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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.