计时。而我们对航天器的大部分操作都要依靠地球上的地面站，甚至包括像‘新视野号’那样远在冥王星或柯伊伯带的航天器。所以它们所做的一切都必须与UTC相关联。”但那些航天器也使用其自身的计时系统。比如，深入太阳系探索的飞行器必须根据自己的时间尺度去确定何时接近某颗行星，以防该航天器需要利用那颗行星进行导航，格拉姆林补充道。
For 50 years, scientists have also been able to observe atomic clocks that are tucked aboard GPS satellites, which orbit Earth about 12,550 miles (20,200 kilometers) away, or about one-nineteenth the distance between our planet and the moon. Studying those clocks has given scientists a great starting point to begin extrapolating further as they set out to establish a new time scale for the moon."We can easily compare GPS clocks to clocks on the ground." said Patla.
50年来，科学家们还能够观察搭载在GPS卫星上的原子钟，这些围绕地球飞行的卫星距离地球约12,550英里（20.200公里），大约是地球与月球距离的1/19。研究这些原子钟为科学家们提供了一个极好的起点，使他们能在着手为月球建立新时间尺度的同时进行进一步推断。帕特拉说：“我们可以轻松地将GPS时钟与地面上的时钟进行比较。”
Patla recently co-authored a paper detailing a framework for lunar time.Clocks on the moon's equator would tick 56.02 microseconds faster per day than clocks at the Earth's equator, according to the paper.
帕特拉最近与人合著了一篇论文，详细阐述了月球时间框架。该论文指出，月球赤道上的时钟每天会比地球赤道上的时钟快56.02微秒。
A whole different mindset
完全不同的思维方式
12 Accurate clockwork is one matter. But how future astronauts living and working on the lunar surface will experience time is a different question entirely. On Earth, our sense of one day is governed by the fàct that the planet completes one rotation every 24 hours,giving most locations a consistent cycle of daylight and darkened nights. On the moon, however, the equator receives roughly 14 days of sunlight followed by 14 days of darkness. "NASA is talking about landing astronauts in the very interesting south polar region of the moon,where you have permanently lit and permanently shadowed areas. So, that's a whole other set of confusion. It'll be challenging for those astronauts. It's so diferent than Earth, and it's just a whole different mindset." said Dr. Bruce Betts,chief scientist at The Planetary Society, a nonprofit space interest group.
精确计时是一回事，但末来在月球表面生活和工作的宇航员将如何体验时间则完全是另一个问题。我们在地球上对一天的概念是由地球每24小时自转一周决定的，这使得大多数地区都有一个稳定的昼夜循环。然而，月球赤道地区会有大约14天的白昼，随后是14天的黑夜。非营利性太空兴趣组织行星协会的首席科学家布鲁斯·贝茨博士说：“NASA正在商议将宇航员送到月球颇为有趣的南极区域，那里有永久光照区和永久阴影区。所以，这完全是另一种复杂情况。对宇航员来说，这将是很具挑战性的。它与地球差异太大，需要一种完全不同的思维方式。”
The beauty of creating a time scale from scratch is that scientists can take everything they have learned about timekeeping on Earth and apply it to a new system on the moon. And if scientists can get it right on the moon, they can get it right later down the road if NASA fulfills its goal of sending astronauts deeper into the solar system. "We are very much looking at executing this on the moon, learning what we can learn," Gramling said, "so that we are prepared to do the same thing on Mars or other future bodies."
从头开始创建一个时间尺度的美妙之处在于，科学家们可以将其在地球学到的所有计时知识应用到月球的新系统中。倘若科学家们能在月球上做到这一点，那么如果NASA实现将宇航员送人太阳系更深处的目标，他们也能在未来的任务中做到这一点。“我们非常关注在月球上执行该任务，学习能学到的东西，这样我们就能做好准备，在火星或未来其他天体上做同样的事情。”格拉姆林说。
