Original subtitles

To understand how we humans have connected to the night sky

throughout history and across cultures

has always been close to my heart.

It shows of a shared understanding of the universe

that goes back through generations.

Before this modern age of giant telescopes and space missions,

humans still marvelled at the vast cosmos we inhabit,

looking up as the stars and planets,

the moon and the Milky Way turned above their heads.

But to understand how the early humans made the connection,

we need to look to archaeology to tell us more.

And it turns out it has a lot to tell us.

So tonight, we're looking at the unexpected places where

astronomy and archaeology intersect.

BOTH: Welcome to The Sky at Night.

When I was growing up, I always thought that all astronomy

was done by white guys in togas.

That's what I heard! THEY LAUGH

Certainly the impression I got - that it was some clever,

bearded Greeks doing maths, mostly with triangles,

that laid astronomy's foundation.

But since then, I've discovered a whole wealth of information

and found out that every culture has looked up and been amazed

by the night sky. Absolutely.

So tonight, we're looking at ancient, modern

and future interpretations of that night sky.

And to do that, we have teamed up with our colleagues from BBC Ideas

to help us on our way.

For most of human history,

understanding the sky was not the preserve of scientists,

but a precious tool for our survival,

for building cultures, religions and societies.

And in some places, it still is.

This is Orion the Hunter.

You're probably familiar with his belt and sword.

But if you're close to the equator,

it looks a lot more like a canoe.

1,000 years ago, the Polynesians were the most

accomplished navigators in the world.

Up to the 11th century, they explored over 1,000 tiny islands

scattered across the Pacific Ocean.

One of the ways they did this was

by using an ingenious memory technique.

With a stone canoe built on the beach,

a trainee navigator would face the sea and sit in there

night after night,

memorising the rising and falling positions of the stars.

When the crew was ready to depart,

they would head for a star near the horizon,

switching to a new one once the first either rose or set

as it moved across the sky.

Each sailing route required a specific sequence of stars,

like a password or a musical motif.

Observations of the sun, moon, and stars were just as important

for ancient people on land.

They used them to mark the turning of the seasons,

specific events like solstices

and even the location of sacred sites.

Remarkable archaeological evidence for this can be found in places

from Malta to Mexico

and from Egypt to Cornwall,

a little closer to home.

George has set off to a site in the Cornish Moors to find out

more about our Celtic ancestors' relationship with the sky.

The UK is sprinkled with prehistoric monuments,

these mysterious stone structures that are well over 2,000 years old.

Now, that's long before our ancestors started leaving

behind written records - so sadly, the exact purpose

and meaning of these sites has been lost to time.

Archaeologists have been working on them for decades,

trying to dig up the past.

But there's a relatively new crop of researchers that are helping

to decode these sites in a different way -

by looking up at the skies above them and seeing if there's

any links to the stones below.

I'm at Bodmin Moor to meet Carolyn Kennett,

an archaeoastronomer.

She's trying to piece together the history of Goodaver Stone Circle -

a site that will soon be open to the public.

So, Carolyn, aside from being the world's coolest job title,

what exactly is an archaeoastronomer?

An archaeoastronomer investigates sites like this

and considers how they connect to the sky above.

It's really interesting because,

not only looking at the sky and the movements in the sky,

we're also considering the cultural

connections that the people that built the site

would have had to the night sky.

How old is this stone circle specifically?

So, Goodaver is a typical Bronze Age stone circle.

We're on Bodmin Moor, and the stone circles here probably date

to around 3,500 years ago.

Although this circle hasn't been carbon dated,

it shares many similarities with

other local Bronze Age sites that have.

But there is something that sets this stone circle apart.

So, this site is quite unique on Bodmin Moor.

Many of the sites are down in bowls in the landscape,

with big hills around them,

whereas we're on quite a ridgeway here.

And it seems to be a mid position, where people were perhaps

coming to gather to meet here specifically to look at the sky.

For the past century, this site has been hidden by trees.

With the obstruction gone,

Carolyn can now work out if the position of the stones

had any relevance to the ancient sky above.

We have access to wonderful digital and 360 photography nowadays,

and planetarium software allows us to rewind and fast forward the sky

across a number of different dates,

including the time when we think this stone circle

would've been in position.

First, Carolyn is taking overlapping images of the stones -

the basis of her 360-degree digital horizon.

These are all beautiful shots, as well.

VOICE-OVER: Now we've got the exact position of the stones,

it's time for the software to fill in the sky.

SHUTTER CLICKS

So, we know that the sky is always changing -

but what changes are you actually looking for?

There are two changes.

There's something called precession,

which is a 26,000-year change

to the position of the north celestial pole. Mm-hm.

So, we see Polaris in that position right now.

If you rewind into the Bronze Age,

there would've been a different star there.

The other change is a longer cycle,

which is called the obliquity of the ecliptic.

And it's to do with the tilt of the Earth,

and it's a 41,000-year cycle.

And that means, in the Bronze Age,

that the sun rises and sets further south in the winter solstice,

and further north in the summer solstice.

There's a significant change! It is, yeah. Yeah!

Can we actually see on here what it looked like then?

So, we can actually rewind this back in time.

There you are. Yeah! You're starting to set over in that direction.

Yeah!

That's fantastic.

What has your research actually shown so far, then?

We've been able to show the alignments with the Equinox

are pretty bang-on, but we've also found that,

if you were to approach from a line of barrows,

you're actually going to see the moon at this position.

And that's something that we've been able to replicate

on the planetarium software.

These alignments suggest just how important the movements of

the sun and moon would have been to the people that lived here

thousands of years ago.

And this is just the start of Carolyn's research.

I have to say, this has been a truly fascinating outing for me

and I'm so grateful to you for inviting me

to my very first stone circle.

Oh, I'm really pleased you've enjoyed it. Yeah!

The Goodaver Stone Circle is just one of thousands of stone monuments

across the world, and a relatively small one

in the grand Stonehenge-y scheme of things.

MAGGIE: Stonehenge is solstitially aligned -

meaning if you're approaching the entrance from the north-east,

the sunset at midwinter will cut the monument neatly in half.

Newgrange, in Ireland, does an even better job.

A 19m passage runs the length of a long barrow,

leading to a central chamber.

In the mornings around the winter solstice,

the sun shines directly in through a crack above the doorway.

Newgrange was a tomb, so for the people that built it,

ancestors, death, the sun and seasonal renewal

were probably linked.

Perhaps it was the job of the ancestors to turn the sun

around at midwinter,

guaranteeing the return of spring.

One of the most stunning examples of an ancient astronomical tool

is at Chankillo, in Peru.

A line of 13 towers provided a detailed solar calendar

to someone viewing it from a specially-built doorway.

Archaeology helps us understand the significance of these sites

to ancient civilisations.

But the principles that it uses are also giving us insight

into a very surprising area -

the evolution of galaxies.

Chris is headed to the University of Cambridge's

Department of Archaeology

to find out how astronomers are learning from the best in

the archaeological business.

CHRIS: Just like archaeologists, astronomers are stuck with

whatever the universe gives us.

An archaeologist can't ask for a different bit of Roman villa

to be preserved,

and I can't reach out and flip a galaxy over to see its far side.

We get whatever we get.

We just have to do our best to tell true stories

about the past from it.

I'm meeting anthropologist Professor Robert Foley

and galactic archaeologist Dr Payel Das...

..in a roomful of casts of skulls, of course.

Payel, you're a galactic archaeologist.

What does that mean?

So, we're using archaeology here very much in the metaphorical sense,

because we're obviously not looking at the history of humans.

We're really trying to understand how our Milky Way evolved

using stars that we can observe - we call them stellar fossils,

a bit like the fossils on Earth.

And, even though we observe these stars now,

they were actually born at different times in the Milky Way's past.

So, if we can measure how fast they're moving or where they are

in the sky and what they're made out of,

we can sort of piece together the history of our Milky Way.

So, Rob, you're an anthropologist, somebody who's dealt

with archaeology for a lot of your career.

What do you think about this term - galactic archaeology?

ROB CHUCKLES

Well, a bit of a surprise, really, to start with,

but I think what we share with the galactic archaeologists is we're all

trying to reconstruct a history

we can't observe directly.

We can't go out and actually create the conditions under which

stars evolve, or which human societies, you know, develop.

Galactic archaeology has been revolutionised by ESA's

map-making satellite Gaia.

It's revealed a surprisingly complicated history of

the Milky Way, full of violent mergers with other galaxies.

But making sense of Gaia's observations of billions of stars

needs creative thinking.

Rob, how did you get mixed up in this world?

THEY LAUGH I-I guess by accident.

I was actually giving a talk on how evolutionary biologists use trees,

because everyone's familiar with the idea of an evolutionary tree.

You know, you can find one in Darwin's Origin of Species.

And of course it makes sense

because, from common ancestors,

organisms diverge as they evolve.

And I gave this talk and, erm, Paola Jofre,

who was the sort of first person who really got this all going,

came up to me afterwards and said, "Can we try this with stars?"

And, erm, I have to say, my first answer was, "No."

THEY LAUGH

For the reason that you've got to have some mechanism by which stuff -

in our case, of course, it's DNA -

is transmitted from one generation to another.

So, how do stars actually develop

and is there a process of heritability?

And, indeed, there is.

What is it that stars are inheriting?

All stars are born from gas,

and we call this gas the interstellar medium,

the gas that exists between stars.

And so, from that, you have the birth of these stars.

And then, over time, when the most massive stars die,

they basically eject all this material,

and that's put back into this gas reservoir.

And then, the next generation of stars is going to be born

from this new gas.

Chemical elements are transmitted from one generation to the next,

as stars die and form from these clouds of gas.

But would this inheritance really be enough to make

an evolutionary tree for stars work?

So, our first paper, back in 2017,

we chose a very small sample of stars for which we really trusted

the chemical abundances.

So, I think it was 22 stars?

And we applied these techniques.

We were sort of reaching out in the dark here,

and then we just couldn't believe what we saw.

The first tree we made, I was like,

"That's a bit like the Thick Disc,

"that's a bit like the Thin Disc, so these are..."

Different bits of the galaxy? Exactly.

And there was a group of stars there we didn't really understand

as well, that came out as possibly ancestral to these disc components.

That's a remarkable result -

finding not just known parts of our galaxy on different branches

but, deeper within the tree, a group of fossil stars,

the ancestors to the others.

More detailed trees with more stars later confirmed the existence

of this ancestral group.

And that small team from 2017 has now grown into an international

collaboration of astrophysicists and anthropologists,

biologists and mathematicians.

I realised that I think astronomers had been doing it all wrong,

essentially - we're always trying to work out how different stars are.

But I think what's been really refreshing about talking with Rob,

and evolutionary biologists in general, is they're trying to

work out how connected stars are, not how separate they are.

You know, we were very ignorant to each other's fields,

and you can only start to work together if you're prepared

to express that ignorance.

And obviously, "I really don't know, I don't understand."

And that requires trust and friendship to be able

to build the shared knowledge.

It's always fun when you spend time with two scientists having

that much fun working together,

especially when they come from such different backgrounds.

But I think their collaboration's still deep in

the roots of their tree.

And I'm looking forward to seeing what branches develop.

MAGGIE: Exciting results like this come from looking out

into space and asking - why?

Something we've done for centuries as we ponder the stars above us.

But in the modern world,

our relationship with the night sky is changing.

With the development of complex technologies, such as GPS,

most humans no longer rely on the sun, moon

and stars to travel, or to organise their lives.

Just as well, because light pollution is increasing globally

between 2-10% year on year.

Only one in five people in Western Europe and America

can now see the Milky Way.

But birds need the stars,

including the North Star, to navigate.

If they can't see them due to light pollution from cities,

they run into trouble.

Denying animals access to the stars is just one of the many ways

in which light pollution impacts nature.

Anyone that likes to look up at the stars will know the problem

of trying to find a spot to get the clearest view.

Excess light from towns and cities up to 120 miles away

can still spill over into the night sky, hiding the stars.

But there are places all around the world where people

are working hard to preserve that nocturnal view.

Back in 2011, Exmoor National Park was awarded

International Dark Sky reserve status.

Over the years, a lot of work has gone into ensuring the area's lights

are kept to an absolute minimum,

and that allows incredibly clear views of the stars up in the sky.

That's when the weather allows it, of course.

To find out why places like this are so important,

I'm meeting Jo Richardson.

If somebody asked you,

how would you explain the importance of a dark sky reserve?

I think they've become more important as time has progressed.

And I think, in an ever-changing world with more population,

more development, I think it's really important that we have

these sacred spaces where we can escape to and experience

truly dark skies, not just for stargazing,

but obviously, to protect the ecology as well. Yeah.

There's actually been a lot of research to do with human health,

because we know that light-polluted skies has an effect on the human

body and circadian rhythms.

Recent research is finding light pollution not only disrupts

our sleeping patterns,

but could also be linked with a risk of diabetes, strokes

and even cancer.

And it's not just us humans that it's harming.

Research has shown with lots of animals,

certainly nocturnal animals, their behaviour, breeding,

feeding patterns are all changing.

And even things such as insects -

we've got evidence of insects coming out at night when...

Right, wow. ..you know, they're meant to be out in the day.

So, it's certainly very important.

And it's very important here on Exmoor National Park because,

as we say, it's not just about stargazing,

we also have to look after the ecology of the park as well.

So, for people at home,

is there anything they can do to improve the situation?

We often say, it's not about turning all the lights off.

We don't expect everybody to live in the dark. No.

What we do expect, perhaps, is for people to be more aware of it

and use the right type of lighting in the right circumstances,

and obviously only when it's needed.

Things like, for example, using red light if possible.

It's not as bad for your night-vision

as is bright white light.

Pointing lights downward.

Pointing up into the sky is pointless.

THEY CHUCKLE You need to aim your light...

That's a good slogan - could use that one.

You need to aim the light exactly where it's needed... Yeah.

..as opposed to just allowing it to spill over.

It's work like this that's done across the whole of

the Exmoor Dark Skies site

that allows for stunning views like these.

We're hoping to go out later tonight to do a night walk.

Weather looks a little bit iffy.

Yes, it does.

And it's not that great at the moment.

It's actually quite frustrating.

However, we often have plan B. Right.

And plan B is that we will stay in the warmth of the tea rooms,

and we'll have a look at the night sky in a virtual way instead.

So, it's still a lovely evening. Oh, well, that's exciting.

I've got my fingers crossed that the weather improves for us tonight.

Thank you very much for your time, and I'll see you later. Thank you.

If this was the size of the sun...

Oh, look, she's even acting it! It's fantastic!

Though the weather didn't improve,

plan B was fun.

But with so much to see in the coming months,

I'm keeping my fingers crossed for clear skies.

You don't need fancy equipment to enjoy the night sky.

Your eyes will do just as well.

And there's plenty of bright things to look out for,

including the planet Venus.

But you will have to wait until towards the end of the year

for an easy view of the planet.

Luckily, on the 4th and 5th of December,

the waxing crescent moon will make locating Venus very easy.

Wait until the sky has darkened after sunset from around 5pm,

locate the moon, which will be low and near the southern horizon.

Then look for the bright light of Venus -

perfect for spotting with the naked eye.

So, if you're an absolute beginner,

this is an easy one to start with.

Another planet in a great position is Jupiter,

which is currently prominently bright, beautifully presented

against the exquisite stars of Taurus.

Again, the moon can be used as

a locator for this planet.

And on the nights of the 16th and 17th of November,

the bright gibbous moon sits near Jupiter.

For the more advanced stargazers,

as it approaches opposition,

there is great potential to see some amazing moon

and moon shadow transits.

On the night of the 8th of December,

don't miss the giant moon Ganymede -

that's the largest moon in the solar system -

crossing Jupiter's disk,

virtually touching its shadow as it goes.

The event starts around 10:30 on the night of the 8th of December,

and concludes around 0050 on the morning of the 9th of December.

You can also see Io in sync with its shadow

from 0356 until 0608 on the morning of the 9th of December.

And moving closer to home, we've got the planet Mars,

which is looking pretty good as we head towards the end of the year.

And there's an interesting project you can do,

which involves tracking the planet against the background stars.

Mars heads towards the Beehive cluster M44

in Cancer the Crab during November.

However, as it moves to a position just to the north-west

of the cluster stars, its apparent

direction in the sky reverses.

Before the 6th of December, Mars moves in a prograde -

or west-to-east fashion.

After this date, it's moving in a retrograde manner -

east-to-west.

This will continue until the 24th of February,

when the planet once again reverses its direction

to head east once more.

Eventually, it will catch up with the Beehive,

appearing to pass across the cluster in May of 2025.

This odd motion is caused by the difference in orbital speeds

between the Earth and Mars.

And don't forget, there's also the Mars Occultation in December

that I detailed in the last episode.

As ever, if you take any photos,

do share them on our Flickr page.

We'd love to see what you've captured of the sky above you.

Here are a few which we've received recently.

CHRIS: Humanity's relationship with that beautiful night sky

forms a huge part of our heritage.

So, how do we preserve it for generations to come?

Back in Cambridge, Maggie's at the Whipple Museum,

home to incredible objects like this magnificent orrery from 1750,

used to model the intricate motions of our solar system.

MAGGIE: We keep objects like this in museums because

they're important to our history.

And it's not too much of a stretch of the imagination

to realise that many of the artefacts that we've put into space

also have a cultural significance.

Telstar 1, the world's first active communication satellite,

is still up there in orbit.

While it is now technically defunct,

it is an important part of our history.

Without it, we might not be able to communicate in the ways

we are used to today.

Because of the success of satellites like Telstar,

I'm now able to speak to friends and family in an instant -

but also speak to experts in Australia, for instance.

Hello, Alice, can you hear me?

Hello, Maggie!

Associate Professor Alice Gorman is an archaeologist,

heritage expert and an internationally-recognised leader

in the exciting new field of space archaeology.

I believe you can be called Dr Space Junk.

Why did you acquire this title?

THEY CHUCKLE

The very first time I started to think about space archaeology

was when I was just looking up at the stars.

Ah. I had a revelation, and I suddenly thought to myself,

"There's space junk up there,

"and it's an archaeological record."

And that was it. Like, I was hooked.

My entire career changed from that moment. Wow!

Space junk and satellites present a particular conundrum

for archaeologists like Alice.

While defunct satellites crowd our orbit and satellite

megaconstellations create light pollution and alter the night sky,

there are some satellites that have cultural significance.

We say that all of the stuff in Earth orbit that's not

an operating satellite is junk,

and that's not strictly true.

I'm interested in spacecraft which have historic or scientific,

or social, spiritual significance.

We know we've got to get rid of some space junk.

We know it's a big problem.

But you have to be able to discriminate between

what has value and what doesn't.

Well, think of, you know, Palaeolithic archaeology hundreds

of thousands of years in the past.

If somebody at that point had stopped to think,

"Well, what might people in the future like to have more of,"

and started preserving that,

we'd be in a very different situation right now.

There are hundreds of sites and objects on the moon that hold huge

cultural significance for humanity,

and preserving them becomes more and more challenging

as we continue our exploration of the lunar surface.

There's a common idea that

the bootprints on the moon,

for example, will stay safe,

untouched for millions of years.

So that we don't have an atmosphere,

we don't have microbes, jungles, watercourses -

all of these things that degrade human materials.

But it's still actually a really active place.

It's constantly bombarded by tiny micrometeorites,

sometimes larger ones as well,

and now we're adding human rockets to the things that bombard

the surface of the moon.

The bootprints of the Apollo 11 astronauts already hold

so much meaning for humanity,

but their cultural significance actually goes beyond

what most of us know about their story.

There is a really important factor in all of those Apollo sites

where women have played a big role, too.

So, the Apollo spacesuits,

they had to get expert seamstresses,

and these are the women that made the spacesuits

that kept the men alive.

And when they stepped out of the spacecraft,

those famous missed bootprints are actually made by overshoes

that they had to pull on.

These overshoes were discarded on the moon.

They're part of the artefacts left behind on the surface.

But they were made by women.

So, we could look at

these bootprints as

they were made by the foot of a man,

but the hand of a woman.

It still feels a bit weird to be talking about

the archaeology of space,

because the space era is so young.

And yet, I think it makes sense to ask the right questions now.

Work out what we want to preserve, in terms of our space heritage,

for generations to come, in maybe thousands of years' time.

So, that's it for this episode - and indeed, this series.

But we will be back in the new year.

Until then, you can find all of this year's episodes on the BBC iPlayer.

If you want to see the full version of the animation

that we showed you earlier,

it and many others can be found on BBC Ideas.

In the meantime, do get outside and do keep looking up,

because it's important for all of us.

So, until next time...

BOTH: ..goodnight.