Do We Really Need the Moon? Page #4

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Well, for one thing,

if it keeps going, we'll lose a great natural wonder.

One of the benefits of astronomy is you get to stay up very late.

And if you don't go to bed at all, you can catch the Moon setting

while the sun rises.

What an amazing sight.

There the rising sun, and opposite the setting Moon.

They both look exactly the same size,

but that's an optical illusion.

Let's take these two balls.

The golf ball is much smaller than the tennis ball

and you can tell that when they are side by side.

But if I move the golf ball towards you,

you can see it's getting bigger and at this point,

they look to be the same size.

Now, it's exactly the same with the Sun and the Moon.

The Moon is actually 400 times smaller than the Sun.

But it's also 400 times closer,

and so they appear to be the same size.

And that's what gives us the most mesmerising sight,

a total eclipse.

Because the Moon's disc is the same size as the Sun's,

they line up perfectly,

with just a halo of solar gases spilling out around the rim.

I always thought there must be some astronomical reason for this,

something in the physics to make it so.

But no, it's just a cosmic coincidence.

It happens because right now,

the Moon is just the right distance from Earth.

But in the future, as the Moon keeps drifting away,

its disc will be too small to cover the sun

and we'll lose the magic of the total eclipse.

And then what?

As the Moon moves away from us, how will life change here on Earth?

New York City.

The sun went down an hour ago,

and the Moon is rising.

It may look familiar enough

but this Moon is smaller than normal in the night sky.

That's because it's further away.

Not much, an extra 10%,

just 24,000 miles.

But that makes a big difference.

The spin of the Earth has slowed down

and days are getting longer.

The sun will not rise here for another 20 hours.

The entire Western hemisphere has to endure a very long night.

While on the other side of the world,

there's an extra-long day.

But things get worse.

If the Moon were to really move by that 10%,

then the very stability of the planet would be threatened.

You see, the Moon,

which controls our tides and the spin of the earth

serves another critical function.

It keeps us stable.

To understand why, meet hoop wizard Jack Ryan.

As Jack runs rings around me, look how he keeps that ball spinning.

- Jack, what's the secret?

- Speed.

You got to keep it fast, it's got to be going fast.

- Would you like to try?

- I'd love to. What do I do?

Just stay still. Let me see your finger.

There you go.

So the ball is just like planet Earth.

The faster it spins, the more stable it is.

- But what happens if it slows down?

- Let's see.

That's lots of wobble and, ooh, I lose control.

So that's just like the Earth -

when it's spinning very fast, it's very stable, but as it slows down,

it loses stability and starts to wobble like crazy.

Ever since the great collision that formed the Moon,

the Earth has been tilted,

spinning at 23 degrees.

This tilt has played a crucial role in shaping our climate.

If the Earth wasn't tilted, if it were upright,

then the sun's light would shine evenly over the surface throughout the year.

Always overhead at the equator,

and barely reaching the North and South poles.

The temperature would be constant throughout the year,

there'd be no summer or winter.

No variation at all.

But because of that 23 degrees tilt,

the light hitting the Earth's surface varies throughout the year.

It's this variety of light that's so important.

It means that throughout the year,

conditions on the planet are always changing.

In our summer, the light favours the northern hemisphere,

giving us warmer temperatures and longer days.

But six months later,

as the Earth travels to the other side of the sun,

the light now favours the southern hemisphere,

leaving us in the cold and dark with shorter days and longer nights.

In other words, we have seasons.

The life cycle of so many animals and plants

is driven by the beat of the seasons.

A burst of life in spring.

Balmy days of summer.

Migration in autumn.

A fight for survival in winter.

But the Earth only stays at this 23 degree tilt

because of the Moon's stabilising effect.

As the Moon keeps drifting away, the angle of the tilt will change.

And over time, the Earth will wobble.

And what will happen then?

It's possible we'll go the same way as Mars.

Mars - our planetary neighbour.

Today, it spins at an angle of 25 degrees,

very similar to Earth.

But it used to spin at a very different angle,

anything up 60 degrees.

You see, unlike Earth,

Mars has no large moon to keep it stable

so it wobbles chaotically.

It could almost tip over onto its side.

We may suffer the same fate if our Moon moved just that 10% further away.

It makes me wonder what would our world be like?

Probably very wet.

If the Earth tipped over and spun on its side,

then for three months of every year the poles would be exposed

to direct unrelenting sunshine.

Pretty quickly, the ice caps would melt.

And a huge amount of fresh water would flood the world's oceans.

Sea levels would rise by more than 60 metres.

Every coastal city in the world would be gone.

And inland areas that survived would be transformed.

Las Vegas is dark

and very cold.

It's minus 20.

Because the sun is pointing at Antarctica,

Vegas is in the grip of a freezing winter.

But in the spring, the snow melts,

the sun rises higher and higher in the sky.

Over the summer, the sun never sets.

In autumn, it's high in the sky.

And then it drops below the horizon again.

And the freezing winter returns.

Could we survive?

Probably, with enough air conditioning and artificial light.

But what of other life forms?

Dr Lynn Rothschild is an astro-biologist working for NASA.

Death Valley is the hottest place in North America.

And it turns out that as the Moon recedes from the Earth,

as it goes away,

there are going to be times that the Earth

tips over further on its side,

and what's going to happen then is that there are going to be

parts of the Earth that become excruciatingly hot in the summer,

much hotter than Death Valley is today.

And in the winter these same places are going to be bitterly cold,

much colder than your freezer.

There are organisms that can survive at reasonably low temperatures,

think of penguins and whales, and so on.

But high temperature is extremely tricky.

When you get up at about 70 degrees centigrade which is hot,

but it's nowhere near the boiling temperature of water, chlorophyll breaks down

so all the greenery you see around you would be gone.

So that means no photosynthesis?

Absolutely, so no photosynthesis, and that's what drives life on Earth today, photosynthesis.

Now, as you go up even beyond that,

your nucleic acids end up breaking and unravelling,

and this is your very genetic material.

So, clearly, you cannot survive without these.

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