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为什么“一天”不一定是24小时 – 译学馆
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为什么“一天”不一定是24小时

Why Some Days Aren’t 24 Hours

《分钟物理》
In the distant future,
在遥远的未来
aliens who live on asteroids near the center of the galaxy
生活在靠近银河系中心的小行星的外星人
get in touch and want to come visit you.
与你取得联系并且想来拜访你
And so you tell them,
于是你对他们说
“Of course, I’m free any day this week.”
“没问题 这个礼拜我每天都有空”
But they don’t know what that means.
但是他们不懂你在说什么
They live in an asteroid belt
他们生活在一个小行星带上
and have a totally different kind of calendar,
那里有着截然不同的历法
and to them, the concept of a “ day ” is very… alien.
对他们来说 “天”这个概念是非常陌生的
So you tell them
于是你告诉他们
that a day is how long it takes for the Earth to complete a full rotation about its axis.
一天是地球自转一周所需要的时间
And as they input that into their computer simulation,
但当他们把地球自转输入电脑模拟时
you notice a fatal flaw in your explanation:
会注意到你的解释有一个致命的漏洞
as the earth rotates relative to the distant aliens,
对于离我们很远的外星人而言
it moves a little bit around the sun
地球自转的同时 也围绕太阳缓缓移动
and by the time it makes its way to the other side of the sun
等到地球转到太阳的另一边
our daytime and nighttime
太阳在正头顶的时候
have somehow switched with the sun directly overhead
我们的白天和夜晚就会以某种方式切换
when one day changes to the next
时间就切换到了第二天
rather than in the middle of the day!
而非在一天正中间的时间点切换
This is not what we mean when we talk about calendar days.
这和我们谈论的历法日不同
What you’ve actually described to the aliens is called a Stellar day
而你向外星人描述的实际是恒星日
and it’s measured with respect to a distant,
它是根据一个遥远的
more or less stationary reference point far off in space, like aliens,
相对太空而言静止的参考点来测量的 比如外星人
but our concept of a day has more to do with the sun,
但我们对一天的概念更多是与太阳有关
not the galactic center.
而不是和银河系中心有关
So you try again.
所以你试着再解释一次
This time you tell them that when Earthlings look up at the sky
这次你告诉他们 当地球人仰望天空的时候
for each turn of the earth
地球每转动一周
there’s a time when the sun is highest.
太阳都会在某个时间处于最高点
And a day is the time it takes
而一天就是
for the Sun to get back to the highest point.
太阳重新回到最高点所花的时间
And so the Asteroid-ians tap away on their instruments
接着小行星人敲击他们的仪器
calibrating them to your insightful specifications
根据你的解释来校正他们的观念
until you notice their day counter isn’t staying in sync with your clock!
直到你发现他们的计时器和你的时钟是不一致的
It’s starting the new day earlier,
他们的计时器新的一天来得更早
and earlier and earlier each… day.
而且每一天都比前一天更早
And then later, and later, and later.
然后后来的每一天又比前一天更晚些
This isn’t a bug in their programming –
这并不是他们程序上的漏洞
it’s a feature… of the Earth’s orbit.
这是地球轨道的特征
What you actually described to them is called a Solar day,
你向他们描述的实际是太阳日
and it’s not the same thing
这和表记录的一天
as a day kept by a clock.
不是同一个概念
Solar days use the sun as a reference point for when “noon” is,
太阳日是以太阳作为“正午”的参考点
but the length of time between when the sun is highest isn’t constant –
但是太阳位于最高点的时间间隔并不是恒定的
it changes up or down by a minute over the course of the year.
一年里 这个时间间隔在一分钟内来回变化
This discrepancy is due to the complications of the earth’s orbit being elliptical and
这种差异是由于地球的轨道是椭圆形的
the earth’s spin axis being tilted.
还有自转轴的倾斜共同造成的
If we used solar days in everyday life,
如果我们在日常生活中使用太阳日
we’d either need to have calendars and clocks that changed the number of
我们要么需要 能根据一年里的时间
minutes and seconds in a day depending on the time of year
来改变一天分钟数和秒数的日历和时钟
or we’d need to have clocks that changed the length of a second
要么就需要能根据一年里的时间
(or changed the number of seconds in an hour) depending on the time of year.
来改变一秒钟的长度(或是改变一小时内秒数)的时钟
And sundials kind of automatically do this!
而日晷几乎能自动完成这些!
But they have other… drawbacks.
不过日晷也有些缺点
Anyway, changing the length of a second or the number
总之 改变一秒钟的长度
of seconds in an hour isn’t particularly
或者改变一小时的秒数
appealing for regular – or interplanetary – use.
并不是很适应常规或行星间的使用
And so you tell the asteroidaliens that
所以你告诉那些外星人
a day is – more or less – an invented time period
一天 或多或少 是一个虚构的时间段
that is 24 hours long,
就是24小时
where each hour is 33 trillion oscillations of a special kind photon emitted by a cesium atom.
一小时即铯原子跃迁时辐射的特殊光子 振动33万亿次的时间
And if they want to know
如果他们想知道
why a day is just defined to be a fixed time period and
为什么一天被定义为一个固定的时间段
how that time period actually relates to the rotation of the earth,
那个时间段实际上又是怎样与地球自转产生联系的
you can send them over to
你可以给他们发送
our interactive video over on MinuteLabs.
我们在MinuteLabs上发布的交互视频
It will guide anyone and everyone through
它会指引每个人去了解
the details of solar,stellar and standard 24 hour day
太阳日 恒星日和标准24小时日的详情
how they’re related;
以及它们之间的关联
and how the orbit of the earth affects them.
以及地球运行轨道对它们的影响
Not only that, but it also lets you play around with different orbits to see how it changes
不止这些 你还可以通过调整不同的运行轨道来观察
the length of those days!
一天的长度是如何被改变的
The link is in the video description,
这个链接在视频简介中
or you can just go to minutelabs.io
你也可以进入minutelabs.io
and look for the “What is a Day?” lab,
查看 “什么是一天?”实验室
and you’ll be fully prepared
这样你就能做好充分准备
to coordinate a visit with aliens
来迎接外星人的访问了
no matter what day that may be.
不管那将是哪一天

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“天”的切换是以什么为标准的?一天是24小时吗?《分钟物理》给你答案。

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视频来源

https://www.youtube.com/watch?v=Vxz6nNqpDCk

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