了解宇宙是如何运行的（2010）

How the Universe Works S08E09

Part 3 Jan. 30, 2022, 2:59 p.m.

继续向右倾斜，但在数十亿年的时间里
tilted right over,
but over billions of years,
月球的引力将地球垂直拉起
the moon's gravity pulled
the earth upright,
只是不是完全垂直
just not completely.
月球并不完全在地球的赤道平面上
The moon is not quite in the
equatorial plane of the earth.
它位于赤道平面上方
It's above the equatorial plane,
它把地轴拉成23又1/2度的倾斜
and it pulls the earth's axis
into a 23 1/2-degree tilt.
斯特里克:如果没有23度的倾斜
Stricker: If we didn't have
the tilt to about 23 degrees,
我们就不会有季节
then we wouldn't have
the seasons,
而这些季节推动了很多作物的生长
and these seasons drive a lot of
the crops and the growth
和全球的生存能力
and the ability to survive
all across the globe.
但是撒哈拉沙漠古老的绿化
Narrator: But the ancient
greening of the sahara
不能用季节的变化来解释
can't be explained
by the changing seasons.
另一个行星的运动肯定在起作用
Another planetary motion
must be in play.
在夜空中找到了一条线索——
A clue is found in the
night sky --
北极星
the north star.
现在，地球的地轴指向天空中的一颗星星
Right now, the earth's axis
is pointed towards a star
这颗星星叫做北极星
in the sky called
the north star -- polaris.
我们实际上是以地球北极
We've actually named it
after the fact
在天空中指向来命名这颗星星的
that the north pole of the earth
points toward it in the sky.
但北极星并非一直都是北极星
Narrator: But polaris hasn't
always been the north star.
五千年前，它是一颗完全不同的恒星
5,000 years ago,
it was a totally different star.
这是右枢，它位于天龙座
It was thuban,
which is in draco,
一个不同的星座
a different constellation.
在未来的某个时候，它将会是织女星
Sometime in the future,
it'll be vega,
天琴座中最亮的一颗星
the brightest star
in the constellation lyra,
所以北极星实际上会改变
so the north star
actually changes
因为北极在天空中的位置改变了
because the north pole's
position in the sky changes.
不断变化的北极星
Narrator: The changing pole star
is evidence
是地球在太空中摇摆的证据
that earth is wobbling
through space.
这个过程叫做进动
It's a process called
precession,
它也会影响陀螺的旋转
something that also affects
spinning tops.
普莱特:如果你拿一个陀螺，让它快速旋转
Plait: If you take a top
and let it spin really rapidly
然后戳它
and poke it,
它的旋转轴会像这样旋转
the axis of rotation
will spin around like this,
这比物体的实际自转速度要慢得多
and it's much slower than
the actual spin of the object.
这就是进动，是这个轴画的圆
That is precession, this circle
that the axis is making.
这也同样发生在地球上
This happens to the earth,
as well.
♪
一个宇宙的戳引起了地球的空间摆动
narrator: A cosmic poke caused
earth's space wobble,
但是什么有能力戳一颗行星呢？
but what has the power
to poke a planet?
♪
再一次，关键是引力
once again, the key is gravity,
这一次是地球与月球和太阳的引力
this time earth's
gravitational interactions
相互作用
with the moon and sun.
这些力戳在旋转的地球上
These forces are that poke
on the spinning earth,
这就是为什么地球的轴在进动中旋转
and that's what makes the
earth's axis spin in precession,
大约需要20000年才能形成一个完整的圆
and it takes about 20,000 years
to make a complete circle once.
随着地球继续绕太阳公转
Narrator: As the earth continues
its journey around the sun,
进动极大地改变了地球的气候
this precession changes the
planet's climate dramatically.
当地球的北极向太阳倾斜时
When the earth's north pole
leans toward the sun,
北半球的夏天阳光更充足……
northern hemisphere
summers are sunnier...
♪
而这给撒哈拉沙漠带来了意想不到的后果
with unexpected consequences
for the sahara.
♪
兰皮诺:事实证明，当撒哈拉
rampino: It turns out
that at times when
得到更多的阳光时
the climate in the sahara
gets more sunshine,
气候就会变暖
that warms the climate up,
风就会从海洋吹进来
and the winds come in
from the ocean.
这被称为季风效应，将水——
It's called the monsoon effect
and brings water --
以雨水的方式带到这个现在是干燥的撒哈拉沙漠
rain into the sahara,
where now it's dry.
♪
奥尔森:这种干湿气候模式
olsen: This pattern of
wet and dry climates
产生了两万年的循环
that produce this
20,000-year cycle
这就是我们在撒哈拉所看到的
is what we see in the sahara,
在季风强烈的时候
where at times
of strong monsoon,
撒哈拉更潮湿，变成了绿色的撒哈拉
the sahara is wetter,
a green sahara.
一万年前
Narrator: 10,000 years ago,
当地球绕着太阳转动时
as the earth wobbled
around the sun,
季风爆发，沙漠变绿
monsoons were unleashed,
turning the desert green.
人类迁移到新近茂盛的撒哈拉沙漠
Humans migrated to the
newly lush sahara
并创造了我们今天看到的洞穴壁画
and created the cave paintings
we see today.
♪
但这并不是人类第一次穿越撒哈拉沙漠
but this wasn't the first time
humans crossed a green sahara.
♪
达特纳尔:干燥的撒哈拉沙漠
dartnell: A dry sahara
would have presented
会给我们的祖先提供一个
an insurmountable barrier
不可逾越的障碍，让他们无法从非洲迁移出去
to our ancestors
for migrating out of africa,
但在撒哈拉沙漠是绿色的一个周期中
but during one of these cycles
when the sahara was green,
它会是一条
it would have been a corridor
我们可以迁移和分散的走廊
that we could have migrated
and dispersed on.
♪
随着地球在宇宙中旅行
narrator: As the earth
traveled the cosmos,
我们星球的进动改变了撒哈拉沙漠
our planet's precession
changed the sahara
和人类的命运，但还有更多的宇宙力量
and the fate of humankind,
but there are more cosmic forces
在影响着我们在宇宙中的旅行
affecting our journey
through the universe.
地球绕太阳的轨道是另一个
The earth's orbit around the sun
is another thing
看起来非常非常坚固的东西
that seems very, very solid.
我们知道它是如何工作的，但宇宙中的一切
We understand how it works,
but everything in the universe
都是一场微妙的引力之舞
is a delicately tuned
dance of gravity,
即使受到微小的影响，事物也会发生变化
and things can change even
from tiny little influences.
当我们的星球在太空中飞驰时
Narrator: As our planet
hurtles through space,
其他世界影响着我们的路径
other worlds influence our path.
一个行星霸王会把地球的气候推向极端吗？
Could a planetary bully push
earth's climate to the extreme?
[冰裂]
[ ice cracking ]
♪
地球带我们在宇宙中展开了一场狂野之旅
narrator: Earth carries us on a
wild journey through the cosmos.
♪
而这次旅行影响的线索
and clues to the effects
of this trip
就藏在我们自己的后院