Name: How Does the Earth Move? Crash Course Geography #5
Uploaded: 2022-06-03T05:48:34.000Z
Duration: 10 min 33 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

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So, I grew up in a house wrapped around a 300 year-old oak tree.

And maybe that's where my fascination with how we adapt to our ever-changing physical

As a kid, I learned to live in constant balance with nature as it was, quite literally, part

It wasn't something to control, but respond to.

In winter, we watched for weak branches that could break under the pressure of heavy snow

In spring and summer, we monitored fellow residents of our Oak tree, like squirrels,

chipmunks and carpenter ants, who wrought havoc on our home as they went about making theirs.

And in autumn, we spent hours raking the leaves that buried our house under a golden layer

Going through my childhood art box shows how intimately the natural world was a part of my life.

Or even better, from a drawing that my sister did, weren't all homes basically trees?!

I grew up with a unique perspective on how impermanent and alive the Earth is, and how

constant change, even on geologic timescales, influences our daily lives.

Everything from windstorms to ocean waves is directly linked with the predictable rhythms

Motion, it turns out, that started back in the early days of the galaxy before the Earth

To start our journey into physical geography, we're going to go back to the beginning of... everything.

I'm Alizé Carrère and this is Crash Course Geography.

Geography is all about appreciating “the big picture” to reveal the geographic patterns

and processes that create Earth's environments and support all living things.

So in the big, big picture, about 13.7 billion years ago, the universe began.

We could talk about the physics of that for a whole episode -- and we have! -- but to

get to the story of the Earth, we need to zoom into the Milky Way galaxy.

In one remote arm of one of 125 billion galaxies, about 4.5 billion years ago, a swirling cloud

of gas and dust, called a solar nebula, collapsed under its own gravity.

It spun faster and faster and flattened into a disk.

Almost all of the nebula's material was sucked into the center, forming the Sun, but

a tiny fraction of a percentage spun out.

And that's what formed the rest of the Solar System -- including the Earth.

We can still see the effects of this dramatic event in how the Earth and the rest of the

planets and asteroids move throughout our solar system.

Our whirling and twirling days aren't behind us.

The Earth spins, or rotates, on an imaginary axis that runs from the North Pole through

the center of the planet to the South Pole.

It takes the Earth just under 24 hours, or one day, to spin once on its axis.

At the equator, the Earth is actually spinning at about 1600 kilometers per hour, which to

my brain at least, basically sounds like “very fast.”

But to really get a feel for what's happening, let's use a reference point: a cheetah, one

A cheetah can put on a burst of speed of up to 120 kilometers per hour to bring down that

They could catch those for sure, but I'm talking the car -- on a freeway!

The rotation of the Earth at the equator is still 13 times faster than the top speeds

At the equator, we're moving the fastest because we have to rotate the entire circumference

of the Earth to get back to where we started.

But if we're anywhere else, we move in a much smaller circle.

So if we're in St. Petersburg at 60 degrees North latitude, our speed would be only about

half that at the equator: 830 kilometers per hour, or about 7 times faster than our cheetah.

And at either pole, it's the speed of a cheetah...napping.

So everyday, while we're brushing our teeth or standing in line for bananas or even sleeping,

we're moving faster than a cheetah ever dreamed possible.

Well, as long as you don't live near the North or South poles.

Everything and person on Earth -- including the atmosphere -- is rotating with us.

Which is why we don't recognize that we're spinning.

We don't have any nearby moving objects we can compare Earth's movement to.

While stuck on the surface, we can get some limited help from the main object in our sky, the Sun.

It appears to move because the Earth is rotating, which changes our view of the Sun over the

If we were floating above the North Pole, Earth would be rotating counterclockwise.

That gives the impression of the Sun rising in the east, moving across the sky as it climbs,

And then if we look at the Earth from a distance, like astronauts on the moon, we'd actually

be able to see the Earth rotating because we wouldn't be rotating with it anymore.

In fact, we'd even be able to see the gradual movement of the circle of illumination, which

is the dividing line that separates the half of Earth that's currently receiving light

and solar energy from the other half that's in darkness.

Though we'd have to watch pretty carefully to notice the Earth doesn't spin perfectly.

The Earth, it turns out, doesn't spin like a perfect top.

Some of the Earth's wobbling is actually predictable.

Like a spinning top slowing down, the Earth's axis wobbles on a 26,000 year cycle known

as precession that changes how the Earth's hemispheres are oriented towards the Sun.

So the North Star, or the star almost directly above the North Pole, cycles through several

Precession is one of the Milankovich cycles named after the mathematician who deduced

Milankovich cycles influence Earth's climate by changing how much solar energy reaches the Earth.

But in 2000, the wobble took an unexpected and relatively “rapid” turn east.

So with the help of the GRACE satellites launched by NASA and the German Aerospace Center to

record data on anomalies in Earth's gravity field, scientists looked for answers in the

They found that melting ice from Antarctica and Greenland are causing sea level rise,

which affects land masses too, pushing and pulling the Earth as it rotates.

But human water use in Eurasia is having an effect too!

Groundwater beneath the surface is being used faster than the hydrosphere can naturally

But as we get closer to 45 degrees north or south latitude, small changes have a big impact.

Coefficients in the equations that best describe the Earth's wobbling depend on latitude,

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