1小时读懂天文（速成课堂天文篇-）

Besides the Sun, the Moon is the most obvious object in the sky.，我来为大家讲解一下关于1小时读懂天文?跟着小编一起来看一看吧!

1小时读懂天文

Besides the Sun, the Moon is the most obvious object in the sky.

除了太阳，天空中最明显的物体就是月亮。

Bright, silvery, with tantalizing features on its face, it's been the target of imagination, poetry, science, and even the occasional rocket.

它明亮耀眼、银光闪烁，惹人遐思，是人们想象、歌颂、研究的对象。

If you pay even the most cursory attention to it, you'll see that it changes every day; sometimes it's up in the day, sometimes at night, and its shape is always changing.

如果你稍加留意，就会发现月亮每天都在变化，有时白天出现，有时晚上出现，形状也不断变化。

What causes this behavior?

是什么导致了这种现象呢？

The Moon is basically a giant ball of rock 3500 kilometers across hanging in space.

月球基本上就是一个悬挂在太空中、直径3500公里的巨大的岩石球。

Its surface is actually pretty dark, with about the same reflectivity as a chalkboard or asphalt.

它的表面其实非常暗淡，只有大约相当于黑板或者沥青的反射率。

However, it looks bright to us because it's sitting in full sunlight; the Sun illuminates it, and it reflects that light down to us here on Earth.

然而，对我们来说，它看起来很明亮，因为它沐浴在充足的太阳光中；太阳照亮月球，而月球将光线反射到地球上。

And because it's a sphere, and orbiting the Earth, the way we see it lit by the Sun changes with time.

又因为月亮呈球状，且绕着地球转，所以我们所看见的月球被照亮的方式会随时间变化。

That's what causes its phases: geometry.

这就是月相形成的原因：几何学。

The important thing to remember through all this is, because the Moon is a ball and in space, half of it is always illuminated by the Sun!

始终要记住的是，由于月亮是太空中的一个球体，它的一半永远被太阳照亮。

This is true for the Earth, too, and every spherical object in space; half faces the Sun, half faces away.

地球也一样，任何太空中的球状物都如此，它们一半面朝太阳，一半背朝太阳。

We call the part facing the Sun the daylight or bright side, and the half facing away the night or dark side.

我们称面对太阳的部分为日照面或亮面，称背对太阳的一面夜晚面或暗面。

The phase of the Moon refers to what shape the Moon appears to us; how much of it we see illuminated from the Earth.

月相指在我们看来月亮是什么形状，即从地球上能看到的被照亮的部分有多少。

The key to all this is this line, dividing the lit day side from the unlit night side.

理解月相的关键就是月球明暗面的分界线。

We call that line the terminator.

我们称之为晨昏线。

If you're facing the moon, with the sun behind you, you're seeing the half of the moon that is fully illuminated by sunlight and it looks full.

如果你正对月球，同时太阳在你身后，你就会看见完整的月球被照亮的一面，即满月。

If you're off to the side you see half of the lit side and half of the dark side and we say the moon is half full.

如果你侧对月球，就会看见一半亮面和一半暗面，即半满月。

If the sun is on the other side of the moon, you're look at the unlit half, and it looks dark.

如果太阳在月球背面，你就会看到月球没被照亮的一面。

Now, mind you, I haven't moved anything except our point of view here, so at all times the Moon is always half lit, and half dark.

现在我要提醒你，我没有移动任何东西，仅仅改变了我们观察月亮的角度。

Remember that.

要记住这一点。

The phase of the Moon we see depends on from what direction the sunlight's hitting it, and the angle we see that from Earth.

我们看到的月相取决于阳光照射的方向，以及我们从地球上看月亮的角度。

The Moon orbits the Earth roughly once per month.

月球大约每月绕地球一周。

In fact, that's where the word "month" comes from; "month" and "Moon" are cognates, words that have similar etymological histories, and in most languages, including English, the two words are very similar.

事实上，这就是英文中“月份”（month）这个词的由来；“month”和“Moon”是同源词，它们有着相似的词源历史，在包括英语在内的大多数语言中，这两个词都非常相似。

The length of time we call the month is derived from the length of time it takes the Moon to go through all its phases — 29.5 days.

我们称为一个月的时间长度来源于月亮经历所有月相所需的时间——29.5天。

So. To describe the phases, let's start at the beginning: New Moon.

那么，为了描述月相，让我们从头开始：朔月。

New Moon happens when the Sun, Moon, and Earth are all more or less in a line.

朔月在太阳、月亮和地球基本在一条直线上的时候出现。

The Moon's orbit is actually tipped a bit to the Earth's, so sometimes new Moon happens when the Moon is "below" the Sun, or "above" it.

月球的轨道实际上略朝地球偏斜，所以有时朔月会发生在月球处于太阳下方或上方的时候。

But at some point in its orbit, at some point in the month, it appears to be as close to the Sun as it can.

但是在每月的某个时刻，在月球轨道上总有某个点会距太阳最近。

What does this look like from Earth?

此时月亮是什么样子的呢？

The Moon is between the Earth and the Sun, so from our perspective we only see the dark half, the unilluminated half, of the Moon.

月亮正处于地球和太阳之间，所以从我们的角度上只能看见月亮的暗面，即不被照亮的一面。

The other side, the far side, of the Moon is lit, but we can't see it.

而另外一侧，距我们较远的一侧，月亮正被照亮，但我们看不见它。

It makes sense then to call this the beginning of the Moon's cycle, hence the term "New Moon".

人们把这个月相周期的起始成为“朔月”是名副其实的。

Now think about this for a sec: because the Moon is near the Sun in the sky, it travels across the sky with the Sun.

现在想一下：当月球在天空中离太阳很近的时候，它会随着太阳一起划过天空。

It's up during the day!

这意味着它将在白天出现！

You can only see it from the part of the Earth that's lit, which is when it's daytime.

你只能在地球被照亮的一面，也就是白天看到月亮。

It's a very common misconception that the Moon is only up at night, but it's up during the day literally just as often.

月亮只在夜晚出现是一个常见的误解，其实它在白天和在晚上出现一样常见。

At New Moon, the Moon stays near the Sun, so it rises at sunrise, and sets at sunset.

朔月时，月亮靠近太阳，所以它在日出时升起，日落时落下。

This makes it extremely difficult to see; it is, after all, sitting next to the brightest object in the sky, and only a little bit of it is lit from our perspective.

这导致月亮很难被看到，毕竟它正呆在天空中最亮的物体边上，并且从地球上只能看到非常小的被照亮的部分。

But not for long.

不用多久。

Because the Moon is orbiting the Earth, after a couple of days it's moved a bit to the east.

由于月球绕地球旋转，几天后它向东移动了一点。

Now we're seeing it along a slight angle, and we can see a little bit of the illuminated half of the Moon on its side toward the Sun.

现在我们沿一个小小的角度看向月亮，就能看见它面朝太阳被照亮的一部分。

The terminator, the day/night line, appears curved around the Moon, so what we see is a thin illuminated crescent Moon.

晨昏线，即昼夜线，在月球周围呈曲线状，所以我们看到的是一弯窄窄的新月。

At this point, the crescent is still very thin, with the horns of the crescent pointing away from the Sun.

此时，月亮很窄，月牙凸起的角指向远离太阳的地方。

Note that the Moon is still pretty close to the Sun in the sky, just a bit to the east, rising maybe an hour or two after sunrise.

注意月亮此时在天空中仍然十分靠近太阳，只偏东一点点，它在日出前后一小时左右升起。

But this means it's up all day, and then sets after the Sun does.

也就是说它整个白天都在空中，然后在日落后落下。

This is the best time to see the crescent Moon, when the Sun has already set and the sky starts to get dark.

此时是最适合观察新月的时间，即太阳下山，天空开始变暗的时候。

The Moon will be low over the western horizon, and it will set soon after the Sun does.

此时月亮会低悬在西面的地平线之上，并在太阳下山后很快也会落下。

Let's wait a couple of days.

让我们稍等几天。

OK, now the Moon has moved a bit more in its orbit around the Earth, and is farther from the Sun in the sky.

好了，现在月球又沿着轨道移动了一点，离太阳更远了。

We see a little more of the illuminated part, and the crescent is wider.

我们能看到更多被照亮的部分，新月更宽了。

Since it's getting thicker, we say this is a "waxing crescent" Moon; waxing means growing or getting bigger.

由于它变宽了，我们就称之为“娥眉月”；“waxing”在英文中有生长、变大的意思。

It's also well away from the Sun now, so it's easier to spot, even during the day before sunset.

现在它离太阳也更远，所以更容易被看到，即使是在日落之前的白昼也能看到。

Seven or so days after new Moon, we get to our first milestone: the Moon is now one-quarter of the way around its orbit.

在朔月后七天左右，我们就到达了第一个里程碑：月球现在已经绕其轨道运行了四分之一的路程。

It's 90° away from the Sun in the sky, which means we're looking straight down on the terminator, the Moon's day/night line.

它与天空中的太阳形成90度夹角，这意味着我们正直视着晨昏线，即月亮的昼夜线。

It cuts right down the middle of the visible face of the Moon, so it's half lit, with the sunward side of the Moon visible and the other side dark.

它正好把月球可见的一面分成两半，所以月亮半亮半暗，朝向太阳的一半可见，另一半黑暗。

Confusingly, this phase is properly named "first quarter" because the Moon is one quarter of the way through its cycle, one quarter of the way through its orbit around the Earth, even though it looks half full.

容易混淆的是，英文中这个月相成为“四分之一月”，这个名称是正确的，因为月球正经过了四分之一的周期，运行了绕地球轨道的四分之一，虽然它看起来是半满的。

So it's not really the half-full moon — astronomers prefer "first quarter," so if you want to sound all astronomery, then you should call it that.

但它实际上不是半满月——天文学家更喜欢称之为“四分之一”月，所以如果你想要听起来像个天文学家，在英文中就这么叫它。（中文叫上弦月）

But time marches on.

时间是会流逝的。

The Moon continues on its gravitational dance with Earth, swinging around its orbit.

月球继续与地球引力共舞，绕其轨道旋转。

Now more than half full, we say its shape is "gibbous", which means swollen or convex.

现在月亮已经超过了半满，我们就称这个形状为“凸月”，英文中“gibbous”的意思是肿起或凸起的意思。

Since it's getting wider, this is actually the waxing gibbous phase of the Moon.

由于月亮正变得越来越宽，实际上这是“盈凸”月相。

It rises in the late afternoon, and is up most of the night.

它在傍晚时升起，几乎整个夜晚都在空中。

Our next big step comes two weeks after new Moon, when it's moved halfway through its orbit.

下一个重要步骤发生在朔月两周之后，此时月亮已经走完了一半的轨道。

It is now opposite the Sun in the sky, 180° around.

它现在与太阳在天空中的位置相反，是180度。

The Earth is between the Moon and Sun, so we're looking at the fully-illuminated half of the Moon.

地球在它们中间，所以我们能看见月球完整的被照亮的一面。

This is the full Moon.

这就是满月。

Because it's opposite the Sun, it rises at sunset and sets and sunrise; it's up all night shining down on the Earth.

因为它是对着太阳的，它在日落时升起，在日落时落下，在日出时升起；整夜都照耀着大地。

But again, wait a couple of days and things change.

再过几天，事情继续变化。

When the Moon is full, it's 180° around the sky from the Sun, so as it continues to move around the Earth in a circle the distance between it and the Sun is now starting to decrease, even as it continues on in the same direction.

满月时，月亮与太阳呈180°，所以当月亮继续绕着地球转动的时候，它与太阳之间的距离就开始缩小，即使它是在继续朝着同一个方向运行。

As before, it keeps rising and setting later, but now it rises after sunset, and sets after sunrise.

和以前一样，月亮起落的时间继续推迟，现在它在日落之后升起，在日出之后落下。

If you get up early in the morning as the Sun is just rising in the east, you'll see the nearly-but-not-quite full Moon setting in the west.

如果你早上起得很早，在太阳刚从东方升起之时起床，你就会看到几乎是满月的月亮正在西方落下。

Not only that, but we're about to go through all the phases again, but in reverse order.

不仅如此，我们马上就要以相反的顺序再次经历各个月相。

A few days after full Moon, the lit side is shrinking.

满月的几天之后，月亮开始缩窄。

It's in the waning, or shrinking, gibbous phase.

处于“亏突”的状态。

Then, three weeks or so after new Moon, and a week after full, the Moon is once again half lit, the terminator splitting the Moon's face in two even halves.

朔月三周，即满月一周后，月亮再次半满，晨昏线把月亮分成两半。

This is the "third quarter" Moon, because the Moon is three quarters of the way through its cycle.

在英文中称为“四分之三”月（中文下弦月），因为月亮走过了其四分之三的周期。

It's a lot like the first quarter, but the side that was lit is now dark, and vice versa.

虽然看起来像上弦月，但实际上明暗面对调了。

It's 270° around the sky from the Sun.

它与太阳呈270度角。

It rises at midnight and sets at noon.

在午夜时升起，正午落下。

A few days later and the Moon is a crescent again, getting thinner.

几天后，月亮继续变窄。

It's now a "waning crescent."

成为残月。

It rises just a couple of hours before sunrise, and sets a couple of hours before sunset.

它在日出前几小时升起，在日落前几小时落下。

Then, finally, we're back where we started.

最后，我们又回到起始点。

One month after new Moon, the Moon has traveled 360° around the sky, and is once again as close to the Sun as it can get.

朔月一个月后，月亮走了360度，再一次达到距太阳最近的点。

It's new Moon, and the cycle starts up again as it has for time immemorial.

又成了朔月，继续这个始于远古的循环。

An interesting thing happens if you move your perspective from the Earth to the Moon.

如果你把视角从地球移到月球，会发生一件有趣的事情。

The phases of the Moon we see from Earth depend on the angle of the Moon and Sun in the sky.

我们从地球上看到的月相取决于月球和太阳在天空中形成的角度。

But on the Moon, the angles are exactly 180° reversed; at new Moon, when the Moon is between the Earth and Sun, the Earth is opposite the Sun as seen from the Moon.

但在月球上，这个角度正好反了180°；朔月时，月亮在地球和太阳之间时，而从月球上看，地球和太阳位置相反。

It's full Earth!

这是“满地”！

All the other phases are opposite too, so when we see a full Moon, a Moon-dweller would see a new Earth, and so on.

其他月相也都相反，当我们在地球上看到满月时，在月球上会看见“满地”，以此类推。

Have you ever looked at the thin crescent Moon and seen the ghostly face of the rest of the unlit side?

你是否曾经觉得能够在娥眉月时隐约看见月亮没被照亮的一面？

That's because it's not really unlit: the nearly full Earth is reflecting sunlight on the Moon, lighting up the otherwise dark part.

这是因为它并非完全找不到光线：“满地”正阳光反射向月球，照亮了月球本该黑暗的一面。

The Earth is bigger and more reflective than the Moon, so it's actually 50 times brighter than a full Moon!

地球比月球更大，反射能力更强，所以它的亮度实际上是满月的50倍！

This glow is called Earthshine, a term I quite like.

这种光叫做地球反照（Earthshine），我很喜欢这个词。

Even more poetically, it's been called "the old Moon in the new Moon's arms", referring to the unlit part surrounded by the crescent new Moon's horns.

更有诗意的说法是“新月臂弯中的旧月”，指的是被包围在新月弯中的黑暗部分。

That's lovely, isn't it?

很可爱，不是吗？

The Moon is one of the most beautiful and most gratifying objects in the sky to observe.

月亮是天空中最美丽、最可爱的物体之一。

It's different every day!

它每天都不一样！

Yet it's also the same, because we see, more or less, the same half of it, the same face all the time.

但它却又是一样的，因为基本上我们看到的始终是月球相同的一面。

It's big and bright, and the features on its surface discernible by eye (and even better with binoculars or a small telescope).

它又大又亮，表面的特征用肉眼就能分辨出来（当然用双筒望远镜或小型望远镜就更好了）。

As the phases change, inexorably, day after day, the angle of sunlight hitting the surface changes, bringing new things into our view.

随着月相的变化，日复一日，阳光照射地面的角度也在变化，把新的事物带入我们的视野。

The motions become comforting, even familiar.

这种变化让人感到熟悉、舒适。

It's a reminder that the Universe may seem strange and complicated and forbidding at first, but over time, as you get outside and experience it, it becomes your neighborhood.

它提醒我们，宇宙起初可能看起来陌生、复杂、令人生畏，但随着时间的推移，当你走到外面去体验它时，它就变成了你的邻居。

Welcome home.

欢迎回家。

Today you learned why the Moon has phases: It's a sphere, and it orbits the Earth, so the angle at which we see its lit side changes.

今天你学习了为什么月球有不同的相位：因为它是一个球体，它围绕着地球运行，所以我们看向它被阳光照亮的一面的角度会变化。

It goes from new, to waxing crescent, to half full, waxing gibbous, full, waning gibbous, half full, waning crescent, and then the cycle starts all over again.

依次经过朔月、娥眉月、上弦月、盈凸月、满月、亏凸月、下弦月、残月，循环往复。

This also affects when it rises and sets, and what we see on the surface.

这也影响月亮何时升起落下，以及我们能在它的表面看到什么。

Crash Course is produced in association with PBS Digital Studios.

Crash Course 是与 PBS 数字工作室联合制作的。

This episode was written by me, Phil Plait.

我是菲尔·普莱特，这一集是由我创作的。

The script was edited by Blake de Pastino, and our consultant is Dr. Michelle Thaller.

脚本由 Blake de Pastino 编辑，我们的顾问是 Michelle Thaller 博士。

It was co-directed by Nicholas Jenkins and Michael Aranda, and the graphics team is Thought Café.

本片由尼古拉斯·詹金斯(Nicholas Jenkins)和迈克尔·阿兰达(Michael Aranda)联合执导，视频画面团队是 Thought Cafe。

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