The Secret Life of the Sun Page #6

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But that didn't stop

early astronomers from trying.

And just sometimes, maybe at sunrise

or sunset or on a cloudy day,

they'd see something

that made the sun worth looking at -

tiny dark spots.

And for years,

they just assumed that those spots

were planets that were passing

between the Earth and the sun.

And then the telescope was invented,

and Galileo could draw

diagrams like these

and map out

where these dark spots were.

And it became apparent

that they're actually part of

the surface of the sun.

Thanks to those early astronomers,

sunspots are one of

the few bits of evidence we have

about the sun's long-term behaviour.

And new research is revealing

something surprising about them.

The key is how they're created.

Sunspots are caused by the magnetic

fields deep inside the sun,

and we can't see

those magnetic fields directly,

but the sunspots are offering us

some clues as to what's going on.

And we know that the more active the

sun is, the more sunspots there are.

As the sun approaches solar maximum

and the magnetic field lines

beneath its surface become tangled,

the flow of plasma within

is disrupted.

Hot material from the interior

can't rise to the surface.

The result is zones of cooler plasma.

Sunspots.

They're like windows

in the sun's surface,

through which we can study what's

happening inside the sun itself.

The McMath solar telescope in Arizona

is the largest in the world.

17 years ago,

a study of sunspots began here,

led by a group of astronomers,

including Matt Penn.

'They began to look

at the average strength

'of the magnetic fields

in the sunspots.'

So here we have the main mirror...

'Something no-one had tried before.'

So what got you started

on this study?

So we wanted to take

regular observations of the sun

to find out what sunspots were doing

over time.

We know that the number of sunspots

increases and decreases

in the solar cycle.

Actually, that's how the solar cycle

was discovered,

by early observations of sunspots.

During solar minimum, there'd be

zero or five sunspots on the disc.

During maximum, there could be 100.

During that 11-year period,

we wondered what was happening

to the magnetic fields in sunspots.

Was it increasing

along with the number of sunspots?

Was it flat, or was it doing

something else? We just didn't know.

And is it what you'd expect?

Well, no, it turns out

that the data showed us

something completely different.

Matt and colleagues are using

an ingenious way of measuring

the strength of the magnetic field

and sunspots.

A change in the infrared light

coming from them.

So this is a really lovely,

simple method,

because you can point your telescope

at any point on the sun

because you can point your telescope

at any point on the sun

and from the light coming out of it,

this simple thing of watching

how these spectral shapes change,

you can see exactly

how strong the magnetic field is

anywhere on the face of the sun.

Exactly, so we measure the magnetic

field with the spectral line,

and we've done a survey of 3,000

sunspots over the past ten years,

measuring the magnetic field

strength in each sunspot.

And what they've discovered

is surprising.

Instead of rising and falling

in line with the solar cycle,

as expected,

the magnetic strength of sunspots

has been steadily decreasing

year by year.

Right back in 2000,

the magnetic field was quite high,

and it's just gradually

gone down and down and down

over the past ten years,

quite consistently.

So a decreasing trend

means that in the future,

we may not have any sunspots at all.

It's an extraordinary result.

The trend suggests

that, over and above

the familiar 11-year solar cycle,

there are bigger patterns

in the sun's activity.

And in the long-term, we may be

heading for an extended quiet period,

what solar scientists call

a grand minimum.

Intriguingly, we've been here before.

Thanks to those historical records,

we know that around 350 years ago,

sunspots almost vanished

for 70 years.

So it looks as though

the sunspots could be dying away.

If that happens,

what difference does that make to us?

Right, if sunspots do go away

and we enter a new grand minimum,

there are possible effects

on the climate.

Records suggest the temperature

in Europe, for instance,

decreased during

the last grand minimum.

A grand minimum

would be a double-edged sword.

It might mean fewer solar storms,

something in our favour.

But it could also mean

a dramatic change in our weather.

The previous grand minimum

coincided with a period

of brutally harsh winters

in Europe and North America.

The River Thames in London

famously froze solid.

It was known as the Little Ice Age.

So this is a sort of intriguing time,

right?

You can see maybe just the start

of these big changes,

but you can't quite see

why they're happening.

But there are potentially very big

impacts if they do. Exactly.

This data suggests that the sun

is going through a major change,

a global change on the sun.

So in the long-term life of the sun,

we'd love to know what's going on.

If this trend does continue,

it may be evidence of a bigger

cycle in the sun's behaviour

that we've only just begun

to glimpse.

But the sun works

on such vast timescales,

even several hundred years of data

can give us only a tantalising clue.

So we've been watching the sun

for a few centuries,

but we don't know what was happening

when the pyramids were being built,

or when the dinosaurs were alive,

or a billion years ago.

And we don't know

what's going to be happening

a billion years into the future,

so we're just seeing this tiny, tiny

sliver of the lifetime of the sun,

and it's really hard to imagine that

in this enormous timescale.

And that's the big challenge

that lies ahead for solar scientists.

What's emerging is that even

the pattern we thought we knew,

the 11-year solar cycle,

isn't the full story.

There are bigger, longer-term

patterns in the life of our sun,

and they could have profound

influences on our planet and others.

What's incredibly exciting

is just how quickly our knowledge

of the sun is growing.

And thanks to huge technological

and scientific advances,

its surprises are gradually

being uncovered.

And next time you feel the sun

warm your cheeks

or you admire a sunrise,

it's worth remembering

just how complex and wonderful

our local star really is.

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