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00:00High above our heads is a glittering panorama so vast and mysterious that we have spent all of human history trying to unlock its secrets.
00:14Why do the heavens move? And where do we fit among the planets and the stars?
00:31Looking for answers to these questions, we embark on a 2,000-year journey of discovery that would reshape our Earth and replace ancient stories with a new way of thinking.
00:55We invent incredible devices to map the heavens.
01:03And a few risk everything to work out our true place in the universe.
01:11This is the story of humankind's obsession with the skies and the ways our ancestors made sense of the universe.
01:25This is the story of how we move from a world ruled by supernatural beings to a cosmos revealed by scientific astronomy.
01:38This is the story of seeing other worlds and finding our true place among them.
01:45This is the story of our ancient skies.
02:03From the beginning of time, we have created stories to explain how the universe came to be and how it works.
02:10We have learned to watch the skies and to mark the passage of time.
02:20When the sun sets behind that landmark again, boom, you know you've been waiting one year.
02:25And ultimately, look into the future.
02:29But as different cultures began to share their observations and ideas,
02:34our assumptions about the nature of the cosmos began to unravel.
02:40For millennia, people across the world assumed the Earth was flat.
02:56Confined within a universe of limited size and shape.
03:01It does make sense that many of our ancestors believed that the Earth was flat.
03:05And that's because the Earth is so huge.
03:11It's really a matter of perspective.
03:16But a flat Earth didn't mean an infinite Earth.
03:20Because the sky was a dome, then the limit of the world could be found where Earth and sky met.
03:26Anyone brave enough to try and reach that limit had to enter the unknown.
03:39In ancient Greek epic, the hero Odysseus had to venture to the very limit of the world to find the land of the dead.
03:54The closer he came, the more he encountered terrifying dangers and deadly monsters.
04:09We entered the straits in great fear of mind.
04:17Knowing that on the one hand was Scylla.
04:22And on the other, the whirlpool, Charybdis.
04:27We could see the water whirling round and round, and it made a deafening sound as it broke against the rocks.
04:40The men were at their wits' end for fear.
04:45Scylla pounced down upon us and snatched up my six best men.
04:59But even as this story was being written down, there was evidence for those that looked that the world might not be flat after all.
05:17We spotted clues in the skies.
05:19In a lunar eclipse, the Earth comes between the moon and the sun.
05:25So instead of the moon being illuminated, the Earth's shadow blocks some of this light.
05:30And you can see the curvature in this shadow.
05:33We also noticed this much closer to home.
05:37If you've ever been out on the ocean and looked out on the horizon and saw a ship sailing away,
05:43the ship doesn't just fall below the horizon all at once.
05:45It's actually the hull that sinks below the horizon first and then the mast.
05:51From at least the 10th century BC, sailors were making incredible voyages over thousands of miles.
05:59And they found no limit to their world.
06:05The ancient Greek historian Herodotus even told a story about Phoenician sailors who circumnavigated Africa.
06:12But there was one part of that account he didn't believe.
06:18As their fleet rounded Africa, heading west, something unusual happened.
06:24The sun now appeared to their right.
06:28While it's clear now the sailors must have crossed the equator.
06:34For Herodotus, this made no sense.
06:39But this was just the sort of observation that could be used by other ancient Greeks,
06:44who were starting to think in a whole new way.
06:47In early classical Greek culture around the 500, 600 BCE, we begin to see the origin of what we now know as Greek science and philosophy.
07:01So what the Greeks begin then to do is to leave out the gods and goddesses and begin to focus on the material.
07:09We don't know if there was ever a Eureka moment, but by the 5th century BC, this massive eruption of Greek science and philosophy resulted in a reshaping of our Earth.
07:23So dramatic that even today, some find it difficult to accept.
07:34Our flat Earth broke free from the skies that contained it, reforming into a perfect geometric sphere.
07:43Our ideas about the universe would continue to change.
07:52But around Earth was no longer in doubt.
08:05The cosmos remained complex and mysterious.
08:08But when it came to the Earth, human ingenuity allowed us to move from questions of shape to those of scale.
08:18The question isn't, is the Earth round?
08:21The question really is, how big is it?
08:24A mathematician in Alexandria in Egypt took on the task of finding out.
08:29His name was Eratosthenes.
08:32Eratosthenes was the head of the library at Alexandria and most famous for having calculated the circumference of the Earth.
08:43The library at Alexandria had a remarkable ambition.
08:47To collect all the world's knowledge under one roof.
08:51When Eratosthenes arrived in Alexandria around 240 BC, the resources available to him were unique in human history.
09:05But the solution to the problem he faced was actually rather simple.
09:11So how do you calculate the diameter of the Earth when all you've got are the tools at hand and the ground around you?
09:17Eratosthenes heard a story that there is a well in Syene, Egypt.
09:28And on a certain day of the year, if you look down into that well, you can see all the way down to the bottom.
09:35The sun is shining straight down that shaft.
09:38Well, he lived in Alexandria, which was due north of Syene.
09:41And he knew that on that same day, a stick stuck in the ground still cast a shadow.
09:48And he realized that using simple geometry, he could use this information to calculate the circumference of the Earth.
09:55Eratosthenes knew that if he put a stick straight into the ground at the same time that somebody is looking down a well in Syene, this stick will cast a shadow.
10:04So if you measure the angle from the top of the stick to the tip of the shadow, that angle is going to be the same as the angle from the center of the Earth to Alexandria and Syene.
10:16Eratosthenes worked out that this angle was about 7.2 degrees.
10:23Using this figure and the distance between Alexandria and Syene, he could calculate the size of the Earth using geometry.
10:30Eratosthenes knew that Syene was 5,000 stadia south of Alexandria, and that's an ancient unit of measurement.
10:39When he did the experiment and did the math, he calculated that the circumference of the Earth was a little over 250,000 stadia all the way around.
10:49That's about 29,000 miles.
10:52Eratosthenes figure was just 16% more than the actual circumference of the Earth, which is around 25,000 miles.
11:04Making his incredible calculation one of the greatest feats of ancient science.
11:10For the first time in history, we knew how big the world was.
11:22But most of its surface remained a complete mystery.
11:27Over the following centuries, conquest, commerce and the growth of the Roman Empire connected countries as far apart as India and Italy.
11:38In Alexandria, a scholar named Claudius Ptolemy set out to map this new world.
11:47Unfortunately, he didn't have much to work with.
11:51Map making seems to have been pretty rudimentary in antiquity and relatively local.
11:58Lots of regional maps. We have very few maps that survive.
12:01Ptolemy worked out a way to unpeel and project our spherical Earth onto a flat map of the world.
12:10His methods and data were so good, they were used for over a thousand years.
12:15Even Christopher Columbus planned his voyages to the Americas based on Ptolemy's work.
12:23But mapping the Earth was dwarfed by Ptolemy's crowning achievement.
12:29An epic project. Using math and geometry to chart our vast and constantly moving heavens.
12:36And the starting point of this new map was one of the most fundamental ideas in ancient astronomy.
12:50Every year, we send hundreds of satellites into space.
13:05They orbit our Earth at up to seventeen and a half thousand miles per hour.
13:10Without them, modern life would grind to a halt.
13:20But this space-age technology effectively operates on an ancient idea.
13:27Satellites behave as if the planet they orbit is the center of the universe.
13:33It's a concept that's not quite as crazy as it sounds.
13:37We do not experience the Earth as moving.
13:41We experience the Sun as moving around us.
13:45It's experientially true. It's the world we live in.
13:49Wherever you stand on Earth, the skies and everything in them appear to move around us.
13:56For Ptolemy, this wasn't just a matter of perspective.
14:01It was a matter of fact.
14:03An Earth-centered universe.
14:07The first building block in a model that would shape our understanding of the skies for the next fifteen hundred years.
14:16Ptolemy combined the ideas of earlier astronomers with his own observations to build his model of the cosmos.
14:30And it relied on science, not the supernatural, to make it work.
14:41Ptolemy tried to create a complete system to explain everything in the universe, but on largely naturalistic grounds, without any need for divinities.
14:51No gods, no goddesses, just natural processes.
14:56Building out from the Earth, he believed that the heavens surrounding us were spherical too.
15:02It's another ancient idea that we still use.
15:06I am standing in one of my favorite kinds of places on Earth, a planetarium.
15:14And this is a model of how the sky works.
15:19We know that the sky is infinitely deep, but it appears to be as if it were a sphere surrounding us.
15:30We are in the inside looking out on the surface of one.
15:34And that's what this dome represents.
15:36The dome is the celestial sphere.
15:38The celestial sphere wasn't just a pretty metaphor.
15:43Something had to be holding the stars in their place.
15:48Ptolemy believed that the sphere was real, made out of a mysterious crystalline substance that couldn't be found on Earth.
15:57But not everything on the sphere moved in the same way.
16:01So if you were to go out at the same time every night, the stars would appear to be fixed and the planets would appear to be moving.
16:10And this is because the stars are so far away that they appear to be fixed points of light.
16:16The planets, on the other hand, are so much closer that we can see their motion and we can see how they change with respect to us from night to night.
16:24Ptolemy's model wouldn't work with just one sphere.
16:27Each celestial body would need a sphere of its own.
16:44First came the Moon.
16:48Followed by Mercury.
16:51Venus.
16:54The Sun.
16:55Mars.
16:57Jupiter.
16:59And Saturn.
17:01Beyond that, at the furthest reaches of space, were the stars.
17:07Ptolemy combined centuries of astronomy and math to show that movement in the skies was perfect.
17:16Locking the Sun, Moon and planets into circular orbits around the Earth.
17:21And finding a place for every object we could see.
17:33Ptolemy's motto was good enough to explain even the most unusual movements in the skies.
17:38If you just had circular motion and the objects are embedded in these spheres, then everything should be moving very neatly and nicely in a tidy fashion.
17:49But it turns out that's not the way the universe really works.
17:51If you go out and observe Mars night after night after night and measure its motion relative to the stars, on occasion it does something really peculiar.
18:01It slows down, it stops, it moves backwards, goes in a loop, and then starts moving forward again.
18:11Modern astronomers call this retrograde motion.
18:16To accommodate these strange movements, Ptolemy added another element to his model.
18:23The epicycle.
18:25An epicycle literally means a circle upon a circle.
18:30So if you have an object, say Mars, orbiting the Earth in a perfect circle,
18:35Mars is also making a smaller circle around that bigger circle.
18:39And that actually can help correct some of the motion that we see in the sky that doesn't fit with it moving in just a single circle around the Earth.
18:47Epicycles meant Ptolemy could explain retrograde motion.
18:53And alongside them, he introduced two other workarounds.
18:58Firstly, he argued that while everything moved around the Earth, it wasn't quite the mathematical center of the universe.
19:06Secondly, he added an imaginary point in space, near to the Earth, from where you could watch everything move in perfect circles.
19:17This was called the equant.
19:20Combined, they made his theories work in practice.
19:24To our modern eyes, Ptolemy's model looks extremely complicated.
19:31It's kind of easy to look back now at this Ptolemaic model with the Earth at the center of the universe,
19:37everything embedded in these crystalline spheres and these epicycles upon epicycles upon epicycles,
19:41and think, it's kind of ridiculous.
19:43The thing is, it worked, and you can show mathematically that if you add enough epicycles,
19:49you can actually predict the motions of all the objects in the sky pretty well,
19:54especially if you're just measuring it with your eye.
19:56Ptolemy's model worked so well, astronomers would cling to it for the next 1,500 years.
20:07But his cosmos didn't just live on paper.
20:09His ideas were turned into physical models to teach astronomy and to study the skies.
20:19At the Science Museum in London, physicist Dr. Harry Cliff has one example.
20:25This is an armillary sphere, and it's essentially a physical representation of the universe according to a Ptolemaic model.
20:35So in the middle of the armillary sphere, you've got this small brass sphere which represents the Earth,
20:41and then the next closest ring to that is the Moon.
20:46Beyond that you have the Sun, and then beyond that you have a band of fixed stars.
20:50So this only really shows the Earth, the Moon, the Sun, and the stars.
20:53The planets aren't included in this particular model.
20:56This armillary sphere is 500 years old.
21:00But the history of these objects goes back much further.
21:05There's evidence of armillary spheres going back to ancient Greece and ancient China,
21:10so around 2,000 years ago.
21:13So they're very ancient instruments, they've been around for a very long time.
21:16Armillary spheres were used for two different things.
21:19So one was to teach the principles of astronomy.
21:21But there are also larger armillary spheres that could be used for astronomical calculations.
21:26So for example, calculating the lengths of the day, the times of sunrise and sunset.
21:33Ptolemy's scientific model replaced the gods who once controlled the skies with cold, hard math.
21:43But, like most people across the Roman Empire,
21:46Ptolemy believed in astrology.
21:54The idea that the motions of planets and stars had a real impact on our lives on Earth.
22:00If people and stars and planets all exist as a single system,
22:06as you watch the stars and planets move mathematically, you can watch human life move.
22:11And if you can project astronomical movements into the future, the logic runs so you can predict what's going to happen to people in the future.
22:19What we see as superstition,
22:21What we see as superstition, Ptolemy viewed as science.
22:25He even dedicated an entire book to the theory and practice of astrology.
22:30He's saying the only reason why we need to be able to calculate the positions of stars and planets is so we know what their effects are on our lives.
22:41Practical astrology required the ability to predict the movements of the stars and planets.
22:49But to make these forecasts, astrologers needed reliable data.
22:55And Ptolemy's work provided the new gold standard.
23:00One of his great innovations was to really kind of lay out in detail his model, put it on a mathematical basis.
23:06His astronomy book contained these handy tables which allowed you to predict the motions of the planets,
23:13which was useful if you were an astronomer or if you were an astrologer, say in medieval Europe,
23:18where kings would make decisions about what they should do in terms of policy or going to war based on the positions of the stars and the planets.
23:25For the next 1500 years, decisions of life and death, even the fate of kingdoms and dynasties,
23:33lay in the hands of astrologers who relied on Ptolemy's model.
23:40Ptolemy was a citizen of the vast Roman Empire, which engulfed the Mediterranean and stretched from northern Britain all the way to Iraq.
23:54But 300 years after Ptolemy died and following centuries of superpower status, Rome was on the brink of collapse.
24:05The Roman Empire ceases to have the sort of command of the world that it did.
24:12Certainly by the fourth, fifth century, the world is no longer centered on Rome in the way that it was.
24:19The fall of Rome plunged Western Europe into chaos.
24:24Government fell apart.
24:27Economies crashed.
24:30Literacy retreated.
24:31The Dark Ages had arrived.
24:32But even as the lights went out in Europe, other civilizations still carried the torch of progress.
24:48I think that the story about the Dark Ages as being a period in which not much is happening is really wrong on a lot of levels.
24:56And one of the reasons that we've come up with this idea is because we've looked only at Europe.
25:01And I think that if we look in a broader global perspective, what we'll see again and again is that ideas are traveling across cultures.
25:10Astronomy was already well established in places like China and India.
25:14Now, they were joined by a new culture, also eager to study the skies, Islam.
25:24The Islamic world is an incredible flourishing of cultural and intellectual and scientific activity that we can't describe in any means as a Dark Ages.
25:36For hundreds of years, the East preserved classical knowledge that would otherwise have been lost forever.
25:42Until about the 12th century, the vast majority of Ptolemy, the works of Aristotle, the mathematical sciences of Greek antiquity were no longer accessible in Western Europe.
25:58Western Europe's loss was Islam's gain.
26:01This inaugurates what we know as the Golden Age of Islam, which runs for several hundred years.
26:09There's a fantastically vigorous scholarly culture in which all and any ideas about the nature of the cosmos are discussed.
26:16New observatories sprung up across the Islamic world.
26:28Using Ptolemy's system as their foundation, Eastern scientists map the skies with unparalleled sophistication, using a toolkit of specialized equipment.
26:38At Harvard University, David Unger looks after one example.
26:49Astrolabe is a combination between a calculator and a measuring device.
26:54So it allows you to calculate the position of the fixed stars, sun, other astronomical objects at any time on any date.
27:03The earliest surviving examples come from the Islamic world.
27:08This astrolabe was made in Persia around 1590.
27:12So an astrolabe is a two-sided device. On the backside is a measuring instrument. This would allow you to sight a star and get an angle of how far that star is or the sun up from the horizon.
27:27And then you could use that angle either to calculate distances or to set up the other side of the astrolabe properly.
27:35So the front of the astrolabe is really where the main action happens.
27:38It's a couple of layers on this base layer. There is a projection of the sky and a grid drawn on the sky projected down to this flat surface.
27:47And then above that is a layer that turns with these markers. Each marker indicates a different star.
27:54And then this ring represents the movement of the sun.
27:58And so over the course of the day, this upper ring rotates around showing you how the fixed stars appear to move across the sky.
28:08Using instruments like the astrolabe, Islamic astronomers added their own observations to the data accumulated over centuries of research.
28:19Some worked to polish Ptolemy's model, adding new calculations to keep it running.
28:25But others had more radical ambitions, and they searched for new ways to strip away Ptolemy's workarounds.
28:34The Ptolemy's model is the received model that has worked really well for a long time.
28:40And yet it's messy, these equants, these epicycles.
28:43Ugh! It's really hard to work with.
28:46So people start to simplify the calculations to reduce the number of epicycles.
28:53They wanted to get back to the fundamentals of ancient astronomy and the idea that objects in the sky moved in perfect circles.
29:03From the 11th century onwards, through trade and warfare, Islamic translations of the ancient texts began to return west.
29:16But they were entering into a landscape that had been transformed by the dominant force in Europe.
29:30Christianity.
29:31When it came to astronomy, although they'd lost Ptolemy's science, his model still endured.
29:44Because over time, Christians had found ways to fit this model into their own beliefs.
29:50In the Christian cosmos, the crucial factor is that everything is created and ruled over by God.
29:57Particularly in the maps from the Middle Ages, these world maps, we see them imagining God outside the sphere of the fixed stars.
30:06And so in that sense, conceptually, God encompasses the cosmos.
30:11Because heaven has to be somewhere, then people conventionally located heaven beyond the realm of the stars.
30:23And if God needed a physical place in the universe, then Satan needed one too.
30:32Ptolemy's model had the perfect solution.
30:36Hell would have been somewhere in the center of the earth.
30:42To explain Satan's place in the cosmos, the church turned to scripture.
30:50There was war in heaven.
30:53Michael and his angels fought against the dragon.
30:58And the dragon fought and his angels, and prevailed not.
31:04Neither was their place found anymore in heaven.
31:11And the great dragon was cast out.
31:18That old serpent, called the Devil and Satan, which deceiveth the whole world.
31:29He was cast out into the earth, and his angels were cast out with him.
31:42Now, with God and the Devil firmly in their place,
31:48The return of Ptolemy's written work helped us cement the Christian vision of the cosmos.
31:55And reveal the mathematical perfection of God's universe.
32:03This rediscovered knowledge soon embedded itself in beautiful objects and incredible machines.
32:10Like the world's oldest working astronomical clock.
32:15The Orloi in Prague.
32:19Whatever the weather, crowds gather to watch its hourly performance.
32:25But this is more than just a clock.
32:32If you know where to look, it's a guide to the cosmos.
32:37It uses an astrolabe showing the horizon of Prague.
32:41And the position of the sun and moon as they move through the zodiac.
32:47Watchmaker Dr. Gunter Erstman has spent 30 years studying astronomical clocks.
32:56He's going behind the scenes at the Orloi.
33:00I've never seen it before.
33:05The astronomical clock in Prague was built around 1410.
33:12Only very, very few original parts are still remaining.
33:16The oldest part is the stone carved rim of the astrolabe outside.
33:21From its earliest days, there's always been more to the Orloi than astronomy.
33:27The importance of an astronomical clock was not so much its elaborate indications or its intricate construction.
33:36It was a matter of prestige.
33:39It was top-notch technology or pride of scientific achievement and craftsmanship,
33:47which had, of course, an astronomical content.
33:49But there were only very, very few people who actually could understand the meaning of an astronomical dial.
33:56Something like the clock in Prague is a demonstration of the prowess of the ruler who lives there,
34:04that this is cutting-edge science.
34:06The money and know-how poured into the Orloi was evidence of a trend sweeping across Europe.
34:13Starting in the 14th century, Western Europe embarked on a golden age of learning.
34:22Fueled by the rediscovery of classic art, literature, and science.
34:29The Renaissance.
34:35But alongside a respect for the past, the Renaissance fostered radical new thinking.
34:46Where revolutionary ideas can come from unlikely places.
34:52Like the desk of a church official named Nicholas Copernicus.
34:59Copernicus travels to Italy because he's traveling in part to the heart of Renaissance Europe.
35:07And he's learning the cutting-edge approaches to texts and approaches to science that go with that.
35:13Copernicus was raised on Ptolemy's model of the cosmos.
35:17But he had also encountered the work of Islamic astronomers.
35:21And his studies convinced him there was a simpler way to explain the skies.
35:28He is exactly replicating the work of Islamic mathematicians.
35:35And attacking the monstrosity of the Ptolemaic system.
35:40Copernicus took what he learned in Italy, back home to Poland, where he set up his own observatory.
35:49As his work progressed, he became more and more convinced that Ptolemy's cosmos wasn't just too complicated.
35:56It was fundamentally flawed.
35:59And rather than repair this creaking model, he would replace it entirely with a revolutionary new theory.
36:10He's got great views of the stars where he is.
36:13And he's measuring precisely their locations in the sky and recording them and performing calculations.
36:18And this becomes sort of the data for him that helps him to justify his model of the cosmos.
36:25In 1543, just months before his death, Copernicus went to press.
36:35His radical new idea dared readers to question centuries of established thought.
36:43The Earth lost its place at the center of the cosmos.
36:53Finally, joining the other planets.
36:57As they orbited around the glowing heart of Copernicus's model.
37:03The Sun.
37:05After decades of hard work, Copernicus had changed the universe.
37:21But no one seemed to notice.
37:33Copernicanism is not inflammatory at the beginning.
37:39Some people have even gone so far as to say that Copernicus's De Revolutionibus in the 16th century was the book that no one read.
37:47It doesn't cause a stir.
37:49Copernicus's new model didn't change what we saw in the skies.
37:57Complicated math and naked eye observations could only take our understanding so far.
38:05Breaking this deadlock required a revolutionary new invention.
38:13One that would change astronomy forever.
38:17The telescope.
38:19The telescope is this moment where scientific investigation changes.
38:31And it's not just about the observer.
38:33Now it's about the instrument as well.
38:35And this is actually a pretty monumental shift.
38:41This is the first scientific instrument that extends the human senses.
38:47Telescopes have transformed our knowledge of the universe.
38:53Revealing the distant secrets of space to anyone who cares to look.
38:59But the invention that rewrote our understanding of the skies started off with more humble ambitions.
39:07In 1608, Hans Leverhey invents the Dutch spyglass.
39:21He's able to magnify things and he's presenting this to be sold and patented in the Dutch Republic.
39:29The spyglass was good for spotting ships.
39:37Or surveying landscapes.
39:39But not much else.
39:41When word of this creation reached Venice in Italy,
39:45a genius showman scientist spotted an opportunity.
39:49His name was Galileo Galilei.
39:53In Venice, Galileo hears about the Dutch spyglass
39:57and he decides that he's going to improve it.
39:59And he's going to get famous for doing it.
40:01Galileo realized that this primitive telescope could transform the way we looked at the skies.
40:09The objects that we can see in the sky are limited by the size of our eye
40:13and the size of the lens in our eye.
40:15Telescopes are a means of creating a bigger lens,
40:18allowing us to catch more light or more photons from space to observe these objects.
40:23The kind of telescope Galileo used was called a refracting telescope.
40:29Refraction just means bending.
40:31You use lenses to bend light.
40:33There are a couple of different kinds.
40:35There's the convex kind which bulges out and the concave kind which bulges in.
40:41With a convex lens, the light is coming in from one side and it's focused down to a point.
40:47And the problem with that is you can't focus it.
40:49You need those light rays to be parallel when they enter your eye.
40:52Well, that's where the concave lens comes in because this is a diverging lens.
40:56Light coming in from here spreads out.
40:59So if you get these two things at just the right distance, this one will converge the light,
41:04this one will diverge it, they balance out, and the light that leaves the eyepiece is then parallel
41:09and goes into your eye and you wind up getting a nice, focused, magnified image.
41:18Hungry for fame and riches, Galileo set about making the world's finest lenses for his game-changing telescope.
41:28The quality of the image you're getting depends on a lot of things.
41:31You have to have the lens ground to just the right figure.
41:34You've got to have high-quality glass.
41:36This is hard to do.
41:38Not only was Galileo worried about the optical design of his telescope,
41:42he had to worry about how the lenses were made.
41:44He did this himself.
41:45He actually improved the process, making sure that whatever he had was the best that anybody had anywhere.
41:52Within a year, Galileo built a telescope that packed an unprecedented 20 times magnification.
42:02Pointed towards the skies, we could now see further than any human had before
42:09and instantly reveal new truths about our universe.
42:15In 1609, Galileo turns his telescope to the skies and he begins to look at many things.
42:21He looks at the surface of the moon.
42:27The surface of the moon, Galileo sees through his telescope, is not a perfect crystalline sphere.
42:32It has mountains.
42:33It is rough.
42:37Galileo sees the matter of the moon to be similar to the earth.
42:43And perhaps if the matter on the earth and the moon are the same, motion works similarly in the heavens as it does on the earth.
42:50Galileo's telescope also revealed to him entirely new objects in the skies.
43:07With his telescope, Galileo was able to observe for the first time that Jupiter had moons orbiting around it,
43:12something that couldn't be seen with the naked eye.
43:15This marked a major advance in astronomy because for the first time scientists saw that the earth wasn't the only object with moons orbiting around it.
43:24One of Galileo's great proofs, what he sees as the ultimate proof of the Copernican cosmos, is when he turns his telescope to look at Venus.
43:34He sees that Venus is undergoing phases like the moon.
43:43So Venus isn't just solid all the time.
43:45Venus waxes and wanes.
43:46For him, this shows that Venus is inside the orbit of the earth and is also orbiting around the sun.
43:53That it's not just that the earth is orbiting around the sun, but that the other planets are as well.
44:05Armed with his telescope, Galileo had made more discoveries than generations of astronomers combined.
44:15And he was now certain that he held proof that the Church's official model of the cosmos was wrong.
44:24From 1610 onwards, word of Galileo's discoveries spread.
44:37Setting him on a collision course with one of the most powerful institutions in history.
44:46The Roman Catholic Church had attached itself very strongly to the Ptolemaic model of the universe.
44:54And also to whatever cosmology it could extract from the Christian Bible.
45:00The problem is, the Bible isn't clear about the structure of our cosmos.
45:05Instead, the Church had simply interpreted a handful of enigmatic verses to support its earth-centered model.
45:15Certain passages in Joshua talk about the sun standing still.
45:20And that means that the sun must normally be moving except when God intervened to stop it.
45:26As far as the Church was concerned, this supported their position that everything, including the sun, moved around the earth.
45:36By questioning this model, Galileo was also questioning the authority of the Church.
45:42And the importance of God's creation in the cosmos.
45:55Humanity loses its position of centrality.
45:58So philosophically, and potentially theologically, this is quite radical.
46:02This was a risky time to hold unusual views.
46:07The Catholic Church was struggling to contain the explosive growth of rival Protestantism.
46:20In this paranoid atmosphere, those foolish enough to question the established order could expect little mercy.
46:29In 1600, astronomer Giordano Bruno was burnt at the stake for his unorthodox ideas.
46:39But Galileo wasn't one to keep his mouth shut.
46:42This is a really important thing to understand about Galileo, about his personality, which is that he's a deeply ambitious person.
46:49It's not enough to do something. He wants to be recognized for doing it.
46:54So, to promote himself as one of the world's greatest scientists, Galileo wrote piles of correspondence publicizing his telescope and the implications of what he'd seen.
47:06But by putting pen to paper, Galileo was playing a dangerous game.
47:18One incriminating letter was recently rediscovered in the archives of the Royal Society in London.
47:25It's the job of Keith Moore to safeguard this historic artifact.
47:31This is a letter sent by Galileo.
47:37This is where he begins to talk about his ideas of heliocentrism and the way that scriptures are used to justify arguments and cosmology.
47:48It isn't particularly the scientific view, but it's the idea that the Bible is in the interpretation of the Bible by the Roman Catholic Church.
47:58It may be wrong.
48:00It was one thing to debate scientific theories.
48:05But in this letter, Galileo was questioning the church's reading of the Bible.
48:10So, particularly, he says things like, you kind of go to the Bible and cherry-pick small passages from it in order to talk about science.
48:23Science was a thing in itself.
48:25A copy of the letter was picked up by the Roman Inquisition.
48:35A tribunal set up to root out dangerous ideas and eliminate threats to the church by any means necessary.
48:44Galileo was now in their sights.
48:52He promised their evidence was forged by his rivals and sent the Inquisition a toned-down version.
49:00It was never known if Galileo was lying, until now.
49:04So, the significance of this letter is that it places the responsibility for the arguments that were circulating in 1613 to 1615 in Galileo's hand.
49:19The crossings out in corrections clearly reveal Galileo's hasty rewrite.
49:26This letter is important because this seems to be the evidence, the smoking gun if you like, that Galileo did indeed take back the letter to make it more acceptable to the Catholic Church.
49:38On this occasion, Galileo got away with a slap on the wrist.
49:45But the church had woken up to the challenge posed by new scientific ideas.
49:50Galileo was forbidden from teaching the theory of a sun-centered cosmos.
49:55And the writings of Copernicus were banned altogether.
50:05For over a decade, Galileo kept his ideas on ice.
50:11Then Galileo catches what he sees to be a lucky break.
50:16One of his friends and patrons, Maffeo Barberini, is elevated to the office of Pope Urban VIII.
50:24Galileo has a friend in the highest office in the land, and he thinks he therefore has a certain amount of leeway.
50:30He starts writing his dialogue concerning the two chief world systems, Ptolemaic and Copernican.
50:37By presenting two models of the cosmos side by side, Galileo hoped to avoid a visit from the Inquisition.
50:47But it was a huge miscalculation.
50:51He was summoned back to Rome and put on trial.
51:02On June 22nd, 1633, Galileo was found guilty of heresy.
51:10The outcome of the trial is that Galileo was placed under house arrest for the rest of his life.
51:19At his villa in Archetri, he's told not to write or publish about Copernicanism ever again.
51:29The Catholic Church maintained its ban on sun-centered theories for almost 200 years.
51:41But the genie would not go back in the bottle.
51:44And this time, Galileo didn't stay quiet.
51:49He spends his time in Archetri leveraging a network of contacts and disciples across Europe to publish his two new sciences instead.
51:58Which is the physics behind Copernicanism.
52:02The physics that will prove this Copernican philosophy.
52:07The telescope meant that anyone could now look at the skies and see what Galileo had seen.
52:15His voice was joined by those of other astronomers embracing and sharing fresh ideas.
52:24Together, their research ushered in a new era of scientific astronomy.
52:35They would finally overturn the ideas of old.
52:41And bring us ever closer to a true understanding of our skies.
52:49How do we remember what Galileo has seen?
52:51The physics has done and the instructions over the sky.
52:54Where we'd now give you hope.
52:57What I was seeing point- altre are these of the past?
52:59The science is after the galaxy's famous.
53:01We're hereORDIN KNOWLEDGE.
53:02The science data is the future of life.
53:05If we have the best 지que of life.
53:06And it'll be ever more.
53:08We see the technology.
53:09We're there.
53:10And we're here.
53:11And we're here.
53:12We're here.
53:13We're here.
53:14We're here.
53:15We're here.
53:16We're here.
53:17Enemoro.
53:18You