Venus and the Midnight Sun The Sky at Night

Good evening.

In this very special programme, we're going to talk about something

that won't happen again for over 100 years, so make the most of it -

this is a transit of Venus.

If you know, there are two planets closer to the sun than we are -

Mercury and Venus.

And when they pass in transit,

you see them pass across the sun as black spots.

The great astronomer, Copernicus,

realised that the planets go round the sun.

What he didn't know was how far away they were

and what astronomers wanted to do was to measure

the distance between the Earth and the sun, and that was far from easy.

They had to wait for a transit of Venus.

With seeing the last one, you couldn't see it well from here

you could from the Arctic island of Svalbard

and that's where three of our Sky At Night team went.

So, over to Chris in Svalbard.

The archipelago of Svalbard

is a starkly glamorous part of the Arctic Circle.

78 degrees north of the equator,

home to eider ducks, polar bears

and the town of Longyearbyen, it's a magical place.

In winter, the sun never rises here

but right now, in summer, the sun never sets.

This is the land of the midnight sun, which is just as well,

because we'll need that to see the whole transit.

It begins just after midnight local time.

The weather's not too bad for this part of the world.

I really hope it stays clear because the next transit doesn't happen

until the 22nd century, so this is really my last chance.

I've never been this far north before.

Svalbard is, after all, not that far from the North Pole.

It's already been quite an adventure getting here.

The sun remains at the same height above the horizon throughout the day,

an effect that feels distinctly disorientating

to those of us from more southerly climes.

Lucie Green and Pete Lawrence have joined me on this quest.

It's the night before the transit and we're going on a voyage with

a team of European scientists who work on the Venus Express mission.

Venus express has spent the last six years studying Earth's evil twin,

trying to work out why Venus is quite so different from our own world.

Amongst those trying to solve its mysteries is Colin Wilson,

who helped set up this extraordinary trip.

What's happening tomorrow is that Venus is going to pass

directly in front of the sun and this is an incredibly rare event.

It happens... The last one happened in 2004.

The next one after this isn't going to happen until 2117.

And also to illustrate how rare it is,

the last ones before that weren't since the 19th century.

It seems each generation of astronomers

lucky enough to see a transit has their own reasons for observing it.

For us in the 21st century,

it's a chance to test methods we might use

to study the atmospheres of planets which orbit other stars.

Planetary transits are the only way we have of characterising exoplanets.

These are planets discovered around other stars,

of which we've discovered hundreds in the last decade.

We've discovered them because, in some cases,

-they go in front of their star?

-Because of transits.

But then once we know the planets are there,

these exoplanets, we try to characterise them.

We try to think, does it have water? Does it have oxygen?

Could it be conceivably a nice place to live,

or where someone may already live? And to study that,

the only technique we have is planetary transits.

Here, we have a very rare event which is

a transit of an Earth-like planet in front of a sun-like star,

and once we've done that analysis,

we can actually look up the right answers,

because satellites like Venus Express are giving us

the detailed composition and we can tell

whether the transit analysis has been right.

Colin and his colleagues may be here for astronomical reasons,

but the boat trip's also a chance

to see the magnificent scenery of Svalbard and even spot some wildlife.

There he is!

Well, it's a beautiful evening up in Svalbard, a beautiful location.

What do you reckon, Lucie - not a bad place for a transit?

This is absolutely perfect.

We've got fantastic clear skies at the moment, which bodes well

and you know, it was quite a journey getting here,

so I'm full of excitement

and I can't wait to see how the sun looks in terms of the sunspots

as well as seeing the black disc of Venus moving across as well.

Of course, we're here

because we need to see the sun just after midnight.

The sun is up for the entire day and all night.

It's 7:30 at night and the sun's still up there. It's pretty nice.

-It sinks to about 10 degrees above the horizon.

-That's right.

Pete, you've been doing some careful observation of the conditions.

What did you make of your day here so far?

Well, in the morning, I was actually quite depressed about things

because there was thick cloud everywhere

and there was no wind, so nothing was moving.

Then suddenly, as if by magic, it just disappeared completely.

I got the telescope out, tested the telescope and I actually managed

to find Venus, which is really close to the sun at the moment.

We're not very many hours before the transit and I now feel at home.

We also have to worry about seeing, about how crisp the sky is.

I really wouldn't worry about that.

The scene this afternoon was amazing. Venus was absolutely crisp.

The atmosphere looks really, really steady,

so long as the clouds stay away, and we've got no guarantee of that,

but fingers crossed they do, we should have a fantastic view.

-We're looking forward to the transit, you're looking forward to your sunspots.

-Yeah.

You've got some work to do before the transit, Pete,

you've got some images you want to get before Venus hits the sun?

I'd really like to try and get Venus about a degree and a half

away from the sun, which is really, really close.

That's probably about 24-30 hours before the transit actually starts.

If I hit it right, what happens is,

where Venus looks like a crescent...

It's a crescent when it's further round and then as it gets closer...

..as it gets closer, the cusps of the crescent start to elongate round.

If you get it at the right point,

which is dangerously close to the sun, those cusps join up

and you get a ring, which I'm really looking forward to seeing.

This is light being refracted in the atmosphere of Venus.

It's scattered round the upper part of the atmosphere.

-It's just creating this amazing ring effect.

-I'm looking forward to it.

Tonight, I'm going to enjoy the boat trip, see a bit of Svalbard,

and our surroundings and if the weather's like this tomorrow,

then I will be deeply, deeply happy.

I think I'll be happy too.

We're not the first to travel for a transit of Venus.

Previous generations have scrambled to the far ends of the globe

whenever these rare events come round.

We've just come to a grinding halt. We've hit some ice.

Feels appropriate, given the hardships and struggles

that the previous transit expeditions went through.

Our boat journey comes to an end

exactly 24 hours before the transit,

with brilliantly clear midnight sunlit skies

making Longyearbyen look rather tranquil.

I feel rather less calm, it has to be said.

We need these clear skies to last until tomorrow.

This will be only the seventh transit of Venus ever observed

and the reason transits are so rare

stand to a little bit of celestial mechanics.

To get a transit we need the sun, Venus and Earth

to be exactly in a straight line.

That doesn't happen every day. It needs a special set of circumstances.

The solar system is dynamic

and Venus, being much closer to the sun than the Earth is,

orbits more rapidly, taking only 225 days to do one lap.

Whereas I over here for the Earth take, of course,

a whole year to go round.

In fact, I only catch up with the Earth after 584 days.

And you'd think that there'd be a transit every 584 days?

But that's not actually what happens.

When we look at the orbits of Venus and the Earth

we see that they're tilted with respect to each other

by just over three degrees

and that means that even when this alignment happens, sometimes

Venus passes underneath the sun from the Earth's perspective

and at other times, it's moving above the sun from the Earth's perspective.

In that case, a transit doesn't happen.

So all of this only comes together very, very rarely.

In fact it happens twice, eight years apart,

separated by a gap of more than a century,

so that's why we have to wait so long for the next transit of Venus.

By the 18th century, astronomers were making incredible efforts

to trace transits of Venus.

Their aim was to get observations of the transit from all over the world.

One famous expedition was led by Captain Cook,

and they observed the transit from Tahiti in 1769

before they ran into Australia on their way home.

By timing how long it took for the planet Venus

to pass in front of the sun, astronomers realised

they could measure the sun's distance from the Earth.

Observing the transit was therefore a high scientific priority,

but once mixed in with efforts to improve navigation,

it also became a matter of national prestige

as scientists to persuaded

governments and navies to lend them a hand

as well as plenty of funding.

Lucie and I took a trip up the hill overlooking Longyearbyen

to talk about the successes and the failures of previous transit expeditions.

I feel like we've had quite a trek coming up this beautiful mountain.

Really, it's nothing compared to

the lengths that the previous transit expeditions went to.

I think we've done pretty well. We've come all the way up to the Arctic.

You're quite right, of course.

Particularly the 18th century transits, when they were trying to use

the transit of Venus to measure the solar system.

They sent observers right across northern Europe

to try and get as many observations as possible.

For example, the Swedish Academy of Sciences

sent people up to northern Sweden.

The French Academy of Sciences, who were behind a lot of the efforts

to try and co-ordinate these observations

sent somebody off to the Russian Siberian wastes

and he had a particularly terrible time, because it was spring

and he was trying to get to his observing site as everything melted

and of course, that's not very good if you're travelling by sled.

And so, he ended up having to get his local crew drunk to get them to

go across the last of the rivers with the ice cracking underneath them.

But he made it and so we have observations from Siberia,

observations from northern Sweden.

What we don't have and we really needed were observations from India.

In particular, there was a Frenchman called Le Gentil.

Ah, the unluckiest astronomer of all time!

He is. He set off in 1760 to see the 1761 transit.

He gets attacked by the British.

The world was at war at that point, it was the Seven Years War.

They only escaped because of fog.

He makes it to Madagascar, doesn't make it to Pondicherry,

the French colony in India because of the war.

In fact, the British have taken it.

And so, he ends up on serving the transit of Venus from the deck

of a ship, really rather poorly.

Which of course would be moving all the time.

Exactly - no good for precision observations.

But also, they need to know where on the Earth they are

and he can't get good measurements as to where the ship is.

And so, he decides, quite sensibly,

that instead of going all the way back to France,

he's going to hang around for the 1769 transit.

He waited for eight years,

which when you go to those lengths, I suppose you might as well do.

The whole month before the transit was beautifully clear.

Gets up every morning and it's clear skies

and then on the morning of the transit,

he writes in his journal that he woke up about two in the morning,

he could hear the wind whipping in off the sea

and he knew that that meant clear whether.

But, as you know, he wandered outside and looked up

and it was completely overcast.

And then he comes back and describes throwing himself face down

onto the bed and he writes, "Such is the fate of astronomers."

And in fact, he went mad.

It is amazing to think that at the time

when we didn't know the size of the solar system,

we also didn't understand the Earth, we didn't have a map of the landmass

and even know how to get accurate positions on the Earth.

They did get observations, particularly 1769,

from all over the place.

It turns out one of the limiting factors that stopped them getting a perfect measurement

was the fact they didn't know the distance between Greenwich and Paris.

Some observers reported where they were relative to Paris,

some relative to Greenwich,

and that fundamental measurement wasn't made till much later.

Of course, you needed to know the separation

to put that into the calculation for the sun-Earth distance.

Absolutely. Without that, then all of this effort,

all of this trekking round the world is wasted.

Then there's also the other thing that affected them,

-which is this black drop affect...

-The problems of the transit.

That's right, this elongation of Venus when it's inside the sun,

which means making the measurements,

the crucial timing measurement, is incredibly difficult.

We know from Halley that you need to get a measurement to within about

one second of time in accuracy to get a good sun-Earth distance.

The interesting thing is if you took what we know about the Earth now,

we know the distance between Greenwich and Paris

and we know where the observers were,

if you take the measurements they made and that knowledge,

you get a pretty good value for the distance to the sun.

The best ones were within 1%

of what we know as the sun-Earth distance now, which is incredible.

-Good going.

-Incredible, that's right.

This is only the seventh transit to be witnessed by humanity,

but we've come so far from working out the size of the solar system

to looking for life elsewhere in our universe.

Well, first of all, let's hope we see it.

Well, I'm beginning to understand just how Le Gentil must have felt,

because the clouds have rolled in.

The sun is now completely obscured, leaving us more than a little worried

about the forecast for tomorrow's transit.

Inspired by the plucky astronomers of the 18th and 19th centuries,

we could do nothing but grit our teeth and hope for the best.

While we wait for the skies to clear,

we've set up our very own transit up here in the snow.

Transits occur whenever there are three bodies in a row.

So we've got the Earth, we've got a purple ping-pong ball

pretending to be Venus, and then of course, we've got the sun back here.

But what you see during a transit depends on exactly where you are.

The observers on the Earth

experienced an affect known as parallax,

which means that observers near the North Pole

see Venus in one position against the disc of the sun

but you'll notice that towards the South,

Venus appears in a different place against the face of the sun.

And so with that measurement, they only needed to know one more thing -

they needed to know the relative distance from the sun, out here,

to Venus and then from Venus back to the Earth.

And that's something that had been known since the 1600s

thanks to the work of Kepler, who realised that

the orbits of the planets around the sun had a special relationship

-to how far each planet was from the sun.

-And so that was it.

With those two measurements, the speed the planets were moving

and the observations of the transits, the observers were able to set out

the scale of the solar system for the very first time.

There are only two planets which transit the sun as seen from Earth -

Venus and Mercury.

Let's go back to Patrick to hear more about these two enigmatic worlds.

Time now to talk about the inner solar system.

With me are Chris North and Paul Abel.

These planets are very different, so let's begin with little Mercury.

Yes, I have it here. The usual sky at night model..

Wonderful little Mercury.

In fact, Mercury, one of the ancient planets known since antiquity,

earliest cavemen must have seen it whizzing around in the sky.

We had to wait till the start of the telescopic area before we could

begin making investigations of it.

Even then, we didn't see an awful lot.

-We didn't really know much until the space age?

-That's right.

The reason being, of course, Mercury's very small

and it's very close to the sun,

and this makes it very difficult to observe.

Schiaparelli, of course, made lots of observations of it.

We had to wait until, was it Mariner 10 got out to Mercury first?

Yes, Mariner 10 went round it, passed it by the 1970s,

made the first observations. One of the problems with Mercury is that

it's so close to the sun that if we send a spacecraft there from Earth,

it's a third of the distance from the sun

and as the spacecraft goes inwards,

it gets faster and faster and faster,

which means that it whizzes past Mercury,

so the biggest problem with going into orbit around Mercury

-is actually slowing down enough.

-Yes.

So the Messenger spacecraft had a very convoluted journey

to actually end up going into orbit around Mercury

and is the first spaceship ever to go into orbit.

Everything else, Mariner 10, just passed straight by.

So, up next then, the planet Venus. Now, this is an interesting world.

It couldn't be more further removed from Mercury.

Shrouded with a very thick, poisonous atmosphere. Lovely, bright object.

It's a beauty. Go there, you'll find it anything but beautiful.

Indeed. It's more like hell.

It's an interesting planet for observers to look at.

It's very, very bright and the reason it's very bright is because

the vast clouds covering it reflect a lot of sunlight.

This means that the early telescopic observers that looked at Venus

didn't see an awful lot,

so Venus became a mystery. I think we had to wait again till

the spacecraft got there, because there was very little we could do.

With the space age, we've had probes that have actually gone to Venus.

The earlier probes were squashed on the way down?

-They were, yes.

-They didn't make it to the surface.

The pressure on the surface of Venus

is 90 times the pressure on the surface of Earth,

so they had to build the spacecraft again

to try and survive the pressures. They got to the surface

and discovered the temperature on the surface is 400 degrees.

The longest a probe survived on the surface was

Venera 13 in the 1980s, I think.

That sent back that lovely image, one of my favourite ones,

a little bit of glowing sky.

That lasted for 127 minutes, that's just over two hours.

Finally, its electronics overheated.

-I think we can forgive it for that.

-Well, yes!

-I wouldn't like to survive in that kind of in environment.

-No, I wouldn't.

To make it worse, the atmosphere is very dense, the surface is very hot,

and you have sulphuric acid clouds to contend with.

We've had probes go there, so we had the Magellan probe in 1990,

which made a radar map using radar that can penetrate

the very thick clouds

and was able to map the surface and show us mountains,

volcanoes, in fact, possibly or probably not active,

certainly not very many of them active,

and valleys and so on and lava flows.

Very interesting structures on the surface as well.

There are sort of pancake shapes, a very, very weird surface.

All kinds of volcanoes.

Yes, it's a very volatile world on the surface to look at

and it helps that the maps are always drawn in that sort of

orangey-yellow colour, which makes it look very hot.

Whether any of the volcanoes are active now,

well that's a matter for debate.

-A great debate.

-It is.

We know that a few hundred million years ago,

there was an enormous resurfacing of the surface of the planet

due to this immense bout of volcanism which plagued the surface,

and it's possible that Venus undergoes such bouts, you know,

-in periodic cycles.

-It would certainly explain why

the surface appears to be all the same age.

It's actually all very young. If we try and count the craters

on the surface of Venus, we actually see there are very few,

only about 1000 on the entire surface.

And over a whole planet, that's not very many at all.

Partly that's because it's been resurfaced and partly

because the atmosphere burns up the smaller objects that hit it.

Both Mercury and Venus are inferior planets, they are closer to

the sun than we are, and from our point of view, occasionally

they pass in front of the sun in an event known as a transit.

The best place to study the sun is in fact from the very

northern climes of Europe, in Svalbard.

And the team, Chris, Lucy and Pete, have been there.

So, back now to Svalbard.

'The Sky At Night team has come to the Arctic Circle to see

'the transit of Venus, which is happening later tonight.'

Down in Longyearbyen, Peter has been on an expedition

to find a good spot to observe the sun

and get an elusive shot of Venus as it approaches it.

Well, I brought lots and lots of kit over from the UK

to see the transit of Venus from Svalbard.

Now, the transit is going to occur in a number of hours' time,

but before that actually happens, there are other things to look at.

I have been following Venus over the last few days from the UK

and watching that beautiful, slender crescent get thinner

and thinner and thinner.

Now, as it gets really close to the sun,

the cusps of the present begin to extend around and

if I am really lucky and if I can find it today, I might be able to

see them join up to create a ring, which is the atmosphere of Venus.

Now, that should be really quite special,

so I'm really very excited about that.

Venus guards its secrets well.

In a telescope, it looks so lovely, mysterious and welcoming.

But its thick, impenetrable atmosphere

is full of carbon dioxide and sulphuric acid,

a most uninviting world.

Venus and Earth are almost the same size,

but that is where the similarities end.

It rotates much more slowly and spins backwards.

It also lacks a magnetic field.

Earth's magnetic field protects us from damaging particles

from the sun and from space, and a nice bonus is the Aurora Borealis.

In winter, Svalbard is a great place to see the Northern Lights.

It is a sign that the magnetic field above is acting as our shield.

What I have here is a magnet

with a north magnetic pole and a south magnetic pole

and iron filings around the magnet, so if you look carefully,

you can see that the iron filings

take on what is actually the shape of the magnetic field

and they form these beautiful arches going from one pole to the other.

You can see here, they're in arcs, right?

So, this is a pretty good model

-of the Earth's magnetic field.

-That's right.

And it's nice, because this is three-dimensional

so you can see the magnetic field forms a sphere

and the magnetic field lines shown by the iron filings

go in at the north pole

and the south pole, which is what we have happening around us here,

for the huge Earth's magnetic field.

If this is inside Earth, we're here in this

-cluster of iron filings at the top, near the poles.

-That's right.

So, this is the shape of the Earth's magnetic field,

-sitting in the solar system.

-So, when you have the solar wind,

those particles coming in towards this, they get channelled

down towards the poles, that's how you get the Northern Lights.

That's right, and it becomes very clear to see why that's the case.

The particles coming from the sun can get on to

the Earth's magnetic field lines, and if they do that,

they can be funnelled down, and they naturally get funnelled to the

polar regions because that is where the magnetic field is guiding them,

the field acts as this kind of tube, along which the particles can flow.

So, here on the Earth, this invisible magnetic field above

our heads protects us from the solar wind and that is really important.

But on Venus, there is no protection at all.

Without a magnetic field, Venus has no way to stop the solar

wind from constantly bombarding it, stripping away its atmosphere.

We think that billions of years ago, Venus was once a wet world.

'And Dr Janet Luhmann talked to me about why

'she thinks the lovely Venus became the Earth's evil twin.'

Well, Venus is special

and different than the Earth in that it does not have

an internal magnetic field.

And so, there is nothing to prevent the solar wind from directly

-entering the upper atmosphere.

-Slammed straight into it.

Slammed straight into it like a comet,

and a very long time ago, science fiction writers

thought Venus was a very large comet and presented it as such.

When we finally visited Venus with spacecraft

and took detailed measurements, we of course proved

to ourselves once and for all that Venus is very much a planet.

One of the things that has been a puzzle is the lack of water on Venus.

And what happened to it in the past.

So assuming Venus began in a very similar state to the Earth.

Exactly.

Whereas Earth in its oceans has in the order of a kilometre

equivalent of water if you spread the oceans over the globe,

on Venus there is only a few microns of water in the atmosphere.

And so, that and the particular composition of hydrogen

in Venus's atmosphere, which is unusual,

combined with the oxygen loss that we see, suggests maybe water has been

stripped off the top of the atmosphere

over the 4.5 billion year lifetime of the solar system.

The main question is whether it occurred in a much stronger

fashion early in the solar system's history.

It feels like Venus has been overlooked in recent years,

it has become the evil twin or the ugly sister.

But actually, there is still a lot of exciting things to find out.

Exactly. And in fact, it is the twin Earth,

from early observations of its similarity in size,

and it is the most proximate planet, it's closest to us.

And yet, all our attention has been

focused on Mars, in part because we can actually go to Mars

and rove on the surface

and photograph it in minute detail, in all wavelengths, essentially.

On Venus, we have this shrouded body,

with incredible pressures on the surface that would crush most

equipment and of course would be totally unfriendly

and inhospitable to anything resembling life as we know it.

And now, it is good to see that there is some attention

being refocused on Venus.

In space, the LASCO telescope is looking at the sun

and we can see Venus marching towards its edge.

Just as it was getting dangerously close,

Pete did manage to get his Venusian ring,

created by sunlight being deflected off the top of the atmosphere.

It's really rather beautiful.

It's 11 o'clock at night here in Svalbard,

the transit of Venus festivities have begun.

It is still light, as you can see, which is great.

It's also pretty cloudy, which isn't.

There are a few breaks in the clouds, though,

so we haven't given up hope yet.

But whatever happens, in about an hour from now,

the last transit of Venus of the 21st century will have begun,

whether we are able to see it or not.

Most of Svalbard is here

and the locals are getting into the spirit of the occasion.

The longer we are here,

the more I begin to sense what life in this frontier land must be like.

Previous explorers who have travelled to see the transit of Venus

found all sorts of things, so I pretty much imagine this is what

those arctic explorers encountered, back in the 18th century.

THEY SING IN NORWEGIAN

What I have here is the low-tech way of watching the transit of Venus.

This is a simple solar viewer.

The light comes in through the glass at the front, bounces off some

mirrors on the inside and then down through a lens and it projects

an image of the sun a few inches across on a piece of paper in here.

So this is a really simple and really safe way to

look at the transit of Venus, and I should be able to see

the event happening really clearly with this piece of kit.

But also, using this, I can see sunspots

that are on the surface of the sun.

And I know at the moment, there are some really fantastic

sunspot groups, so I'm looking forward to seeing

just how close Venus gets to those.

The skies are still ominously heavy, but Miguel and Michelle

from the European Space Agency have set up their telescopes nonetheless.

They will be sending images of the transit live onto the web.

But only if those clouds clear.

Also here are the Venus Twilight Experiment,

a global collaboration in the best tradition of transit hunting,

with teams in Japan, in Hawaii, in Kazakhstan

and even in Ulan Bator in Mongolia.

All of these teams are waiting to catch something called

the arc of Venus, or more scientifically, the aureole.

It occurs when the sun's light is seen shining directly through

the thick Venusian atmosphere, rather than being reflected by it.

And it occurs for just a few fleeting seconds, around the beginning

and the end of the transit.

There will be a sort of ring of light around Venus,

which is fantastic to see.

We have great expectations of how beautiful this should be.

It is mostly visible during what we call the first contact,

which is when Venus hits the sun, and the second contact,

when Venus is now fully plunged into the face of the sun.

So, it is a matter of 15 to 20 minutes.

The arc of Venus was seen during the 2004 transit,

both from the trace spacecraft and by amateur astronomers on the ground.

Remarkably, we can even see detail in the arc,

revealing the layers of Venus's atmosphere.

In 1882, there were only visual and some photography,

but the photography did not see the aureole.

Only drawings by expert observers mentioned this aureole.

It was also mentioned in the 18th century,

even since 1761 and 1769.

The telescope works by blocking out the sun

so that the delicate arc of light can be revealed.

But setting it up in Svalbard has been tricky.

We wanted to observe from here

because this is the only part of Europe that can actually see

both ends of the transit - the ingress,

when Venus comes into the sun, and the egress, which is the opposite.

And for that, we had to use portable equipment, because there is

no major astronomical facility here, no fixed facility.

And this is also something which is difficult for any astronomer,

to align a portable motorised mount.

You always need to aim at the pole in a very accurate manner,

and this is the midnight sun period of the year,

so there are no stars at all, so this is difficult to do.

It's nice to see that the French

and the British can set up next to each other without war breaking out!

A little bit different from the 18th century.

But we do still share some problems with that

unluckiest of astronomers, Le Gentil.

After all, the thick clouds are still hanging about

and time is beginning to run out.

Look, I'm not a natural optimist. But that looks much like it did

just before we got that clear patch, half an hour ago.

-Well, if it does go, it's going to be a real rush.

-I think that's...

Do you see what I mean? I think that's breaking,

in between the different bands.

We might just get a crack. That's all we need.

I don't actually know where the sun is up there at the moment,

but those rays in the distance, they are pointing back to it.

-That's right... Really? Has it moved all the way round?

-It has, yeah.

-We'll be waiting a while.

-I'm probably wrong, then.

It's so bizarre, because we're now coming up to midnight,

and it's daylight.

-It is, which is good.

-For a transit, it's excellent!

This is the thing, for transit of Venus explorers,

we are in the right place at the right time, with our equipment.

-Well, we can't control the weather.

-We can't.

The transit will be a long affair, lasting nearly 7 hours.

But the beginning and end are dramatic.

The tension is running high.

Getting another glimpse of the sun coming out.

But not the full disc.

Will it be enough for Pete to get his telescopes lined up?

I don't think so.

It's such a tease!

Lucy, you were telling me that you wanted to see something

called the black drop, which you only see on the way in and out?

That's right, this elongation of the disc of Venus

when it's close to the edge of the sun. Since the last transit,

people have put forward an explanation for that.

I want to see it myself, and then later on see

-other people's opinions.

-The sun is right there, isn't it?

We've got a few minutes to go, come on!

We've flown all this way, we've brought all this kit.

It could do it, actually.

I'm going to change tack, I'm going to go to white light now.

-OK.

-And have a look. I'm going for it.

-Do we need to get out of your way, Pete?

-No, you're fine there.

Patrick tells a story of an eclipse in Finland where

he was the only person to leave his kit.

-I know, and he was the only one that got the picture.

-Yes.

You've got to be optimistic, haven't you?

You just don't know what the cloud is going to do.

-No, it's just thin enough to give us a little bit of hope.

-Yeah.

And this telescope will track the sun?

-It will, if I can find the sun first!

-Once we're locked on.

Well, somebody locally predicted the clouds would clear at midnight.

But also, according to Ian,

they were sitting on their porch with a beer

-when they predicted that, so...

-That can make you more optimistic!

'This is astronomical torture. Goodness knows how those

'who had staked their career on transit observing must have felt.'

-Well, about two minutes left.

-It's not looking good.

It's not, my optimism was there for a second, it's faded already.

Mine peaked for about 30 seconds, now it's gone.

There's a higher level of cloud that's come in that wasn't there,

literally wasn't there half an hour ago.

It's really grey. Really, really grey.

The sun is just there, near that gap in the clouds.

-We've got the telescope, so we just need...

-Oh, is that the sun's...

-No, it's not the sun's disc, is it? Is it?

-Is it?

That could... No, it's too far over.

-Yes, it is.

-I'll go with anything.

-Yes, it is, it is.

-It's too round.

Is it? Yes, it is. There's the sun.

Pete, well spotted. Two minutes to go.

-OK.

-This would just be the most magical piece of timing.

-Come on!

-Oh, my goodness, come on!

It's not bright enough to register through the filter.

-A minute and a half to go.

-It's about to brighten, Pete.

-We've got the top bit as well.

-Is that where it is?

Yeah, it comes in across the top.

< PEOPLE SHOUT You're already aligned. I think some people over there have got it.

Literally 20 seconds and the sun's just come out.

I think some people over there have got it. We've heard some gasps.

We can see the sun. Can Pete get his telescope on it, though? That's the question.

-It's going to disappear again.

-Oh, come on!

SHE SPEAKS IN FRENCH

'A clear patch in the right place at the right time

'and Pete gets his first shot of the transit of Venus.'

Pete, I can't quite believe we've got this, and I won't distract you too much,

but just at the point where Venus started crossing the sun,

we've got a clear patch

and there is the last chance you'll have for 105 years

to see Venus beginning to cross the face of the sun.

Even though the clouds are there, it still sends tingles up the back of your neck.

-It's dramatic with the clouds going past.

-Yeah, definitely.

Proof that the solar system is working.

There's a sunspot in the top-left as well.

There are loads of sunspots on there

which is quite photogenic. It's like the sun is a canvas

against which the transit is taking place.

-That's very nice.

-Yeah, I thought so, too.

'Venus has begun its long crawl across the sun's disc,

'a majestic demonstration of the power of celestial mechanics,

'but we are still at the mercy of nature.'

If the clouds weren't here, we should be seeing Venus now,

just passing over the edge of the sun.

We've had first contact, and in a few minutes' time,

we'll have second contact,

-so maybe we'll catch that one.

-Lucie!

-We've got it!

-Oh, I'm missing it!

It's actually behind some thick cloud.

-It's just about there.

-Oh, yes, there it is!

-It's moving quite quickly onto the disc, isn't it?

-Wow!

-Incredibly fast.

-It's maybe halfway there now.

My goodness...

So we've got ten minutes now until second contact?

-That's right. When Venus is completely on the sun.

-Fully inside, that's right.

We can see if we can see the infamous black drop.

-It's very black at the minute.

-It doesn't exist.

'Previous observers reported that something strange happens

'as Venus moves onto the sun's disc.

'It seems to stretch, forming the infamous black drop.

'We'll have to wait and see if the black drop is real.

'For now, I'm with Pete, a sceptic.'

It's like if you hold your finger and thumb up

and you have them close to you. As you put them closer together,

it looks like your finger and thumb begin to join together.

-Yeah.

-That's one theory.

-And in bad optics.

-Yeah.

-You've got a little layer of heat between your finger and thumb,

and I think that distorts the view.

Yes!

Everyone is just ecstatic

that after our long wait, we're finally getting a glimpse of Venus.

These are some of the first views from spacecraft looking at the sun.

In these amazing time-lapse movies,

we see Venus entering the sun's disc, with all its dramatic texture,

in breathtaking detail. It's both beautiful and astounding.

The transit's officially started now.

We can actually see it from Svalbard.

Only an hour late, but that's pretty good!

Look at that! Isn't that spectacular?

That big black circle.

-It's so clear.

-Have you seen this?! It's got all the ridges in it.

It does.

You can see the disc really clearly. It looks terrific.

It's really clearly defined.

'It's touch and go at the minute - one moment the sun's there

'and then it's gone, but we've still seen it.'

I think we should settle in for the night, guys,

-cos that's gone behind a very large bank of cloud.

-Definitely.

So, transit is underway. We saw some of it,

so mission accomplished, as far as I'm concerned,

-and now everything else is just gravy, don't you think?

-Yeah, definitely.

Gentlemen, how is it for you? How's it going?

-It was stressy...

-Stressy, yeah!

..because we can do nothing automatically,

-so we have to do it manually.

-Because of the clouds?

-Because of the clouds.

This means that we have to adjust the cameras, the setup,

for every shot.

-But you've managed to see something?

-Yes, and it's so exciting!

We had to take the filter out, in fact,

so that we could see the image of the sun

through the clouds. So the cloud was the filter.

'Looking at the sun is incredibly dangerous,

'so do always use filters or project its image

'and be very careful with the telescope.'

How are you doing so far? Have you seen anything?

Well, I saw quite a nice view in the beginning,

for a glimpse of both the sun and Venus,

and then we had some clouds.

I swapped the eyepiece to the camera and I made some shots.

I think I got a couple of good things.

-So you've seen the transit?

-I've seen part of it.

-Mission accomplished.

It's going great. We've got the live feeds from the guys here,

and also their colleagues in Canberra,

which we're keeping an eye on.

-Clear weather in Canberra, by the look of it.

-There's some cloud, too,

-but there's Venus down there.

-Excellent.

I've just taken a nice shot of the transit

through our ESA TV cameras there.

-Very good.

-We've got a video camera there as well.

-And going straight out on Twitter?

-Yeah, and retweeted around the world.

That's probably a first. This is live tweeting of a transit for the first time in history.

-That's probably right. That's amazing.

-There are always firsts.

'Some news from the Twilight team -

'no luck in Svalbard,

'but they've heard from Arizona that there's been a successful observation

'of the arc of Venus.'

The report I just received says that they observed the aureola very well.

It was quite bright, very asymmetrical, as expected.

Which is what you wanted, cos that's the interest.

And it was more intense near the pole.

Moreover, it was also observed well before the first contact...

-Oh, great.

-..which means we'll have a long photometric curve

on each of the points on the Venus atmosphere.

This is what we want

because the longer the light curve is for each point,

the best constraint we have on the temperature

-at the point we try to measure.

-Ulan Bator? Have you heard from them?

No, but I think they don't have fast internet there,

so I don't expect them to call during the transit.

So we've got the sunspots that we can see really clearly.

-Oh, yeah.

-A variety of sizes

and a real cluster of them, actually.

-There's an enormous number there.

-Yup.

I can see the umbra and the penumbra of some of those ones.

-The faint shadow around the sunspot?

-That's right.

And then Venus, of course, with no penumbra,

just the big black dot moving across the face of the sun.

Isn't that a fantastic sight? Venus is just so perfect.

-Lucie, you should get your solarscope out.

-It's bright enough now.

Finally we've got a shadow on here that I can use

to align it. Now...

There we go! Look, there's Venus

and one, two, three, four, five, six sunspots, maybe?

Fantastic!

And what I like about this Sunspotter is that

because the Earth is rotating so fast,

the sun is moving out of the field of view of my Sunspotter

so I'm always having to make an adjustment every few minutes.

It'd be much easier if the Earth didn't rotate!

-Working out the sun-Earth distance would be much easier.

-That's true!

So, here we can see Venus

looking pretty much like a very large sunspot

-with no penumbra, with no light around the edge.

-It looks darker than the sunspots.

-Maybe it's just larger.

-Yeah, much, much larger.

It's great to see it in such a simple... No offence to your Sunspotter,

but in such a simple device. That's full sunshine.

-Yeah.

-Let's look. Have you seen it with the naked eye yet?

-No, I haven't given that a go.

-Let's see if we can see this.

-OK.

Oh, yeah. There it is. I can see it.

That's rather nice.

-There's a band of cloud that looks rather pretty.

-It does.

It's about one-thirtieth of the width of the sun,

and I was worried that my eyes wouldn't be good enough to pick it out, but there it is.

All we need now is the rest of the clouds to go away.

'The sun is always changing

'and one type of feature that comes and goes is the sunspots.

'These can be bigger than the Earth

'and they're cool areas on the surface.

'Right now, there's a group of sunspots

'and also something called a "filament"

'where the sun's magnetic energy is holding up gas.'

I'm trying to see Venus with a hydrogen-alpha filter.

The sun is so bright that it makes it difficult to see

any detail on your computer screen.

But with my patented black shroud,

which got a lot of interest from some of the locals yesterday,

it helps me to see the detail. There's the sunspot group

and there is a giant, twisting filament,

a dark, snaking line, if you like,

running between all the sunspots there.

So that makes quite a pretty picture.

'I study the sun every day

'using spacecraft that look at it in different ways.

'Each wavelength tells you something different.'

One thing I wanted to ask you, Lucie. Pete's been imaging in hydrogen-alpha

so what exactly is that and what are we seeing in these H-alpha images?

In hydrogen-alpha, this is a narrow part of the visible spectrum

that the filter allows through,

and it's a really useful part of the spectrum to use

because it sees not the lowest part

of the sun's atmosphere - the photosphere.

That's the bit we normally see in most of the images?

Right. So when you see sunspots, it's normally the photosphere,

but the hydrogen-alpha sees a layer of the atmosphere slightly higher,

a layer that we call the chromosphere,

and this is the red layer that you see

-during a total eclipse.

-And what you pick up is the activity on the sun.

I noticed in one of Pete's images, as Venus moved across,

-you had what looked like squiggly lines just above it.

-Yeah.

-Are those the filaments?

-That's right. These are the filaments.

-They look like snakes on the surface of the sun.

-Yeah.

When you see them at the edge, we call them prominences.

-When they stick out?

-That's right.

But they're exactly the same thing.

They are relatively cool gas that's held up in the sun's atmosphere a little bit higher,

and I was really pleased to see

that there's a really nice S-shaped one

on the sun at the moment. There's a dispersed sunspot group

-that we were looking at in white light.

-I saw that.

When we moved up and looked in the hydrogen-alpha filter,

we saw not really the sunspots so much,

but we saw the filament that was also in that sunspot group.

So then we start to go up into the atmosphere, which is fairly hot.

It goes from 6,000 degrees centigrade at the surface,

up into millions in the atmosphere,

and you're right, that's what we start to see from space.

We start to look in ultraviolet light, extreme ultraviolet light,

and then even X-rays coming from the hot atmosphere.

Some of the satellites saw the transit before we did,

-cos they see Venus going through the sun's atmosphere.

-That's right.

Yeah, so now is a really nice era to have a transit of Venus,

because you're making use of the light

all across the electromagnetic spectrum.

There's going to be some fantastic images that come through.

It is magical, being here and seeing it the old-fashioned way

-and having the space-based images as well.

-Yeah.

'Colin has an ingenious arrangement

'with which to view Venus,

'and it's a safe way to look at the sun by projecting it.

'The transit's really a rather special sight,

'even at three in the morning.'

This is something I borrowed from a colleague

and it does look a bit like a pizza box.

It is a bit of folded cardboard. You get quite a good image.

Yeah, you've got the sunspots there, and Venus.

-It must be about mid-transit, I would say.

-Yeah. About mid-transit.

Maybe just past.

We didn't have this going for the beginning of the transit

because we've had clouds, but now it's glorious, in fact.

Yeah. It's good.

So actually, what I meant to ask you, while we're sitting here mid-transit,

is you are, of course, involved with Venus Express,

which is going around Venus. What's it doing right now, do you think?

Will it be making observations during the transit?

Yeah. It's got a 24-hour orbit, which is convenient,

so we know exactly where it is in its orbit.

At this time of day, in fact, around three in the morning,

is usually when it comes its closest to Venus.

It will be taking some particles and fields measurements,

so it's got its magnetometer recording magnetic fields.

It could be searching for lightning right now because we only

are sensitive to that when we're within the magnetosheath.

-When you're close in.

-Yeah.

-That's quite something.

The dot down there that I can see is a planet the size of Earth

and you're telling me there might well be storms.

-Suddenly makes it feel real.

-We've seen the signs of lightning.

-I don't think you'll see flashes.

-Not even if I look closely.

-No, no.

This transit is fun to watch,

but astronomers are using transits to study planets orbiting other stars.

Here we have an extraordinarily rare event.

We have a transit of an earth-like planet in front of a familiar star

and we can use all the transit analysis techniques on it.

And we can try to study it. We can look for signs of habitability.

And when we've done that analysis, we can see

whether we were right because we know what Venus is like in detail

because we've got a satellite there measuring it in great detail.

So if we find that our transit calculations are giving us

the right answers, that gives us a lot more confidence

in our analysis of exoplanets and our search for earth-like planets.

Venus is continuing its magnificent journey

and is now more than halfway across the sun.

Pete has been looking at it with a special telescope.

By using filters, he can look at different layers of the sun.

Seeing the calcium layer reveals hidden detail.

Pete, you've been observing with the calcium filter.

-Can I see some of your images?

-Yeah, sure.

I've sort of taken a whole sequence to try and get the entire disc on here,

but with calcium filters like this...

-This is the telescope that you were using.

-Yeah.

I sort of describe it like a super white light view.

It's like you get a view using a normal white light filter,

so you're looking at the surface of the sun,

but it's plus because you see all the bright regions

around the sunspots in the centre of the disc.

It's just full of detail, it's absolutely gorgeous.

I don't often look at the sun in this wavelength.

I'm familiar with visible light and familiar with the hydrogen-alpha.

Both of those I'd use in my research.

But I'm keen to see how it looks.

-We're looking at the chromosphere of the sun.

-Yes.

-Right at the bottom of it, is that right?

-Right.

So the emission can come from a variety of heights.

And the sunspots appear dark, still, so I can see those really clearly.

Yeah. But then you get this large granular network,

which is the chromospheric network.

That's right.

So what we're able to see is actually created by magnetic fields.

Where the magnetic fields are very strong, in the sunspots,

you have dark features,

which is the same as you have in the visible light.

But then this bright, mottled structure, that's still formed

by the presence of magnetic fields, but just weaker.

What's been your favourite wavelength?

Visible, calcium or hydrogen-alpha?

That's an awful question to ask! I don't know.

Once I've switched to one, I want to go back to another

because they all have their merits.

I think the white light looks fantastic.

But the calcium, you get all that beautiful detail underneath Venus

and moving across the disc.

And in H-alpha, you get all those beautiful snaking magnetic features.

-So my answer to your question is I don't know.

-All of them.

They're all lovely, yeah.

As well as the transit,

I've been enjoying my first experience of the midnight sun.

It's weird to think that we've been up all night and it never got dark.

Despite the fact, though, that the light hasn't changed, it is morning

and we're all beginning to feel a bit of nightshift strain,

but it's time to wake up because the end of the transit is approaching.

We're not far off the black drop here, actually.

This is Venus getting very close now.

This would be the point where you were struggling

if you were trying to measure the scale of the solar system.

This would be the point, wouldn't it, when you were just trying to time...

..things very precisely, yeah.

It's really wobbling around in the atmosphere.

-The atmosphere is very poor, yeah.

-Really, really poor, but we're...

-I think I can still see some...

-Gap.

-It's hard.

-There you go.

-That's it.

-There's the black drop.

-Yes!

So it looks like a connection between the blackness of space

and then, yeah...

And that's caused here

-because we've got such poor atmospheric conditions.

-Yeah.

That was third contact, so Venus is on its way off the disc of the sun

and there really can't be much transit left.

Right now we are in between the third and fourth contact.

And it's really amazing. Astonishing that we are seeing this.

We are lucky that the weather is now good for the final phase.

As we reach the end of the transit, with Venus just about to move off

the face of the sun, a reverential quietness has descended on Svalbard.

-A few minutes to go.

-Three minutes by my watch.

Yep.

-That's good enough.

-Yeah, then rotate across, that's nice.

You can just see it here. Just as we come up to fourth contact,

it's just visible with Venus on the edge of the sun's limb.

It's really going, isn't it? Even without the black drop, on this.

If this was what you were using to make your measurements,

say in the 17th century, has it gone?

Has it not? It's coming and going because of the atmosphere.

That's right, if you don't have really good conditions,

-this becomes even harder.

-That's right.

Goodbye, Venus.

Miguel and Michel cast their laptops aside

to see those final moments through the telescope,

just as their predecessors did centuries ago.

-It's gone.

-Yeah.

-Quick, record the time! Record the time!

-It's gone.

So we think that's it.

After hours of waiting for the skies to clear

and then hours of watching Venus move very, very slowly across the disc,

looking at the sun in different wavelength bands,

seeing the sunspots, the filaments,

it looks like Venus has finally gone from the face of the sun.

-It's rather depressing.

-I'm going to bed!

THEY LAUGH

You've been working hard, Pete, seriously.

Venus has departed, the show is over,

so let's see how everyone else got on.

Well, Colin? It's all done. How was it?

-It was good and bits of it were even sunny.

-Yeah, especially the end.

-Did you see third and fourth contact?

-Yes, yes.

Looking over various shoulders and trying to goad people

into telling me exactly when they occurred. It was great fun.

It's really difficult, isn't it, to judge that final...

No wonder their timings were difficult.

I found judging that third or fourth contact was really hard.

We had a couple of people looking through very similar equipment

and they disagreed by several... ten seconds, something like this?

Or more. Whereas meanwhile,

an observer on a different telescope was claiming 20 seconds out.

I heard you say, we were over there, and I heard you say,

"Has anyone seen fourth contact?"

-We thought it was 30 seconds earlier, so we were ahead of you.

-You see?

If we were a set of observers who had been sent out by the Royal Astronomy Society...

We'd be scrapping on the way home!

And we'd have done a great disservice to the whole astronomy community.

We'd have screwed up the universal measurements.

Thank God they don't rely on us any more. Not you and I.

Even though they've been up all night,

everyone is still basking in the glow of a successful transit.

We are happy that we could do it

because this morning it didn't look as if it would be possible.

-So I think it was worth coming here with all the equipment.

-Definitely. Definitely.

And I think we're quite happy.

It was very rewarding that the sun finally shone for us

at the end, after a long, long night.

With clouds passing. Yeah, it was fantastic.

The Venus Twilight Team, though, are still hard at work.

This is the edge of the sun, which is perfectly covered

by the cone, which is designed for that, actually.

It's off-centre, it's not in the optical axis of the telescope.

-This is what allows us to centre on Venus.

-Sure.

And so it's probably there, acquiring

and being written in the form of a file.

-This will be analysed later.

-Get the data first, do the work later.

-Absolutely.

The good news is that Thomas saw the aureole,

that beautiful, faint arc of light hanging in space.

Australia, too, got this lovely view,

although we still haven't heard from Ulan Bator and their elephant.

Pete also managed to get a glimpse of the aureole, an impressive sight.

On our Sky At Night Flickr site,

we have lots of lovely images of Venus as it went across the sun.

And they really show what a global experience this transit has been,

with images from as far afield as the South China Seas and Argentina,

and even some nice ones from the rather cloud-ridden UK.

Our spacecraft above the clouds also got some great images

and movies showing Venus flying across the sun.

This one, from the Solar Dynamic Observatory,

a very special event finished in the blink of an eye.

Well, the transit is over in a brilliant blue sky

and I'm feeling a little odd right now.

I've always known there'd be a transit of Venus in 2012,

and now it's over, and I'll never see another one.

That feels pretty strange.

On the other hand, we came somewhere spectacular,

with some remarkable people, and we saw an amazing sight.

That feels pretty special.

What a magnificent sight. And I do hope you saw the transit of Venus.

If not, look on the Sky At Night website.

When I come back next month,

we'll be talking about small amateur observatories.

Until then, good night.

Subtitles by Red Bee Media Ltd