To us, the night sky is a fascinating spectacle.
To our ancestors, it was the key to their survival.
They had to understand these patterns
in order to do the planning they needed to survive as a culture.
lt was this relationship with the heavens
that led to some of mankind's greatest discoveries and creations.
We built our largest monuments - things like stonehenge, the Pyramids.
They're aligned to the stars, they're related to them.
These masterpieces were created with such perfection
that some believe the ancients had divine help from above.
Our ancestors built the Pyramids with the assistance of the guardians of the sky,
otherwise referred to as the gods.
Over thousands of years,
there have been many scientific discoveries, but it was these first observations of the cosmos
that put us on the path to modern civilisation.
ln this programme, we're going to see why looking up all those thousands of years ago
sowed the seeds for civilisation.
We'll start in the distant past to see how the skies gave us our first clocks and calendars.
We'll see how this predictability of time gave the ancients a chance to focus less on survival
and more on cultivating society.
The skies began to take on religious significance
and the stars were used to explore new worlds.
scientists are still using some of those navigational techniques today to explore space.
And finally, we'll delve into the deep mysteries
that still surround our ancestors' worship of the skies,
like theories of ancient astronauts visiting our planet.
We're about to unravel how the ancients decoded the skies.
Today, if we want to know the time, we look at a watch.
For the date we look at a calendar.
We know it's autumn because of a new TV schedule.
some might know it's spring because certain sports seasons are beginning.
The skies don't mean that much to us any more.
lt's kind of ironic that today we don't have to pay much attention to astronomy in our daily lives.
We don't have to worry about exactly how many days are in the calendar and all that
because we've figured that out.
And we figured that out because the Mayans figured it out.
The Egyptians, the Greeks, the Romans figured that kind of stuff out.
so our daily lives depend on what these ancient civilisations did.
lt's a good thing our ancestors studied the skies
because nowadays, some of us don't even look up any more.
That was made clear in the hours after the Northridge earthquake in 1 994.
The earthquake had knocked out all the lights of Los Angeles.
lt was dark like it's never been in southern California.
We started getting calls from people who wanted to know
what was that peculiar odd sky that they saw.
People were phoning the Griffith Observatory with reports of strange lights in the sky -
thousands of them.
We had no idea what people were talking about
until we got enough calls to realise what they were seeing...
..were the stars of the night sky.
Those strange lights may not mean much to us now,
but what's above is directly responsible for us being here today.
The road to civilisation began when prehistoric people looked to the skies
and learnt the concept of time.
(Ticking)
lt's hard to imagine anybody keeping track of time
without using the sky as the fundamental reference.
You see the seasons shifting with the appearances and disappearances of stars
and with the migration of the sun on the horizon and its changing angle at the height of day.
All of these things were probably so apparent tens, if not hundreds of thousands, of years ago
that they've just been engrained as a human habit for keeping track of time.
There were many cycles the ancients could study.
The sun, day by day, started with sunrise and ended with sunset.
But another, and even more important cycle, was the moon.
The nice thing about the moon is it changes every day.
lt moves in its position and it changes its appearance.
lt's bright, it's fairly large in the sky.
You can't miss it.
And you can't miss the way it changes from night to night.
sometimes it's a razor-thin sliver while other times it's a bright, shining disc.
We all know that the appearance of the moon changes - but why?
so why does the moon go through phases every month?
Well, the answer has everything to do with the position of the moon as it orbits the earth,
illuminated by the sun.
so here we see the moon located between the earth and the sun
and it's the back side of the moon that's illuminated by the sun,
so the side you see at the earth is dark.
We call this phase a new moon.
But as the moon orbits the earth, the side that's illuminated comes into your view.
The little sliver of light that you can see now gives this moon a crescent phase.
And then as the moon orbits the earth a little bit farther,
now the hemisphere that's illuminated is half seen by you at the earth.
We call this a quarter moon.
And then finally, as the moon orbits the earth yet farther,
now you can see the fully illuminated hemisphere of the moon,
and of course, we call that a full moon.
Nowadays, our calendars tell us when there's a new month.
But the word ''month'' comes from the moon cycle.
The time it takes the moon to complete a cycle around the sky is about 27 days.
That, if you look at it, is close to 28, which is the number 7 multiplied by 4.
so the lunar cycle actually gives rise to what we would call a month of four weeks of seven days.
This is a really obvious kind of pattern we could draw out of the sky.
You have something that allows you to count days, one after another and bundle them in sets.
That's actually the very core of timekeeping.
Having neat, little bundles of time allowed our ancestors to begin noticing patterns
or significant events that happened at certain times over the moon cycles.
One of the things about humans is that we are pattern-seeking beasts.
We see one thing and then something else happens and we say,
''Oh, when that happens, this always happens after it.''
The moon cycle gave the ancients a way to track a small amount of time - the month.
But then they began to notice longer patterns, like the seasons.
They saw how star formations and alignments moved,
and they could time these movements with seasonal changes.
You'd recognise certain collections of stars that will be up some time of year,
say just before the weather got warm and food became plentiful.
And other stars that were the harbingers of winter, when food was going to be scarce.
There are constellations that come up, like Orion,
and when you start to see that - hey, winter is coming.
so the seasons can be tied to the stars.
The ancients played connect the dots with the stars,
forming images we now call constellations.
l'm gonna create some random stars on our sky back here with this paint gun
and we'll create some constellations together.
Now let's connect some dots.
Human beings have a desire to impose order over randomness.
For instance, here l see a human figure.
The ancients also populated the sky with objects that were important to them -
livestock or animals.
lmportant to me is my sUV.
Now you may see something different in my stars than l did, but that's OK.
There's no limit to human creativity.
Regardless, we're both trying to do the same thing - impose order on chaos.
lt was studying these constellations as they moved throughout the sky
that allowed the ancients to track the seasons.
so why do different stars appear in the sky as the seasons change?
We make a complete orbit around the sun in a year, just over 365 days.
But both the appearance of certain stars and the seasons
have everything to do with the tilt of the earth.
Our planet spins around on an axis that's offset by about 24 degrees.
During the summer, the axis is angled towards the sun.
More sunlight means hotter temperatures and it also means we get a certain view of the sky.
But as earth continues in its orbit, the axis tilts away from the sun.
That's what gives us winter and a different view of the sky.
This cycle proceeds like clockwork, which is what made it so handy to our ancestors.
Developing the concept of seasons by looking at the patterns of the stars
puts you more in tune with your environment and allows you to plan for hunting and gathering
and all the other activities you need to survive.
The ability to predict changes in the environment meant our ancestors could adapt.
By adapting, they thrived.
This is a fundamental thing to allow a group of individuals
to go from being subject to the whims of the environment
to being able to build up a culture and a civilisation
that uses these changes to their own advantage.
With the ability to time major cycles, the ancients gained power over their environment,
and this power led them to build some of the most amazing monuments
in the history of mankind.
These days, you can't escape time.
lt's everywhere,. clocks on your computer, your mobile phone
and on the dashboard of your car.
Today, time can seem like a burden.
But for our ancestors it was the key to survival.
The fact that the sky had cycles we could predict is very important
because it meant that we had some way to understand the larger reality around us.
Understanding that reality prompted one of humanity's greatest leaps forward.
Using the stars to predict seasons
helped people drop the nomadic ways of the hunter-gatherer and settle.
You can imagine two different tribes.
One of them noticed that when certain stars were rising,
that's when they could plant crops, because that's when spring was coming.
The other one doesn't know this.
They don't look up or notice the stars; they just do whatever they want.
You know, which one of these is the more successful?
Well, the ones who study the sky.
They can feed their population, grow and become bigger,
and then they study the stars even more.
The ancients celebrated that success with enormous monuments
built to make incredibly careful observations of the sky.
There are many of these sites around the world. Perhaps the most famous is stonehenge.
When you're talking about ancient sites that might have something to do with astronomy,
it is hard to avoid talking about stonehenge.
Built on salisbury Plain in the south of England,
these circles of rough honed rock were built 4,500 years ago
in part, to observe and chart the solstice.
The most obvious astronomical alignment
is the summer solstice sunrise alignment over the Heel stone at stonehenge.
The solstices happen at six-month intervals and mark a very important astronomical shift
in the earth's alignment in relation to the sun.
Because our axis is inclined as we go around the sun,
that means that sometimes parts of the earth are actually tipped towards the sun
and have a more direct sunlight hitting them.
The summer solstice is when the Northern Pole
is tipped as far as it's going to tip towards the sun
and we're getting the most direct sunlight possible.
ln the winter solstice, the opposite is true.
The solstices were the longest and shortest days of the year
and they marked important turning points,
when the seasons of summer and winter were at their mid-points.
lt becomes, then, a reference point.
lt allows you to know where you've been and where you are going.
lt's believed stonehenge was used to measure these solstices.
As the sun approached the solstice, it would track along the blocks
until a beam of light illuminated the centre.
At the winter solstice, the sun sets between a pair of giant stone blocks,
directly above what's called the Altar stone.
During the summer solstice, the sun does the opposite
and shines through the Heel stone to illuminate the Altar.
Not only were the solstices indicators of the annual cycle between summer and winter,
they also gave humanity the means to time the year.
The date of the solstice never changes because the earth goes around the sun
in a wonderfully closed orbit.
lt always comes back to the same place.
so the summer solstice happens at the same time every year.
That was something ancient people could latch onto.
And virtually every one of them did it.
Cultures all over the world built massive monuments to track the solstices.
One fascinating example is Chaco Canyon,
a stone city in the American southwest built more than 1,000 years ago
by a mysterious people called the Anasazi.
Chaco Canyon is a place where a very sophisticated civilisation existed
that was able to develop monumental architecture
and was able to celebrate some of the symmetries they saw in the universe.
- so this is Casa Rinconada. - lt's amazing.
Astronomer Bryan Penprase is here with a student
because he believes that hidden within the geometry of these structures
are clues that illustrate the deep connection these people had with the skies.
lt's got almost this perfect symmetry.
Those two entrances... to find an axis of symmetry,
which is aligned almost perfectly with north-south,
plus there's an additional alignment with this window over here
and the summer solstice sunrise, which will light up one of those niches
as it enters in through the window.
As a cultural touchstone, today we take the sun for granted.
But what's clear from archaeological records... is that our ancestors did not.
ln those celestial rhythms, they saw evidence of some otherworldly power.
l think they saw in the enormity and the beauty and the clockwork of the universe
something beyond themselves.
lndeed, something spiritual.
And so l think notions of great gods and notions of the size and the behaviour of the universe
probably were quite closely linked.
Cultures and civilisations all over the world saw the same things in the sky
and developed similar mythologies to explain them.
The lnca, the Mayans, the Babylonians, and other ancient cultures
saw the skies as a divine realm,
populated by the gods that ruled over earth.
They all worshipped the night sky. They built enormous structures.
People bowed down to the grandeur of the cosmos
in the form of these architectural wonders
that were designed to pay homage to the night sky and its denizens.
Nowhere is this more evident than in Egypt's Great Pyramid.
There are interesting architectural details to the Pyramids,
and in particular, the Great Pyramid, the largest pyramid and probably the very best built.
4,600 years after it was built, the Great Pyramid remains one of the largest buildings on earth.
As big as seven city blocks and rising to around 1 50 metres,
it was built as a tomb for the Pharaoh Khufu.
An interesting astronomy has been attributed to the Great Pyramid,
which has some unusual architectural elements that you don't find in all of the Pyramids.
These ancient engineers who built this pyramid were able to arrange 2.3 million stone blocks,
each weighing about two and a half tons,
with an incredible level of precision.
They aligned this enormous structure so that each side faces one of the cardinal directions -
north, south, east, and west.
But what fascinated researchers is what was on the inside.
There are two shafts that just drive through these block walls of the Great Pyramid,
one to the north and one to the south.
Those two shafts point to two celestial destinations.
Or at least they used to.
Today these shafts don't line up neatly with any stars,
but nearly 5,000 years ago they did.
The shaft lines up where the North star would have been
and where the centre star of Orion's Belt would have been a long, long time ago.
lt's believed the shaft to the north
aligned with the star that would have been the North star thousands of years ago.
And the shaft to the south with another star in the constellation Orion.
That's not the case today,
because earth goes through a cycle where the tilt of its axes changes.
There was no North star because of the procession of the earth's axis,
which takes place over a time scale of 23,000 years.
We believe what they did is use one star from the Big Dipper
and one star from the Little Dipper,
which, if you drew a straight line between them, contained the point in the sky
about which all the stars rotated and aligned the Pyramids with that.
That point was the star Thuban, which the Egyptians associated with rebirth.
All those thousands of years ago, it would have been earth's pole star.
lf that's where the northern shaft pointed,
then the southern would have been aligned with the star in Orion's belt
that the Egyptians linked to Osiris, the God of Resurrection.
Even more important to science, by applying what we know of the 23,000-year progression,
we can run the clock backwards and discover exactly when the Great Pyramid was built.
We can use modern astronomical calculations to find out
when those two stars were aligned with the North Pole
and the result is that the Pyramids must have been designed around
2467 BC.
lt's kind of lovely to think how the human race decided that the stars were so important.
They're just little lights in the sky.
Yeah, they change position, there are cycles to them,
but we built our largest monuments -
things like stonehenge, the Pyramids.
They're aligned to the stars, they're related to them.
so somehow these faraway little lights took on cosmic importance.
stonehenge and the Great Pyramid -
these huge structures are a testament to how important the skies were to early civilisations.
But some believe these structures were too big and too precise
to have been built by such primitive people.
Could they have had a little help from visitors from the sky?
Once our ancestors settled, their fascination with the skies went into overdrive.
They built massive structures to make extremely detailed observations.
But the question is...why?
Why did the ancients construct such huge buildings to observe the skies
when they didn't have to?
lt's hard for me to understand why you build a gigantic monument out of stones.
That's the hard way to do it.
And l don't think you get budgets for astronomy to build things bigger than you need to do.
All sorts of mysteries surround the construction of these monuments and why they were built.
some theories suggest that instead ofjust observing the skies,
they might have been erected using knowledge from visitors from another world.
That's the idea behind the Ancient Astronaut Theory.
The Ancient Astronaut Theory tries to establish whether or not
extraterrestrials visited earth in the remote past.
Why do we think it's even remotely possible that people of prehistory were visited by aliens?
Because ancient texts from cultures around the world speak of mysterious beings
cruising the skies in chariots of fire and bringing humanity wisdom from the cosmos.
The Mahabharata, an ancient lndian epic, which is their equivalent of the Bible,
is packed with stories of gods, which a long, long time ago
flew around in marvellous golden sky ships, referred to as vimanas.
They were also very specific in mentioning that they are machines made out of metal.
lt describes their weaponry,
that some vimanas had the capability of cloaking themselves to become invisible.
All crazy science fiction-type stuff...
..but was it really science fiction?
That's the big question.
The south Americans, Asians, and Egyptians all have mythologies that speak of beings
who came to earth aboard cosmic eggs.
These cosmic eggs appear in virtually every single creation story of each culture
all around the world.
They all begin the same way, that one day the heavens opened and this silver cosmic egg
descended from the sky and these gods came out of these eggs
and taught mankind in various disciplines.
But not all stories of ancient astronauts come from historical texts.
One of the most bizarre legends comes from a tribe in North Africa,
who worship a star nearly 80 trillion kilometres away from earth.
The Dogon tribe in Northern Mali
have a wonderfully rich mythology centred on the star sirius.
sirius is the brightest star in the sky. OK, that kind of makes sense, but there's more.
The Dogon say that there is a dark companion to sirius.
The Dogon have believed this for nearly 1,000 years and there's more.
They claim that beings from this distant star have actually visited them.
The Dogons have a myth about aliens,
fish-like beings that lived in water that came to give them knowledge;
that came from this dark star.
Every 50 years, the Dogon celebrate the star's emergence from the far side of sirius.
And what's amazing is that star is there.
ln 1 862, astronomers confirmed its existence.
But there's no way the Dogon could have seen this dark star from earth.
We know that sirius, the Dog star,
has a faint stellar companion, but it's not something you can see with the naked eye.
lf this ball represents the faint companion to sirius,
than this searchlight back here represents sirius itself.
You can see that the companion is easily lost in the glare of the light of sirius,
and that's what makes it such a mystery
that the Dogon would have known about this companion many years ago.
so what explains the Dogon's knowledge of this unseen star?
ls it just coincidence?
No-one's quite sure,
but the Dogon aren't the only evidence cited as proof of alien contact with early cultures.
some claim that the buildings the ancients left behind
also offer evidence of extraterrestrial influence.
lf you look at stonehenge from a bird's eye perspective, you see all these concentric circles,
and one mathematician has found out that each circle corresponds with one of the planets.
so what we have here, basically, is a model of our solar system.
stonehenge is built with blocks of stone, some weighing as much as 50 tons.
They stand upright and some are stacked on top of one another.
lt would be difficult for modern people to build this.
What's more, scientists have learned these stones came from a quarry
hundreds of kilometres from stonehenge itself.
so...how did they get them there?
The legends behind stonehenge refer to star beings that arrived
and taught people how to move stones.
ln fact, one really mysterious story says that these stones levitated.
Now, do l think that happened?
l don't know, but it's a story and it's something worth looking at.
Then there's the Great Pyramid in Egypt.
Though controversial, some early surveys of the Pyramid
reveal an intriguing geometry in its construction.
The proponent's arguments run as follows.. 36,524 inches around.
Drop a decimal point between the 5 and the 2, and you've got the exact length of a solar year-
365.24 days.
Divide the circumference of the Pyramid by twice its height
and you get one of the most important mathematical constants, Pi,
accurate to six decimal places..
Pi is the ratio between a circle's circumference and its diameter,
and it's proven key to some stunning insights about the universe.
Eisenberg's Uncertainty Principle, General Relativity,
and Kepler's Law of Orbital Motion are all based on Pi.
What's more, Pi wasn't officially discovered until 2,000 years after the Pyramid was built.
Could the Egyptians really have discovered Pi so early?
some say it's evidence that these ancient people had help from above.
Of course aliens did not build the Pyramids.
lt was our human ancestors.
But our ancestors built the Pyramids with the assistance of the guardians of the sky,
otherwise referred to as the gods.
Most scientists don't think there's enough proof to believe in ancient astronauts
or visitors from beyond,
and that we need to give more credit to the power of human ingenuity.
But not everyone's ruling it out.
lt's nuts, but do we have to discredit everything that our ancestors put in stone?
l say no, and let's look at it from an alternative perspective and maybe, just maybe,
we will find the answers that we're all looking for.
These answers, it seems, are still shrouded in mystery.
The astronomy our ancestors practised and the ruins they left behind
make us wonder who these people were and how they achieved everything they did.
Though some believe their accomplishments are evidence of alien contact,
what's undeniable is, once they mastered the skies, our ancestors conquered the planet.
Not only did the skies above give the ancients the concepts of time
and plant the seeds for civilisation,
they also gave them the tools they needed to explore earth.
For millennia, the rhythms of the skies guided our ancestors on theirjourney to civilisation.
The cycles of the moon, sun, and other stars
gave them the power over an unforgiving environment.
The fact that the sky had cycles we could predict is very important
because a system of mathematics could be built up to predict it.
And from there, we began to explore the rest of the world.
Just as the skies gave early humans a way to mark and measure time,
they also provided them with the tools they needed to explore earth.
The Greeks knew something that we claim Columbus discovered -
that the earth was round.
The Greeks knew that very well. They, in fact, knew the circumference and the diameter.
2,500 years ago, a Greek mathematician named Eratosthenes
picked up a couple of sticks and used them to discover that earth was round.
What Eratosthenes was able to do 2500 years ago
with technology no more sophisticated than a stick is really quite remarkable.
Not only did he show clearly that the earth is a sphere,
he measured the diameter of that sphere to considerable accuracy.
How could he do that?
Let me show you with the help of my little happy face back here and my little toy gun.
so here's what Eratosthenes did.
He put a stick in the ground in syene in southern Egypt,
near where the Aswan Dam is today
and noted that on the summer solstice, there was no shadow cast by the stick,
the sun was directly overhead.
And yet he knew that on that same day in his hometown of Alexandria,
a stick would cast a significant shadow.
That's not at all what you'd expect on the surface of a flat plain.
All the sticks would have the same length of shadow.
But on the surface of a sphere, this is just what you'd expect.
Furthermore, by simply measuring the length of the shadow,
he could calculate the angle of the sun in the sky
and recognise the difference between the two angles
was exactly one-fiftieth of a complete circle.
Now, he also knew the distance between those two cities,
so simply multiplying by 50 gave him the circumference of the earth.
Eratosthenes calculated that earth was 24,662 miles
or 39,690 kilometres around.
The actual figure is 24,901 miles
or 40,07 4 kilometres.
He knew the circumference of the earth to within a few per cent of its present value,
an amazing discovery.
Not just that the earth is round, but, in fact, how big it is.
That discovery still ranks as one of the most important insights ever made about earth.
And it showed the ancients that the skies could be used for more than just keeping track of time.
They could also use the skies to explore the planet.
The Polynesians were able to use the stars
to navigate over hundreds and even thousands of miles
and they were in dug out canoes.
They would literally carve out a tree and make a catamaran or something like that,
and sail to Hawaii, or wherever they were going, and they did this using the stars.
Beginning about 3,000 years ago,
the Polynesians set out from what is today the island of Taiwan
on a migration that would, in the end, take them to the atolls and archipelagos,
from New Zealand to Hawaii.
They did it in small, open canoes with only the sun and stars to guide them.
lt's amazing what our ancestors accomplished, given the kinds of resources that were available.
These were highly intelligent, motivated people that were highly resourceful.
The result of that, example of that, and evidence of that
is the fact they found these islands.
Kalepa Baybayan is a traditional navigator with the Polynesian Voyaging society.
They're Hawaiians who sail using the same techniques
that brought their ancestors to Hawaii more than 1,000 years ago.
The sun is about 20 degrees north of east.
That's where it's coming on the horizon, so my hand is about 20 degrees wide.
Yeah.
so east is actually not where the sun's coming up, but where my fingertips are over here.
lf east is on our beam, then we're gonna be going north, yeah.
sunrise was key to Polynesian navigating.
They'd orientate everything to where the sun rose in the morning.
That's your best navigation tool at sunrise.
As the sun is rising, when l'm scanning the horizon, l'm seeing these swells out here.
lf you understand where the swells came from in relationship to where the sun rose,
then you can navigate the harder part of the day when the sun is high.
At night, these ancient voyagers used stars to guide them across the featureless ocean.
There were stars and constellations that they knew of and they tracked them across the sky,
just like the sun.
lt tells you these are great explorers.
They were calculating and were able to identify the clues that led them to these islands.
They were driven by great curiosity about the world they lived in.
lt's what got these people across earth's largest ocean
and they did it 300 years before the first European.
That may all sound like ancient history,
but techniques used by the Polynesians and all the mariners who followed
are still being used today.
The only difference is that we're exploring the surface of a different world.
For our ancestors, the skies were like a survival guide.
They guided them on voyages across earth and opened our planet to exploration.
And today, the skies are helping us explore the surface of other worlds.
The stars have been the foundation of navigation since people first looked up
and we used it during Apollo.
Even though they had computers and sophisticated navigational devices,
the lunar astronauts relied on the stars to guide them on their 400,000km-voyage to the moon.
l can't remember how many star sightings we might have taken,
but there's certainly no question that you are dependent on the stars,
you're dependent upon this machine, which is oriented with respect to the stars.
The electronic navigation system couldn't read all the tiny changes in course,
which, on such a long journey, could have had enormous consequences.
lf you're shooting a rifle and the target's only 50 feet away,
you can probably get near the bull's-eye.
But if it's out there, you know, half a mile away and you're trying to use the telescope,
l mean, a very, very slight change is gonna make a huge difference way out there.
(Bullet pings)
Being a marksman is a lot like being a lunar astronaut.
We're both shooting at targets very far away.
A little bit of difference at this end makes a lot of difference at that end,
and if l'm off on my trigger press, on my breathing by just a little bit,
l could completely miss the target.
Let me show you what l mean.
(Ping)
Let's go see how l did.
Now, l was shooting from 35 yards away
and as you can see, my bullet impacts are pretty much in the centre of the target,
except l've got one that's off to the left just a little bit.
That was because of something l did that wasn't quite as perfect as the other two,
and those little mistakes magnify themselves at distance.
so what would happen if we tripled the distance to the target? Let's go find out.
(Bullets ping)
You can see how at 35 yards, the bullets are almost touching,
but we tripled the distance and the shots start to spread out.
Now, l'm aiming at the same spot.
l'm holding dead centre of the blue circle and l'm trying to hit the centre,
but those tiny imperfections are causing errors the farther l get away.
Now you can see why astronauts had to constantly readjust their navigation,
because a little error makes a big difference a quarter-million miles away.
To stay on course,
the astronauts used the same tool navigators have used for hundreds of years -
a sextant.
What the sextant does is it basically lets you make very accurate measurements
about the angular separation between objects in the sky and the horizon.
And by taking a series of these measurements,
measuring certain stars and where they are above the horizon,
and comparing that to carefully tabulated tables,
you would be able to basically look up your geographical location
based on the location of the stars in the sky.
The sextant has been used by navigators ever since its invention in the 1 600s.
The way you would do it, actually, in Apollo...
..is you would essentially tell the computer, OK,
''Hey, point the sextant at some particular star,
point the sextant at Canopus.''
And it's... lt thinks it's right.
so it knows where Canopus is,
and it goes ''crrrrk'', and points the sextant in that direction.
Now, you look through the sextant, and here's the crosshairs, and Canopus is really over here,
instead of being at the middle of the crosshairs.
so what you do is you move the crosshairs up
or you move Canopus down into the crosshairs, and you mark.
And you say, ''That's where it really is, dummy.''
The Apollo astronauts would take several star sightings a day to correct their course.
Without the sextant, they might never have made it.
Anybody who's spent time with the stars has, forever, friends up there.
You know that when you look up again, there they're gonna be.
You can count on them.
That's as true now as it was back during the days of Apollo.
since touching down on Mars in 2004,
the Mars Rovers have been wandering the dusty surface,
probing the mysteries of the Red Planet.
And mission scientists have used the sun to tell these robots where to go.
You don't want it to fall in a crater. You don't want to bump into rocks.
You need to know which direction you're going,
so it's really important we know where the sun is.
Using methods similar to the ancient Polynesians thousands of years ago,
scientists take sightings of the sun
and use them to remotely drive the Rovers to explore the surface of Mars.
Then they use the sun to send all that data back to earth.
The Rover needs to know where it can look in the sky to find the earth.
so to do that, it... it looks for the sun.
The trajectory of our evolution,
from nomadic hunters to space explorers, was guided by the stars.
lts patterns and cycles pushed on a course
that would lead to everything we know and enjoy today.
We humans are simply asking the same questions,
maybe in a slightly more sophisticated way,
but we're trying to understand our spiritual and scientific place in the universe.
Astronomy prompts wonder.
Wonder prompts the quest to develop accurate,
more accurate descriptions of nature.
More accurate descriptions of nature are a tool for survival.
ln the known universe, the skies matter.
Without them guiding us on a journey from prehistory into civilisation,
we would never have known so much about our planet, the universe, and our place within it.
Astronomy is not a luxury, it's a necessity, and we still use it in different ways,
but we use it as energetically, as emphatically, as our ancestors ever did.
Who knows where the stars will take us next.
There are questions still remaining,
and the chances are the skies will once again help us to find answers.