Original subtitles

I can't even see the, like, the ground anymore.

It's just, like, we're just surrounded by blue.

I'm on an adventure to La Palma, in the Canary Islands,

with guest presenter Maggie Lieu.

We're at the Roque de los Muchachos,

one of the world's greatest observatories.

- That's just cool! Look at that! - Oh, this is so cool.

Doesn't it just look like a Hollywood sci-fi set?

It really does.

- Can we just stop? - Oh, don't worry, we're stopping just round here.

Look at this.

This is amazing.

- Not bad, eh? - It's so beautiful.

Now, from here, you could just take your pick of telescopes.

Places like this, to an astronomer, are magical.

Scattered on a handful of special mountaintops around the world,

they're our cathedrals dedicated to the sky.

And for decades, astronomers have been coming here

to ask the deep questions of the universe.

And the exciting new telescopes and clever new instruments

that we're here to see are getting us nearer than ever.

But on a clear night, if we're lucky,

there really aren't any better places on the face of the planet

for viewing the night sky.

- - Welcome to The Sky At Night.

I've been visiting places like this ever since I was a PhD student...

...and some things remain comfortingly the same.

No-one comes here for a luxury hotel,

but in these simple, pleasant rooms, there's a travelling circus

of astronomers from all over the world.

And they all want the same thing - a decent day's sleep

and clear skies at night.

The Roque de los Muchachos Observatory is a real wonder.

The multitude of telescopes here cover everything

from infrared to gamma-ray astronomy...

...allowing us to see further, faster and with more sensitivity

than ever before.

There's no time for me to settle in.

I want to see the new addition to the observatory,

an array of telescopes that was inaugurated only yesterday.

For astronomers using most of the telescopes up here,

the Earth's atmosphere is little more than a nuisance,

it just gets in our way.

But what if we could study some of the most extreme events

in the universe just by staring directly at that atmosphere?

An ambitious new project,

the Cherenkov Telescope Array Observatory, or CTAO,

is designed to do just that.

Dr Stuart McMuldroch is its director general.

Stuart, it's wonderful to be amongst these marvellous telescopes,

and they're brand new as well.

I hear you had your inauguration yesterday.

They are brand new, you know, and fabulous

to have the inauguration.

Tell me about them. What are they designed to do?

Everybody knows visible light, what we see with our eyes.

Well, we essentially image gamma rays.

So gamma rays are these very high energy...

They're very, very high energy. I mean, you go to the dentist,

you get your X-rays for your teeth -

imagine even more highly energetic than that,

about a billion times a light bulb.

Visible light reveals only a fraction of the universe.

Beyond what our eyes can see lies a hidden world.

At the extreme end of the spectrum lie gamma rays,

the most energetic light of all.

This is what the CTAO is built to study.

So, what sort of things might produce gamma rays

that you detect with these telescopes?

We're looking at the most extreme, highly energetic places

in the universe, which is cool.

We always talk about black holes, sure,

and we talk about AGNs, which are galaxies with black holes.

- Mm. - So we look at areas around these things which

accelerate particles at fantastic speeds.

Gamma rays are produced in the most violent of cosmic events,

like exploding stars and in the bizarre physics

that takes place around feeding black holes.

They streak right across the universe,

carrying information about their source,

until, that is, they hit the Earth's atmosphere,

But they can't get through the atmosphere?

No, they can't, so we use that fact, actually, to detect them.

- OK. - Because when they hit the atmosphere,

they cause a cascade of particles.

And those particles, in turn, create blue light,

very faint blue light that only, you know,

- last for, like, nanoseconds. - OK.

So that's why they have to be large, because that flash is faint.

But why do you need four of them?

- Because you're looking at different angles. - Ah, OK.

So, in order to work out where the thing has come from?

You can get the idea of where it came from,

down to a fraction of a degree.

So, in many ways, the telescopes are...

Well, the telescopes ARE working together.

Oh, very much so. Very much so.

They sort of talk to each other and say, "Well, did you see that?"

It's like, "I saw that. Did you see that?"

And because of that, we know that something is real.

So, what makes CTAO different from other observatories

that have come before?

Well, we have an order of magnitude increase in sensitivity.

- Just because you're bigger. - Yeah, bigger. Great cameras.

We cover a wider energy range.

This is a quantum leap to what we can do going forward,

and that's what makes this important.

Another aspect of this is that the telescopes can move quickly as well.

So tell me how fast and then tell me why that's important.

Well, I could ask you how fast you'd think these would move.

Well, they're big, right? So in my head, they're slow and stately.

- Exactly. - You know, Strauss playing and a slow move across the sky.

- Exactly, where you hear the waltz in the background. - Exactly so.

- Anywhere in the sky in 20 seconds. - Really?

- Something that size? - Yeah.

And the reason we do that is that there are particular things

called gamma ray bursts, GRBs, and...

HE CLICKS FINGERS ...they happen like that.

And so it's very important to try to capture that first gamma-ray flash

because, by looking at that gamma-ray flash, how it decays,

one can get information about what caused that.

Gamma-ray bursts unleash more energy in a matter of seconds

than our sun will generate over its ten-billion-year lifespan.

They're caused by dramatic events - collisions, for example,

of two ultra-dense objects - a neutron star or a black hole -

or by the catastrophic core collapse of a rapidly spinning stellar giant.

We're here at a really special moment.

People have been talking about CTAO for at least two decades,

and the observatory will be here for another 30 at least, I would think.

- That's right. - Let us know if you make a discovery.

We will, and thank you.

While Chris has been looking at the latest telescopes to arrive here,

I want to discover how a new instrument is revolutionising

one of astronomy's most useful tools -

spectroscopy.

By splitting light into its different colours,

we can gather information on distant objects in the universe.

For centuries, astronomers have been measuring these rainbows

one object at a time.

But what if a telescope could do it for hundreds of stars all at once?

That's exactly what Professor Gavin Dalton and his team are doing,

by adding an instrument called WEAVE to the William Herschel Telescope.

- This is incredible. - Thank you. Let's bring it down.

Wow.

- It's massive! - It's still cool after 100 times.

- It's so big. - It really is.

- So, this is your baby? - Yes.

So, this is WEAVE.

It's 1,000 optical fibres plus 1,000 optical fibres,

plus other bunches of optical fibres,

all of which we can place on the sky, looking at different targets.

We open the dome, we open the primary mirror covers,

the light comes through the dome, off the primary mirror,

back up through our correcting optics,

and brings each one to a focus on the fibre.

The light is then diverted down into our big spectrograph,

our detection machine, to analyse the spectra,

look at the chemical compositions, the velocities.

Anything you want to know about these objects,

you can extract from the spectra.

Once light is split into its constituent colours,

it reveals a wealth of information.

Embedded in the spectra are tiny lines,

the fingerprints of different elements.

By reading these cosmic barcodes, astronomers can uncover

what stars and galaxies are made of.

And when an object moves away

from us, its light is stretched,

shifting it towards red,

telling us about its motion.

Each optical fibre in WEAVE can look at a different target,

allowing it to collect this data for nearly 1,000 at a time.

The robots come in and then they position each one of those fibres

to within about eight microns.

And, essentially, they play chess.

- They play chess? - It's not predetermined. - OK.

So it's calculated on the fly because you don't know

how long each robot's actually going to take to move each fibre.

- Is it harder or easier than chess? - It's chess with a thousand pieces.

SHE LAUGHS

What does it take to engineer something like this?

It takes ten years, because you have a team of 100 people,

100 engineers working on it in six different countries.

There are 100km of optical fibre in the system.

- Wait, 100km? - 100km. - How do you assemble that?

So, it's all divided into 36-metre lengths,

which is here to the spectrograph, so we had to stretch them out

along one of our corridors in the department.

We were able to do this in the building

when the building was empty, so we had the corridor blocked off

for three days and nobody cared.

So, why do we need so many fibres?

So, one of our core science cases is to map stars across

the whole of the Milky Way, and in order to do that,

we really want to sample a few million stars.

If you do them one at a time, we'll be here long after

my children have retired.

So we tile the sky into two degrees at a time,

and within each one of those fields, we observe all of the stars

that we can sample, and that then takes us

about five years to cover the whole of the northern sky.

And if you have enough detail, you may be able

to see interesting things, like perturbations in the orbits

of different groups of stars, which might give you indications

of substructure in the dark matter of the Milky Way.

And that goes on to deep, philosophical

physics questions about how the galaxy exists,

what dark matter is, how it behaves.

Dark matter acts like an invisible, cosmic scaffold, shaping galaxies.

Without it, the universe as we know it simply wouldn't exist.

Despite outweighing ordinary matter by about six to one,

dark matter remains enigmatic.

We can only infer its existence by measuring gravitational effects.

So, the basic assumption is that the dark matter

is uniformly distributed, and if there's clumpiness

in that profile, that would tell us something

about how dark matter is composed, how the galaxy formed.

We're looking for clues to understand

what the nature of dark matter really is.

I've learnt so much here. Thank you for showing me WEAVE.

It's been a real pleasure.

As night falls on La Palma,

I want to take advantage of the amazing skies.

But what makes this location one of the best places

in the world for astronomy?

Well, the first thing is the height.

We're cutting through a quarter of the Earth's thick atmosphere

before a single photon even hits the mirrors.

The second thing is the air.

Over continents, heat rises over the land masses

and churns up the atmosphere.

But we're on an island surrounded by ocean,

and this acts as a temperature stabiliser.

And the last thing is darkness.

Here, the streetlamps shine straight downwards.

Blue light is minimised - hence why I'm in the red light here -

and after midnight, the whole island dims down.

I've brought along my smart telescope.

It's ideal for amateurs -

we can just point it at the sky, leave it running

and just go back into the warmth.

And it didn't take long to get some images that I wanted to share.

- Chris. - Hey, Maggie. How's it looking outside?

- It's amazing. Look at all the images I've got. - Already? - Yes!

This is Triangulum.

That's spectacular.

So, you can see all the spiral arms.

That row of stars is interesting, that's kind of cool.

I don't think I've ever noticed that before.

So these are just with the small camera from outside?

Yeah, it's from the smart telescope.

- Orion Nebula. - It's my favourite.

- Gorgeous shot. - It's so pretty. - Look at that. Look at the detail in this.

You've even got... Is that the Trapezium in the middle there?

What do you make of the sky from out there?

Oh, it's so clear. Like you said, there's so many stars,

- I can't figure out where my constellations are any more. - Right.

- Shall we go out and do some more? - Yeah, let's get out there.

While we're enjoying the skies on La Palma,

back in the UK, Maggie Aderin is discovering

how data from the observatory's GOTO telescopes

is being shared with the public,

helping tackle one of the universe's greatest mysteries.

It was Carl Sagan who famously said,

"We are all made of star stuff."

And it's true - the carbon in our bodies,

the oxygen in the air,

the phosphorus that makes the backbone of our DNA

was all forged in the heart of dying stars.

But it's not that simple. Stars like our own

are only capable of producing elements as heavy as iron.

At the University of Warwick,

a citizen science initiative co-led by Dr Lisa Kelsey

is hunting for the cosmic source of heavier elements,

everything from the gold in your wedding ring

to the uranium in our power stations.

- Lisa, lovely to meet you. - Thank you.

Now, can you tell me more about your project?

Kilonova Seekers is really designed

to bring members of the public into transient astronomy,

- and it's quite simple as a game of spot the difference. - OK.

So, every roughly 15 minutes, data is sent onto our platform,

and really, what we want the public to do is see,

is there something in that image

that either the computer algorithm has just missed,

or is there something that we should be finding as quickly as possible?

So, you mentioned a transient event, tell me more about that.

Yeah, so that is when something has changed in the sky.

So that can be an asteroid has suddenly appeared on the sky

or it could be something like a star going supernova.

Transient astronomy studies fleeting phenomena

including exploding stars,

gamma-ray bursts and kilonovae.

Now, what's the source of your data?

Our data comes from the GOTO telescopes -

that is the Gravitational-wave Optical Transient Observer.

These telescopes were originally designed

to follow up gravitational-wave triggers.

When it's not doing that,

it just operates like a normal, all-sky survey telescope.

Fully robotic, the GOTO telescopes on La Palma

constantly scan the skies for astronomical transients,

but they can also react within a matter of minutes

to gravitational-wave alerts

from an international network of detectors.

- Now, your Kilonova Seekers... - Yes.

...we need to break down. What is a kilonova?

So, a kilonova is when you have two neutron stars

that are orbiting around each other in a binary system,

until eventually they collide quite dramatically

and make this luminous explosion.

And what they do is they create

a lot of the heavy elements in the universe.

Neutron stars are the cause of dead stellar giants.

Second only to black holes in their density,

they can pack more mass than our sun

in a sphere that is just 10km wide.

When two neutron stars collide,

the forces are so extreme that heavy elements can be forged.

So the gold, silver and platinum found here on Earth

probably have their origins in an ancient kilonova.

- So, you're hoping to spot a kilonova. - Yes.

But when you see it, what will it tell us and how?

What we're really trying to understand is

where the heavy elements in the universe are actually coming from.

So, to detect this, we need to look at the spectral signatures

that we're actually getting from the kilonova.

So, as we see that evolve, it will tell us more

about how these elements are forming and changing in the universe.

But to date, we've actually only really found one

confirmed, solid kilonova, which is a little bit of a problem.

In 2017, telescopes around the world

observed AT 2017gfo,

the first and only definitive kilonova.

- How many volunteers do you have? - So, at the moment, we have

about 5,000 volunteers, really from all over the world.

They're doing it on the bus on the way to and from work.

You always need a human looking at the data,

because the computers are quite good at finding out what is real,

but humans are even better at detecting patterns.

And with the amount of data that we have that is coming

and streaming through, scientists in the GOTO collaboration,

we have to prioritise what it is that we actually look up

- and observe ourselves. - I think the million-dollar question is,

when do you think you'll find your first kilonova?

I'm putting you on the spot here!

So, we're really quite hopeful, actually.

So, LIGO and the other gravitational-wave instruments

are starting a new run. So I'd like to say in the next year,

but we'll see where we are a couple months down the line, I think.

- So, effectively, watch that space. - Yes, yeah.

Back in La Palma, before we leave the mountain,

there's one more thing I want to see.

This magnificent beast is the Gran Telescopio Canarias,

the largest of its kind anywhere in the world.

This huge mirror collects large amounts of light from the night sky

and I'm here to see what a remarkable new camera,

which concentrates on the fastest-changing objects

in the universe, is doing with it.

Professor Vik Dhillon is leading the HiPERCAM project.

- Vik, how nice to see you. - Hello. Welcome to the GTC.

- It's an amazing place, isn't it? - Fantastic, yes. - Wonderful.

- Where's your bit? - Up there, on the platform.

- So we have to go up in this amazing lift. - OK.

- How high are we going? - About ten metres.

- OK. - But it's quite fast.

I'm glad you said that.

Oh, yeah, you're right, that is quite fast.

Yeah, that's much faster than I was expecting.

OK, so, if you come this way.

- It's spectacular. It's got... - Yeah. - I don't know, it's got bits.

This is HiPERCAM. So, the light comes from the sky,

reflects off the 10.4m-diameter mirror,

- the largest in the world. - All the way down there. - Yep.

And then bounces back up to the secondary mirror,

which you can see up there, at the top of the tube.

And then there's a tertiary mirror, which is behind this metal wall,

which sends the light into HiPERCAM.

So all that collecting power of the telescope

is brought to HiPERCAM, where it can then take images.

That's what people don't realise, I think - the telescope's just

- a light bucket. - Exactly. - But all the interesting stuff

happens with the instruments here.

So what is it that's special about HiPERCAM?

I guess it's got three really unique properties.

It's a high-speed camera,

- so it can take 1,000 images a second. - 1,000? - Yes.

- That's extraordinary. - Yes.

So that's compared to a typical camera at the observatory here,

which typically does one exposure every minute.

It takes the white light that's coming from the telescope

and splits it up into its component optical colours.

So you simultaneously record five images,

each in a different wavelength of optical light.

Well, the third thing is that we're here,

we're permanently mounted on the GTC,

which is the world's largest optical telescope, which means it makes

this the world's most sensitive optical camera as a result.

What sort of things have you done with it?

I think the most exciting things

are looking at the most rapid variability in the universe.

And the things that change fast in the universe tend to be

the small things, like white dwarfs, neutron stars and black holes -

these are objects which are Earth-sized or city-sized or below,

and they can vary on timescales of down to a millisecond.

- I hear you've been looking at solar system objects as well. - Yes.

Surely nothing in the solar system changes on time scales

- of milliseconds? - Yes. Amazingly, they do.

Particularly through an effect called occultations.

So this is where you've got a small solar system object,

- like a dwarf planet... - Something in the outer solar system. - Yes.

And every now and then, it'll obscure a background star

- many, many light years in the distance. - OK.

- And so that must give you the size of the dwarf planet. - Exactly.

Because we know how fast the dwarf planet's moving

and we know how long it takes to cross the star.

We saw the main event when the planet passed in front

of the background star, but just before and just after,

- there was another little dip, and that was a ring system. - Oh.

So we discovered a new ring system,

the seventh known in the solar system.

This was called Quaoar. This is one of these dwarf planets.

And every ring system known to date

has been within what's called the Roche limit,

until the one we found, which was two to three times outside it.

So it really stumped theorists.

The Roche limit is a theoretical line,

within which any asteroid or moon

will likely be ripped apart

by the planet's gravity.

That's how we get spectacular rings

like those around Saturn.

But Quaoar's rings are further out,

so we don't know how they formed.

I love that you've accidentally found something that's meant

the theorists have had to rewrite... But have I heard right?

- You found other rings as well? - Yes. So we did on another one of these

dwarf planets, out there beyond Pluto, called Haumea.

Haumea -

a tiny, barren, egg-shaped world -

lives amongst the Kuiper Belt,

an icy collection of rocky bodies and dwarf planets

in the far reaches of the solar system.

That ring system was known, but it was barely detected

in its original discovery.

And we did it with this back in May, and it's unpublished, that data.

And it blew our minds because not only did we see

two little dips when the ring passed across the star,

the dip had a W shape in it.

So, essentially, it looks like the ring has got some structure.

- There's like a Cassini Division... - Like in Saturn's rings?

Like in Saturn, which then tells you

there must be some kind of shepherding moon or moonlet...

- Oh, to create the ring. - To create the gap, yeah.

- So that was quite exciting. - I think you're clearly having great fun.

How much does it matter to you

that you're an astronomer who gets to use it,

and you're somebody who built it and helped build it?

I think the most successful instruments

are the ones where the team who built it

- are the ones who actually also want to exploit it scientifically. - Yeah.

And that's certainly the case for the team that built HiPERCAM.

Pretty much every time we turn it to a star, we find something new,

so that's a really important motivator.

Well, Vik, it's a fabulous thing and the results are astonishing.

I wish you many more clear nights.

- Thank you. - And maybe I'll come and use it one day. - Oh, you'd be

- very welcome. - Thank you very much. - Thank you. - See you soon. - Thank you.

You don't need HiPERCAM to enjoy the night sky.

As the year draws to its end, Pete has plenty for us to look up at.

If you set your alarm for the early hours of the morning,

there's something of a treat in store for you.

That's as long as the clouds stay out of the way, of course.

Mars and Jupiter are performing

a solar system dance

against the backdrop of Leo and Cancer.

Regulus, the brightest star in Leo,

acts as an anchor against which the planets appear to move.

And the moon looks really impressive too.

On the 28th of November, it passes across

the beautiful Beehive Cluster, at the heart of Cancer.

Every December, the constellation of Gemini

becomes the stage for one of the year's most spectacular shows -

the Geminid meteor shower.

At their peak,

perspective makes meteors

seem to burst from a single point,

known as the radiant,

which lies near Castor,

one of Gemini's famous twin stars.

Its celestial sibling, Pollux,

shines close by

as the sky comes alive

with shooting stars.

Best viewed after midnight,

the Geminids are arguably

the most impressive meteor shower

of the year,

with a maximum zenithal hourly rate

of around 150 meteors per hour.

This makes them great photographic targets,

and this year, the moon sets early on too,

leaving the whole night perfect for meteor watching.

Just remember to wrap up warm.

If you get any photos of the Geminids

or anything else in the night sky,

do share them with us on our Flickr page,

details of which can be found at...

The revolutionary new tools and cutting-edge science on display

at the Roque de los Muchachos Observatory are extraordinary.

And as the sun sets over the Atlantic far below,

there's nowhere I'd rather be.

So, as we sign off from this year's series,

I'll leave Chris to savour the remarkable beauty of this place.

These domes scattered across the mountainside

are opening to the sky one by one,

and assuming the night stays still and clear,

a small miracle of science is about to happen.

The precious light they gather tonight will be treasured,

shared, explained, processed and analysed

over weeks and months and years to come,

until the astronomers that came to the mountain to grab it

have the answers to the big questions that led them here.

I find it inspiring, but this time of night also reminds me that,

in modern astrophysics, with all its complicated telescopes,

instruments and cameras,

we're only doing what you can do on any clear night at home.

Go outside, look up, wonder about the universe,

and share with us the ever-intriguing sky at night.

Goodnight.