Do We Really Need the Moon? Page #3

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It's called the Transylvania Effect.

One police force in the south of England

was so convinced, they put extra officers on the beat at a full Moon,

just in case.

But is it true? Does the Moon really change our behaviour?

Well, sadly, I don't think so.

For every study claiming an effect, there are many more dismissing it.

The theory probably stems from the fact that when the Moon is full, the sky is much, much brighter.

In the past, before electric lights, people were more likely to go out on a bright night,

so there was more chance for trouble.

These days, alcohol is surely a far more important factor

than the light of a full Moon.

But even if the Transylvania Effect is a bit of a myth,

the Moon is still very powerful.

There are many animals which react instinctively to the light of the full Moon.

They become more active, more vocal,

more fertile.

Most remarkable of all are these tropical corals.

Every year they synchronise their reproductive cycle,

so on one night they all spawn together.

And for these corals, it's triggered by the full Moon.

The Sargasso Sea, off the coast of Bermuda.

Marine biologist Dr Anne Cohen is studying how the Moon affects the growth of corals.

She's looking for a species known as Diploria strigosa,

the brain coral.

Every 29 days, on a full Moon,

brain corals grow a new layer of skeleton on top of the old.

This growth spurt is dictated by the monthly orbit of the Moon.

It's like clockwork.

And the skeletal layers can be used as a lunar calendar,...

..a record of time passing.

So, this is the coral that we pulled out of the water today.

And if we look under the microscope,

you can see very fine ridges

and we know that these are formed on the lunar cycle, these are monthly bands.

- So it's a bit like the rings of a tree, you can use that to date it.

- That's right.

And we can count about 65 monthly bands in this coral,

which makes it just over five years old.

That's pretty amazing!

'But some corals are even more revealing.

'They allow us to peer into the distant past

'and find out something extraordinary about the power of the Moon.

'This is a fossil coral from the Devonian era.

'It's 400 million years old

'but still beautifully preserved.

'As well as monthly growth bands, there are annual bands

'and even daily bands, a quarter of a millimetre apart.'

So this coral grew about a quarter of a millimetre every day 400 million years ago.

And if we took the time to count up all these daily growth bands,

within the year we'd find...

not 365 days

but in fact in this coral there are 400 bands every year.

- 400 bands?

- Per year.

- So that means that there were an extra 35 days every year?

- That's right.

That's quite mind-boggling.

'If there were really 400 days in the year back then, how long was each day?'

If you do the sums, and take the total number of hours in a year

and divide by 400 days, then you come to the conclusion

that in the Devonian period, when this fossil was alive,

a day actually lasted 21 hours and 55 minutes.

Now I must admit I find that really weird.

The fact that in the past, a day wasn't 24 hours.

The length of a day is simply the time it takes for the Earth to spin once

and go from one sunrise to the next.

If, in the past, days were shorter,

then the Earth must have been spinning faster.

In fact, back in time, back billions of years,

the planet was spinning so fast

that each day lasted just five hours.

But why should the spin of the Earth have changed over time?

Because of the Moon.

When the Moon formed, it was so close to the Earth,

and pulling so hard that it acted as a brake on our planet.

The gravitational pull of the Moon was slowing the Earth's spin

and it's still doing so.

As the Earth spins,

the effect of friction between the ocean bulge and ocean floor

causes the Earth's spin to slow down.

It means days have been getting longer.

What was once was five hours now lasts 24.

We humans have been around for such a short time,

about 200,000 years,

that we've only ever known 24 hour days.

Our body clocks are completely geared for that length of day.

And yet, we only have 24-hour days because of the Moon.

It's amazing to think that the very rhythms of our planet

have been set by this ball of rock out in space.

But what about the Moon itself?

How has it been affected by the spin of the Earth?

One of the first things you learn in physics is that for every action

there is an equal and opposite reaction.

As the Earth has been slowing down all these years,

something else has been accelerating,

and that's the Moon.

And to compensate for its acceleration,

something's been happening to its orbit at the same time.

Imagine the centre of this roundabout is the Earth, and I'm the Moon in orbit.

As we speed up, I get slung outwards,

and I feel as if my body wants to move into a wider orbit.

And that, more or less,

is what's been happening to the Moon.

To balance out its acceleration, it's been spiralling outwards,

into a wider and wider orbit.

But is it still spiralling away?

Or has it stopped?

There's one way to find out.

Apache Point Observatory in New Mexico...

..one of America's largest telescopes.

It's also one of the last outposts of the Apollo programme.

Besides having a lot of fun on the Moon,

the Apollo astronauts were running a series of scientific experiments.

And on three of the missions they left behind retro-reflector units,

packed with small mirrors.

This one is from Apollo 15.

And ever since, astronomers have been firing lasers at them

to keep track of exactly how far away the Moon is.

So once we're all centred up on Apollo 15,

I can open the shutter and we're ready to shine the laser.

Dr Russet McMillan carries out the laser ranging at Apache Point.

So you're now sending pulses of laser-light out towards the Moon.

That's right, they're going to travel to the Moon,

get reflected, come back, and get detected by our detector.

So how much of the light do we actually get back?

Well, we're sending out about 100 quadrillion photons with each pulse.

If we're lucky, for each pulse we might get back one photon.

One photon back?

One photon out of 100 quadrillion going out.

A photon is a tiny particle of light and 100 quadrillion is...

a phenomenally large number!

But by capturing just a few photons,

it's possible to measure

the distance between the Earth and the Moon

down to the last millimetre.

As of right now, the distance to the Moon

is 393,499km,

precisely.

Astronomers have been using lasers to measure the Moon's distance for nearly 40 years now.

And what they're finding amongst all those photons is a very clear pattern.

The Moon, which has been drifting away from us for billions of years,

is still drifting,

at a speed of 3.78 cm a year.

In human terms,

that's about the same speed that our fingernails grow!

Does it matter that the Moon is drifting away from us?

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