The Transit of Venus Horizon

MUSIC: Little Green Bag by George Baker Selection

# Yeah...

# Lookin' back... #

Just after 11 o'clock tonight,

a rare event is going to take place in our solar system

and it won't happen again in our lifetime or that of our children or even our grandchildren.

In fact, it won't happen again for over a century.

In just a few hours' time,

Venus will begin its journey across the face of our sun,

giving us the opportunity to watch its transit for the very last time.

This is going to be a truly beautiful spectacle,

but it is far more than just that.

It's helping us answer some of the most profound questions we can ask

about life in our own solar system.

And it's helping astronomers explore the realms of much more distant stars in the search for life

-on planets hundreds of light years away.

-You need to keep watching

because tonight is your very last chance to witness the transit of Venus.

This is the Observatory Science Centre, for decades the home of British astronomy.

And in just two hours it will all begin.

Across the globe right now, telescopes are being aligned and focused on Venus

so that we can better understand the secrets of our universe.

Transits represent some of our greatest scientific achievements

and to me they stand for our insatiable desire to constantly push the boundaries of our knowledge

and to explore the unknown.

So tonight it feels like I'm part of a very special moment in history

and it's a moment that you can be part of, too.

'As stargazers across the world are getting ready,

'we'll be showing you why this event is so important.'

You're sure that's Venus?

'From the first transits that are the basis of all modern astronomy

'to the one tonight that's helping us search for alien life.

'And if you want a piece of the action for yourself, we'll be showing you how.'

The reason the transit of Venus is so rare is that you need an unlikely set of events

to all come together. So this is Venus and the Earth in orbit around the sun.

Now Venus travels faster than the Earth.

And its orbit is shorter.

For a transit to happen, it has to overtake us, but that only happens once every 1.6 years.

Not only that, but Venus's orbit is tilted compared to the Earth's

at an angle

of 3.4 degrees.

And that means that Venus's and Earth's orbits will only ever cross at two points.

But because of the relative speeds of Earth's and Venus's orbits

and because of their position relative to the sun,

only two transits, separated by eight years, will happen every 100 years or more

and one of them is happening tonight.

'All astronomy today is built on one particular transit that happened over two centuries ago

'and observing it led to one of the most epic voyages in history.'

On August 26th, 1768,

Captain James Cook, then a young lieutenant, embarked on one of the greatest ever voyages of discovery.

It was a journey that was fraught with danger. The men on board knew

that half of them probably wouldn't make it home alive.

But it was all for one magnificent goal,

to reach Tahiti in time to observe the transit of Venus.

For me, Cook's voyage was like a modern space mission,

a voyage of discovery, a testing ground for the latest technologies,

but above all a test of human endurance. Just like astronauts voyaging into space.

'And in 1768, they believe the transit was a risk worth taking

'because it held the key to a great mystery.

'It promised to reveal nothing less than the size of the solar system.'

As a scientist today, I feel humbled by the lengths people went to in those days to discover new things.

I can't imagine putting myself through that ordeal.

But finding the size of the solar system was the great mystery of the time,

like understanding dark matter or detecting the Higgs-Boson is today.

Observing the transit of Venus was the key to unravelling it.

Without leaving the planet, how could you measure distances out in space?

It had baffled the greatest minds for thousands of years.

Astronomers at the time knew the relative distances of the planets from the sun,

but they didn't know what this distance was in miles.

It was like having a map without a scale.

It was my all-time favourite hero, Edmond Halley, who realised that Venus held the key.

He worked out that if you were in the right place at the right time during the transit,

you could work out the distance between the sun and the Earth

and he did it by using the most beautifully simple solution,

a phenomenon you can observe by holding up one thumb and closing one eye.

The principle is called parallax.

It's the shift you see when you hold up your thumb and look at it first through one eye,

and then through the other.

You can measure the shift in position of your thumb, with the distance between your eyes

and actually work out how far away your thumb is from you.

In a stroke of genius, Halley saw that this simple technique can understand the solar system's size.

He worked out that the problem could be solved

by timing the transit from two very distant points on Earth.

Effectively, it's like drawing the largest triangles ever in space.

To do this, you need widely separated observers on Earth, for example in Canada and Tahiti.

From those two different locations, they see Venus transiting the sun along two different tracks.

And they can work out those tracks very precisely if they time the transits.

That information, along with the distance between your two observers,

allows you to build up the triangles that you need to work out the distance between the Earth and sun.

'And this is why Cook made the 12,000-mile voyage to Tahiti.

'And he wasn't alone.

'Observers were sent to the four corners of the known world in the name of science.

'And after eight months battling stormy seas,

'desertion and even suicide,

'Cook finally reached his destination, just in time to observe the transit.'

When the time came, Cook and the other two observers set up their stations.

They would have had a tent to keep them out of the heat of the sun and, of course, their telescopes

with an all-important filter to block the glaring light of the sun and view the transit directly.

'After the transit passed, Cook and his fellow astronomers compared notes.

'But they found something they weren't expecting.

'There was a difference between their timings.'

What Cook noticed was something called the Black Drop Effect.

I have a copy here of Cook's drawings and you can see

the edge of the sun and then the disc of Venus.

And, literally, a black drop appears between the two.

This mean that getting those crucial timings, the contact times when Venus is at the edge of the sun,

became incredibly difficult.

'But it was a long journey home.

'After the transit, Cook opened his sealed orders.

'They told him to set off in search of unknown lands,

'ones we now know as Australia and New Zealand.

'So it was another two years before they eventually returned with their precious data.'

Finally, back in London, it was down to the mathematicians to crunch the numbers.

They collected data from expedition sites at over 40 locations around the globe

and they came up with a number.

They came up with 93 million, 726 thousand

and 900 miles as the distance between the sun and the Earth.

Now today we know, using modern radar equipment,

that the distance between sun and Earth is just under 93 million miles,

which means, incredibly, in the 1700s they were accurate to within 1%.

'It was a real triumph for science and one that marked the birth of modern astronomy as we know it.'

I find it simply amazing that in 1769 they could work out

the size of the solar system.

And this number, the astronomical unit, couldn't be more important today.

It's the foundation of modern astronomy and without it, my job simply wouldn't exist.

And just to think, they did all this using only the sun and Venus.

It still blows my mind.

In the early hours of tomorrow morning, you, like Captain Cook,

will be able to view the transit.

All around the world, scientists will also be observing and studying it,

but this time they'll be looking for answers to new mysteries.

This is a truly global event

and your view depends on where in the world you're going to be.

Not everyone is going to see the same bit of the transit.

The first contact between Venus and the sun will occur at precisely 23:03:47 our time.

So obviously the first places to see that will be those in daylight,

so we're talking North America, East Asia and most of Australia and New Zealand.

And then for the next six and a half hours, Venus will journey across the sun.

Until, eventually, as the sun rises in the UK

at precisely 05:37:20,

if the skies are clear enough we should be able to spot the third contact

as Venus touches the inner edge of the sun's disc before leaving it for the last time this century.

For hundreds of years, Venus was shrouded in mystery.

Because it's a comparable size to Earth and a similar distance from the sun,

many thought that Venus was just like our own planet.

But there was no real way to know because it lay hidden beneath a thick layer of cloud.

'When they say, "Take me to your leader," and they take them to a creature like this,

'you know they're on planet Venus.'

Because we couldn't see its surface, we could only really hazard a guess at the planet's true identity

and Venus has certainly fired our imagination over the years.

# I'm your Venus, I'm your fire... #

From poptastic tunes to great works of art,

it's even seen highly unscientific attempts at matchmaking.

'The most talked about woman in the world knows what she wants on Venus, too.'

But as for the true Venus, it took us quite some time before we really got to know her.

'Eventually, the Soviets sent a probe to have a look.

'After 16 failed attempts,

'one eventually managed to land on Venus's surface.

'But these first pictures revealed something no one was expecting.'

It soon became clear that our planetary neighbour had a very different temperament to ours

and was nothing like the calm, tropical world we'd imagined.

Venus was, in fact, a hostile, raging inferno,

our polar opposite, our evil twin.

Something had happened to Venus to change its fate,

making it very different to Earth.

And it's a mystery that has led scientists to search for answers here on our own planet.

'If you want to understand Venus, you need to go somewhere a bit like it.

'Somewhere like this.

'Kilauea Iki crater on the big island of Hawaii.'

This may seem pretty nasty, but this is mild compared with Venus

because, for a start, I couldn't be standing on the surface there.

The temperature is 460 degrees Celsius.

That's hot enough to melt lead and certainly too hot for me.

But even if I survived the temperature, the weight of the atmosphere would be crushing me

because the atmospheric pressure on Venus is 92 times that on Earth.

And that is like being squashed by a kilometre of ocean.

'But what I really want to know

'is what happened to Venus to turn it into such a hostile place.

'How did Venus and Earth turn out so differently?

'I spend my life studying the forces that shape our planet

'and I know that the answer to this question lies deep in the heart of these two worlds.

'And that's what scientists are studying here on Hawaii.'

So why, apart from the amazing weather, work in Hawaii?

There are many volcanoes just like Hawaii on Venus.

I've been studying those

for almost 20 years now and Hawaii is a great place to come and see

the volcanoes we can't see directly on the surface of Venus.

I mean, the thing that I really like about volcanoes is that they link

the interior, which is the part that I study most, to the surface, which we can see on other planets.

It feels like we're... I don't want to say like we're on a different planet,

-but that's what I want to say!

-I'm sure it looks a lot like this on Venus.

I think we've reached the end of the road here!

-Wow! Look at that.

-Yeah, geology in action, huh?

-How long has this been here?

-This is less than 10 years old. 2003.

-It just swept over the road. You used to be able to drive all the way across...

-But not any more.

'Sue has been piecing together a picture of what's happening on the surface of Venus

'in an attempt to understand what's going on inside it.'

No humans have ever visited Venus and it's such a long way away,

-how do we know there are volcanoes there?

-Well, in the '90s,

there was a mission that mapped the surface of the planet using radar

so we have these radar images that show us there are these huge volcanoes. This is Maat Mons.

It's about 9km high.

Hawaii, if we measured from the ocean floor, is similarly about 11km high.

-So we're sitting on top of Earth's version of that.

-We're about here!

'The surface of Venus is littered with volcanoes, but the key to understanding its fate

'is not how many there are, but where they're located.

'On Earth, volcanoes sit along the edges of tectonic plates,

'the vast slabs of rock that drift across the surface of our planet.

'But on Venus things are very different.'

-So this is a map of the volcanoes on Venus.

-Well, you can see the little volcanoes poking out,

almost evenly distributed around the planet. On Venus they're everywhere.

Some of them are on these big hot spot areas, some out on the plains.

There are hundreds and hundreds evenly distributed around the planet.

So because there's no pattern of lines, we think Venus doesn't have plate tectonics?

There are big tectonic features, but no plates.

And it's this lack of tectonic plates on Venus that makes Earth and Venus so different.

On Earth, the moving plates are driven by currents of molten rock beneath the surface

making our world a dynamic and changing place.

But Venus has no plates and no dynamic core

and this one difference can mean life or death for a planet.

And it's most obvious with one vital substance.

Water makes our planet what it is - a place teeming with life in all its diversity.

But because of the different way Venus works on the inside,

water is one thing it couldn't keep.

Venus used to be a much more comfortable place to live

because billions of years ago it had liquid oceans.

But it's 30% closer to the sun than we are and that made a crucial difference.

Being that little bit warmer meant that a little bit more water evaporated from the ocean

and that went into the atmosphere as water vapour.

On its own, this wouldn't necessarily have spelt disaster for Venus,

but this is where the two planets took different paths.

The dynamic nature of the Earth's core helps generate a vital magnetic field.

It's this field that shields us from the devastating solar wind

that would otherwise strip our planet of its water.

And this is what happened to Venus.

With no magnetic field to protect it, its water was simply carried off into space.

What I find amazing is that these two planets that had such similar beginnings, Earth and Venus,

have ended up so differently.

Earth has become this beautiful, diverse, living planet

and Venus has become this horrible place, the evil twin.

The surface of Venus is such an extreme environment

that it's impossible to imagine any life forms surviving on it,

but we also know that Venus wasn't always like this.

It once had a much more temperate climate and it had oceans.

So just like Earth it had all the vital ingredients for life

and when life takes hold, it tends to hold on pretty tightly.

So if life did once exist on Venus, is there a remote chance that it's still there today,

hidden somewhere we just haven't thought to look?

'This frozen, icy cave couldn't be more different to fiery, volcanic Venus.'

Wow.

'But hidden in this ice are clues that are challenging our most fundamental assumptions

'about our evil twin.'

The main reason I became a biologist

is because I am constantly amazed by the beautiful, almost unbelievable complexity of life.

And how it manages to find a foothold in the most improbable,

challenging environments.

And it's by studying these hidden oases at the outermost edges of our living world

that we can understand more about how life persists,

both on this planet but also throughout the universe.

And it's by studying extreme environments like this

that scientists like Birgit Sattler are rewriting the story of where life can be found,

even on places like Venus.

Birgit, what are we looking for down here, 30 metres below the surface?

It's dark, it's cold, just frozen, but if you melt this ice up

you will see millions of bacteria just dwelling in this environment.

You can even shine them up. If we do a digital evaluation,

we can actually detect the photosynthetic active pigments.

It's pitch dark normally without the lights and there is still photosynthesis possible.

The microbes thriving here show how life can survive in extreme conditions.

'But to understand Venus we have to hunt for life in an even more distant part of our planet.

'And to find it, we have to go up there.

'In one of these.'

That's as secure as it gets.

Oh, sweet Jesus! Butterflies!

-It's quite speedy.

-Mm-hm.

And windy!

I was told it was a cable car. It's more like a crate,

-supported by metal bars.

-Yeah.

-Has this ever had an MOT?

-What is an MOT?

Ooh. The angle's changing. Is this the 45 angle...? Oh!

Ooh! I didn't like that.

Wow. That's... That was amazing!

'We've come to the top of one of Austria's highest peaks to look for life.

'We're not looking on the ground, but high up in the clouds.'

Some nice clouds surrounding us.

Yeah, even if we don't see here obvious clouds, there are lots of microbes, viruses, algae spores,

fungi floating around. So anything that is floating in the atmosphere we want to catch.

'We've known for a while that microbes exist in the Earth's clouds

'but we thought they were just blown up there. We didn't think clouds could permanently sustain life.'

We attach it to here.

'But we're here to prove otherwise.'

This lovely cloud right there is perfect.

-All right?

-Oh!

So this machine is going to be collecting microbes for a couple of hours now. It's straightforward.

But the key thing here is to be able to prove that the microbes can actively reproduce

and survive up there without the need to get back down to Earth.

And if we can find evidence that life is replicating in these clouds,

it doesn't only tell us something about life here on Earth,

it may also have implications for Venus.

Birgit, Venus is a super-hot, choked greenhouse planet.

We've sent probes there, they've burnt to a crisp.

We concluded there could not be life on that planet.

What does your research here have to do with Venus?

You can actually find one layer in the atmosphere where it's actually habitable

with warm temperatures, but not too hot. We have moisture.

So if you're able to prove that life can reproduce and live happily in the clouds up there,

we can dare to think that it might be possible in this particular cloud layer of Venus? Is it that simple?

It's not that simple, but why not? We have to go step by step.

If we see life is possible here, why shouldn't it be possible in a warmer environment?

Life in Venus's clouds might seem inconceivable.

As well as being very hot, they are also very acidic.

But evidence here on Earth has shown us that life can adapt to highly toxic conditions,

so if Birgit can prove life can live in Earth's clouds,

maybe we were wrong to write Venus off so quickly.

In the lab, the cloud samples are offered DNA which carries a radioactive marker.

If the DNA is taken up, it's proof replication is taking place.

Well, I'm looking here at a sample from the cloud layer which we brought to the lab

and we fixed the sample to get a snapshot of the condition of the cells,

and this is very surprising, but I can see one dividing cell.

-OK, where am I looking?

-If you go to the right side,

so approximately to five o'clock on this slide, you can see it -

-two tiny cells being very tightly together.

-My gosh! Yeah, yeah, yeah.

-Right?

-Oh, yeah.

-Two tiny cells.

-It's tiny.

-Very tightly together.

-Yeah, it's really tiny.

-That is cell replication?

-That's replication, yes.

-That's incredible.

-Yeah.

What about the radioactive basis, the new DNA strands? Have you got any results for that?

This is the outcome of the reaction 24 hours later.

What just looks like dry numbers is actually the proof that the radioactivity is inside the cells,

so it must have been taken up actively.

Absolute proof that replication is going on in the micro-organisms that we sampled from that cloud?

-Right.

-That's huge, Birgit.

-That's the proof, yeah.

So when you first saw this data being crunched up by your computer, how did you feel?

I was just sitting in front of the machine, praying, "Please spit i out, please spit out higher numbers.

-And it did and it was so exciting. I just ran over and said, "I got it!

-To your colleagues?

-Yeah.

It's a wonderful thought that the clouds we thought were hiding Venus's true identity

may be the one place where life exists.

We already know that life on Earth can survive in hot, acidic conditions.

And now we know it can also survive in our clouds.

It's just incredible to think that life has managed to carve a niche out for itself

and thrive up there in the clouds and that we've only just found out about it.

But for me what's most fascinating is what this means for Venus.

We had completely written off the possibility that it could harbour life,

but all this latest evidence makes for a pretty compelling case.

Right now, Venus is hurtling through space at over 78,000 miles per hour,

nearing the perfect position for its transit with our sun.

And it's already incredible how much we've learnt about our solar system from this one planet,

but this year, scientists are hoping that the transit will do even more.

As well as hunting for life in our own planetary neighbourhood,

they will also be turning their attention to the realm of much more distant stars...

..using the transit to hunt for alien life

and possibly even intelligent life.

But what hampers this search is the sheer vastness of space.

To understand the problem,

we need to get a sense of scale,

so there's our sun, the Earth and Venus,

and as we now know thanks to the transit,

the distance between us and the sun is 93 million miles.

Now, that might seem like a lot,

but the distance to the outermost regions of our solar system

is something like a thousand times that.

It took the spacecraft Voyager 34 years to even get close to it.

But then, the distance to our nearest star, Proxima Centauri, is over four light years away.

It would take Voyager 70,000 years to reach it.

And it's just the first of the 200 billion stars that make up our own galaxy, the Milky Way...

..which is just one of billions of galaxies that are millions of light years apart.

So how do you go about hunting for life on planets hundreds of light years away?

Once again, the transit is showing us the way.

FAINT WHIZZING SOUNDS

When I come to a place like this,

I get a sense of how small I am against the vastness of this landscape.

But it all pales into insignificance when I look up into space.

I'm utterly overwhelmed by the magnitude of the universe out there.

And I don't know about you,

but a little part of me always wonders, "Are we really alone?"

It's one of the most important questions to ask,

but one of the hardest to answer.

In recent years, we really seem to be coming to one of those points in history where things are changing

just like when Kepler and Halley worked out the size of the solar system.

But I really think we're closer than ever before to finding some answers.

I've come to Nevada far away from the bright lights.

It's the stargazing capital of the world.

You can't come to a place like this

and not be bowled over by the stars.

They are simply breathtaking.

And look, there's Venus, the brightest light in the sky,

and for me, a shining example of how far we've come in everything we've achieved.

But Venus is just a small planet that's relatively close to us.

In this patch of sky alone, there ar literally millions of stars.

So when it comes to looking for life out there, just where do we look?

Searching for stars is all very well

In the right conditions, they're easy to find.

But if we want to look for life, we have to search for planets.

And not just any planets. The right kind of planets.

Probably a planet very much like Earth - rocky, rather than a gas giant like Jupiter

But not only that, the planet has to be just the right distance from the star.

Not too far away...

..and also not too close to the parent star.

It needs to be just the right distance, so that liquid water can exist on the surface,

a habitable exoplanet.

The problem with finding these exoplanets is they are lost in the glare of the stars they orbit

So finding them is like looking for a flea crawling across a car headlight...

..from a mile away.

'Five, four,

'three, two...

'Engine start, one, zero, and lift-off for the Delta II rocket with Kepler

'on a search for planets.'

But recently, we've had a new tool to help us, a telescope in space - Kepler.

When a planet crosses between us and its star,

the light from the star dips by a fraction of a percent.

And it's by measuring this dimming that Kepler tracks down planets.

Kepler carries a photometer on board

that measures this tiny dip in light and it sends back a signal.

Now, it's not a picture or a message from the aliens.

It's this - a light curve.

And this may not look like very much

but this dip can tell us a lot about the planet that is in orbit around the star,

for example, how long it takes to orbit and what size the planet is

And using data like this, we can even work out the key question -

is the planet in the star's habitable zone?

In the last four years alone, Kepler has discovered 61 new planets

and there are more than 2,000 others awaiting confirmation.

Such a rapid rate of discovery makes this one of the most exciting fields of exploration today.

And these new techniques are not onl helping our search for planets.

They are also helping us hunt for ET

I've always wanted to come here to this eerie place.

These telescopes are very famous, but they're not telescopes that are looking.

They're telescopes that are listenin and they're listening out for any sign at all of a message from ET

a bit like an interplanetary telephone exchange.

This is the Allen Telescope Array, home to the SETI Institute,

a group of scientists who have dedicated their careers to searching for extra-terrestrial intelligence.

And leading the search is Dr Seth Shostak.

How do these telescopes actually go about getting data for you?

In principle, all you do is aim all these antennas in the direction

of some star system that, for one reason or another,

maybe just because it's a close star or a star known to have planets,

you think, "That might be a habitat for ET,"

then you just search over a wide range of the radio dial, looking for a signal at one spot on the dial.

It is a big universe out there. In our galaxy alone, there's 100 billion stars.

-How do you focus your search?

-We tend to look at star systems that are like the sun

because we know that a star system like the sun can have planets where you get intelligent life.

-We're here.

-We're here. We also tend to pick nearby star systems if we can as the signals would be stronger

and if you found something, it would be more interesting

to find nearby neighbours than somebody 5,000 light years away.

NASA's Kepler mission is now studying 150,000 stars, looking for planetary transits.

How has that technique helped your search?

One of the problems we had was that we're aiming these antennas towards the south

on the assumption that whatever star we're aimed at has a signal coming our way

that's arriving just at the right time, so it gets picked up.

It's like two cowboys aiming their pistols at one another and having the bullets meet in the middle.

-Across the vastness of the sky.

-I mean, it's not very likely.

But transits, the transit of the Earth in front of the sun,

as seen by ET, gives them a clock and they might be clever enough to say,

"Wait, what we'll do is broadcast a signal that gets to Earth just as it's transiting the sun."

OK? That way, they'll know where to look when, so the bullets have a chance of meeting.

This is where all the action happens, there is where the signals from the telescopes are brought in,

20 million channels a second being analysed. Tell me what happens here.

There's a whole room full of electronics and fibre optics and other hi-tech stuff.

And all the signals from all the antennas go in there.

They're sliced and diced and sampled

and, you know, some part of them is then sent to be analysed for signals.

What would the signal have to be lik to get you out of bed at three in the morning?

Nobody would call me unless the signal had the characteristics required to get me out of bed,

but it would have to be a very clean-looking signal,

a very narrow band and drifting at a rate that looks like it's not a transmitter here on Earth.

ET, yeah, I'll get out of bed!

It's utterly incredible to think that these images,

which amount to really nothing more than noise and fluff on the screen,

could ultimately be the first tantalising glimpse that we get of life elsewhere?

Yes, it doesn't look very dramatic, but that's the nature of discovery science and that's what we're doing.

A little plot like this with just a little wiggly, scraggly bit of brightening across it,

that's the clue that would tell us that there's somebody out there.

Seth's pretty bullish about his chances of finding ET

and actually, I think he's got reall good reason to think that way.

Kepler and the science that's coming out of the planetary transits

is really reviving and giving focus to his search.

If I was new to science today, I would very much want to go into this area.

There's so much data being collected about these planets

and we're learning so much about their size and suitability for life.

And I think that in the coming years we will find what we're looking for.

Transits have been crucial in helping us track down Earth-like planets.

But to find out if they sustain life,

we need to take the next step.

We need to get closer to these planets than ever before.

Close enough to peer inside their atmospheres.

To get a peek at the atmospheres of these distant planets,

I'm travelling as far out of our own atmosphere as I can get.

This is a bit of a bumpy drive,

but we're on the way to a really exciting place.

We're going to Mauna Kea,

one of the most famous observatories in the world.

It's also very, very remote.

I feel like I'm on top of the world

and I'm not far off.

There's very little air up here, compared with down on the ground.

I can feel it's quite hard to breathe.

All the weather, the turbulence down there,

all of that is underneath,

and that's why all these telescopes are here.

So this is an amazing place to come to get away from the Earth.

It's like a step on the way to the sky.

It's getting really cold here. The sun has just gone down.

But the telescopes are waking up.

There's a stunning sunset and we can still just see all the telescope flaps opening.

So as the view of the land fades away,

the sky is opening up and I can see Venus up there with my eyes.

But beyond Venus are billions of planets we can't even see,

and yet using these telescopes, scientists have developed an exciting new technique

to find planets with atmospheres that could support life.

And the most recent focus of their search is a new class of planets only slightly larger than our own -

super-Earths.

Now, all of these planets are just so far away. How do you study an atmosphere that's that far away?

When they pass in front of the star,

something very special happens.

The light from the star shines through the planet's atmosphere.

And as it does so, the light is absorbed at different colours by molecules

and each molecule has a unique fingerprint.

What are the chemicals that you're looking for?

The one that we're using as a key diagnostic right now is methane.

Here on Earth, of course, methane is connected to life processes.

We're really looking for life changing the atmosphere

in a way which can't be explained by any other process.

So you collect this data using this enormous thing here. How does that work?

This is the NASA Infrared Telescope Facility, a really marvellous telescope.

And the instrument my team uses a lo is the SPECS instrument back here, this blue one.

It works just like a prism. It break light apart into all these different colours, but mainly in the infrared.

And what's the most recent thing you've been working on?

This is a well-known super-Earth, GJ 1214b,

and what you're seeing right here is a preliminary spectrum

that our team obtained here at the IRTF with SPECS.

This is the feature we're out to try to confirm.

But how long are we going to have to wait until we can really look inside a planet's atmosphere

and answer the question about whether there's life there?

That's a question I think we will get to over probably the next 10 to 15 years.

Within my professional life, I expec we will have answered it, but there is still a lot of work to do.

I find the measurements that they're making here absolutely astonishing.

The subtlety required to detect an atmosphere from this far away is just amazing.

Science fiction writers have been inventing crazy planets for decades

and now we know they really exist.

And it makes the sky for me a completely different place.

Studying the atmospheres of distant, transiting planets

is some of the most exciting science happening today.

But precision is everything and to be as accurate as possible,

we need to know if we're doing things right.

And that's what's happening tonight with one very special telescope 350 miles above us -

Hubble.

So what are you hoping to achieve with tonight's transit and Hubble's observation of it?

We hope to retrieve the atmospheric signal from Venus

and to do that, we will observe the transit of Venus with a spectrograph

So a spectrum looks something like this.

It basically tells you what's inside the atmosphere of the object you are studying.

But we already know the atmospheric composition of Venus, so why are you doing this?

Well, the idea is really to be able to test our technique to study the atmosphere of exoplanets.

We want to use Venus as a template, as a model.

So, basically, you're testing that your method is correct

and if it correctly splits up all the components of Venus's atmosphere,

you can then apply it to exoplanets far away that we haven't analysed yet?

Yeah, with much more confidence than we would have without doing this experiment.

But it's not quite as simple as just focusing the Hubble telescope on the transit, is it?

No, actually, it's forbidden to point Hubble to the sun because it could damage the instruments,

so we are going to use a trick which is pointing at the moon.

In other words, we are going to use the moon as a giant mirror.

It just seems like such a huge undertaking

and there's only one chance in your lifetime to get it right.

This is a unique opportunity to record the transit of Venus with Hubble.

-Does that make you a little bit nervous about getting it right?

-More than a little bit.

-Really?

From the first transits we witnessed

to the one that's happening tonight,

the transit of Venus has transformed our understanding

of the vast universe we belong to.

It's given us the size of our own solar system

and now it's helping us to take giant leaps into distant space

in our search for life.

It's meant so much to so many people

and tonight is no exception.

I'm going to watch it with my kids.

This is kind of a way I get to share with them a little bit of what I do and the excitement of astronomy.

I'm excited to be going to Svalbard.

I'll meet the Venus Express team there and we'll see the transit together.

Hopefully, somewhere up on the mountains for the best view.

During the transit, I might actually be in bed trying to get some sleep

because the real work for me starts after it.

During the next transit of Venus, I'll get some of my colleagues together, we'll have a big party,

haul out our telescope, put a solar filter on it and watch Venus pass across the sun.

After all, we won't be around the next time this happens.

And if you want to enjoy this spectacle safely,

you don't even need a telescope. It's something everyone can share.

Now, there are lots of ways in which you can take part,

but there's one thing that you must keep in mind and that's never look at the sun directly.

It gives out a lot of light and heat that would damage your eyes without you even realising.

By far the simplest way to view the transit is by using a filter,

so, for example, one of these, and they're extremely easy to use.

All you have to do is put them up in front of your eyes and then turn to look at the sun. Let's give it a go.

Wow! What does it look like to you?

Green.

Green?

Now, Venus is only one-thirtieth of the size of the sun,

so you'll have to have pretty keen eyes to see the transit.

-Do you think you'll be able to see Venus?

-Yeah.

-You'll give it a go?

If you want to project an image of the sun that's bigger, you can us a telescope like this one

and you should never look through the eyepiece.

Instead, project the image of the su on to the card like we have here.

Hold it just underneath the telescop and what can you see on here?

I can see quite a lot of sunspots and there's quite a large one.

-This one is massive.

-Yes.

-Using this kind of technique makes the sun much, much bigger.

-Do you think you'll be viewing the transit?

-Yeah. It's going to be exciting.

-SHE LAUGHS

-Yeah.

-Absolutely beautiful.

-Yeah.

I look at the moon quite a lot through binoculars.

You're a bit of a pro at this, aren't you?

Wherever you're watching it,

this is going to be a spectacular event.

There's just over an hour to go before Venus makes its first contact with the outer edge of our star.

And I absolutely cannot wait to find out what this transit teaches us about our incredible universe.

And since this is the last transit of Venus until 2117, make the most of it.

Be a part of this rare moment in history.

And remember, the next time you look up at the morning star,

just take a moment to consider how remarkable it is.

# I'm wishing on a star

# To follow where you are

# I'm wishing on a dream

# To follow what it means

# To follow where you are... #

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