NARRATOR: EVER SINCE THE DAWN OF HUMANITY, THE SKIES HAVE INFLUENCED EVERY PART OF OUR LIVES.

THEY HAVE HELPED US TO NAVIGATE... MAN: FOR OUR ANCESTORS, THAT WAS THEIR NEIGHBORHOOD.

NARRATOR: TO BUILD... MAN: THE PYRAMIDS ARE ALIGNED PRECISELY TOWARDS TRUE NORTH.

NARRATOR: AND DEFINED THE VERY IDEA OF TIME ITSELF.

MAN: WHEN THE SUN CROSSES THE HORIZON, BOOM!

YOU KNOW YOU'VE BEEN WAITING ONE YEAR.

NARRATOR: TO EXPLAIN THE MOVEMENTS OF EVERYTHING ABOVE US, WE POPULATED THE COSMOS WITH GODS AND MONSTERS.

WOMAN: THE SKY WAS UNDERSTOOD AS A KIND OF STONE TABLET ON WHICH THE GODS INSCRIBED THEIR MESSAGES.

NARRATOR: BUT AS WE LOOKED DEEPER INTO THE HEAVENS... WE TURNED AWAY FROM BELIEF IN A MYTHICAL UNIVERSE... TO A RADICAL NEW WAY OF THINKING.

MAN: THESE PHENOMENA CEASE TO BE LINKED TO SUPERNATURAL GODS AND INSTEAD BECOME NATURAL.

NARRATOR: THIS IS THE STORY OF HUMANKIND'S OBSESSION WITH THE SKIES... AND THE WAYS OUR ANCESTORS MADE SENSE OF THE UNIVERSE.

THIS IS THE STORY OF HOW WE MOVED FROM A WORLD RULED BY SUPERNATURAL BEINGS... TO A COSMOS REVEALED BY SCIENTIFIC ASTRONOMY.

THIS IS THE STORY OF SEEING OTHER WORLDS... AND FINDING OUR TRUE PLACE AMONG THEM.

THIS IS THE STORY OF OUR ANCIENT SKIES.

♪ NARRATOR: TODAY'S TECHNOLOGY ALLOWS US TO SEE THE UNIVERSE IN WAYS THAT WERE UNIMAGINABLE EVEN A FEW DECADES AGO.

WE CAN OBSERVE FAR-OFF GALAXIES, MILLIONS OF LIGHT-YEARS AWAY... ANALYZE THE CHEMICAL COMPOSITION OF DISTANT PLANETS... AND EVEN WITNESS THE BIRTH OF STARS.

WE KNOW THAT THE MOON IS ORBITING THE EARTH AT 2,000 MILES PER HOUR... AND THAT THE MYRIAD OF PIN-PRICKS OF LIGHT IN THE NIGHT SKY ARE GIANT BURNING SUNS, PERHAPS EACH WITH ITS OWN SET OF PLANETS.

THE SKY IS NO LONGER A MYSTERY IN THE WAY IT WAS TO GENERATION AFTER GENERATION THAT CAME BEFORE US.

AND YET, WHEN WE LOOK UP AT IT WITH THE NAKED EYE, WE ARE STILL FILLED WITH THE SAME AWE AND WONDER THEY MUST HAVE FELT HUNDREDS...

EVEN THOUSANDS OF YEARS AGO.

♪ FOR OUR ANCESTORS, THERE WAS NO SEPARATION BETWEEN EARTH AND SKY.

TOGETHER, THEY FORMED A COSMOS THAT WE SHARED WITH THE SUPERNATURAL BEINGS THAT WE BELIEVED WERE AN INTEGRAL PART OF ITS WORKING.

MYTHOLOGY AND RELIGION ARE ALMOST ESSENTIAL WAYS OF EXPLAINING THE COSMOS.

NARRATOR: IN ANCIENT EGYPT, THE SKY WAS PERSONIFIED BY THE GODDESS NUT, WHO CURVED HER BODY OF STARS OVER THE EARTH.

AND THE MOON WAS ASSOCIATED WITH THE GODS THOTH AND KHONSU.

THESE SUPERNATURAL BEINGS ALSO INHABITED THE STORIES WE TOLD ABOUT HOW THE UNIVERSE ITSELF CAME TO BE.

CAMPION: WE EXPLAIN THINGS WE CAN'T UNDERSTAND THROUGH USING STORIES, BECAUSE NONE OF US REALLY CAN COMPREHEND HOW THE UNIVERSE STARTED.

NARRATOR: THERE ARE STORIES TO EXPLAIN THE ORIGIN OF THE COSMOS FROM ALL OVER THE WORLD.

FOR THE AZTECS OF CENTRAL AMERICA, IT WAS THE GODDESS COATLICUE WHO GAVE BIRTH TO THE MOON AND STARS.

FOR HINDUS, THE GOD BRAHMA SAT ATOP A LOTUS FLOWER AS HE CREATED THE EARTH, THE SKY, AND THE HEAVENS.

AND IN CHINESE MYTHOLOGY, A HAIRY BEAST CALLED PANGU EMERGED FROM A COSMIC EGG AND DIVIDED THE FORCES OF YIN AND YANG INTO EARTH AND SKY.

BUT OUR EARLIEST SURVIVING CREATION MYTH DATES BACK ALMOST 4,000 YEARS, TO THE ANCIENT BABYLONIANS.

IT'S CALLED THE ENUMA ELIS.

♪ THE ENUMA ELIS TELLS THE STORY OF A COLOSSAL BATTLE BETWEEN TIAMAT, THE PRIMORDIAL GODDESS OF THE SEA, AND THE GOD MARDUK.

WOMAN: MARDUK IS DESCRIBED IN EXTRAORDINARY TERMS.

HE'S GOT FOURFOLD VISION, HE'S GOT THE AURA OF 10 GODS, HE'S UNFATHOMABLE AND UNVISUALIZABLE IN HIS SPLENDOR.

[THUNDER] DIFFERENT WOMAN: MARDUK TOOK UP THE MACE... AND HELD IT IN HIS RIGHT HAND.

♪ TIAMAT AND MARDUK DREW CLOSE FOR BATTLE... AND LOCKED IN COMBAT.

TIAMAT OPENED HER JAWS... [ROARING] BUT WITH HIS MERCILESS MACE... MARDUK CRUSHED HER SKULL.

NARRATOR: THE BATTLE BETWEEN MARDUK AND TIAMAT EXPLAINED THE CREATION OF THE EARTH AND OCEAN, THE SKY AND EVERYTHING IN IT.

AL-RASHID: IT DIVIDES THE UNIVERSE INTO A TOP AND A BOTTOM.

WE HAVE THE SKY AND THE EARTH, AND AS PART OF THE EPIC, AND AS PART OF MARDUK'S ROLE IN IT, HE CREATES THE STARS AND THE CONSTELLATIONS.

HE FILLS THE SKY WITH ALL THE THINGS THAT ARE OBSERVED IN IT.

NARRATOR: TODAY, WE CAN STILL GET A GLIMPSE OF THE COSMOS AS THE BABYLONIANS SAW IT... FROM THE OLDEST WORLD MAP EVER DISCOVERED.

ETCHED IN CLAY OVER 2,500 YEARS AGO, IT SHOWS THE EARTH AS A FLAT DISC, FLOATING ON THE OCEAN.

♪ THE BABYLONIANS IMAGINED THEIR FLAT EARTH AT THE CENTER OF THE UNIVERSE, WITH EVERYTHING IN THE SKIES REVOLVING AROUND IT.

♪ BELIEF IN A FLAT EARTH WAS COMMON TO MANY CIVILIZATIONS ACROSS THE WORLD... FROM THE FAR EAST OF ASIA... TO AFRICA... AND THE AMERICAS.

FROM THE POINT OF VIEW OF OUR ANCIENT ANCESTORS, A FLAT EARTH MADE PERFECT SENSE.

MAN: WE KNOW THAT THE EARTH IS A BALL AND IT'S SPINNING ONCE A DAY.

BUT THE THING IS THAT'S NOT OBVIOUS.

IF YOU GO OUT WITHOUT REALLY THINKING ABOUT THAT AND JUST LOOK AT THESE MOTIONS, IT FEELS LIKE THE EARTH IS FLAT AND IT FEELS LIKE THE SKY IS WHEELING AROUND YOU.

NARRATOR: WE CAN IMAGINE THAT THE SKIES MUST HAVE BEEN AN ENDLESS SOURCE OF WONDER AND MYSTERY.

A PLACE TO BE ADMIRED AND INTERPRETED.

AND NO MATTER HOW FAR BACK WE GO IN OUR HUMAN STORY, WE FIND EVIDENCE OF OUR OBSESSION WITH THE HEAVENS.

NESTLED DEEP WITHIN THE HILLS OF NORTHERN SPAIN ARE THE CAVES OF EL CASTILLO.

HERE, OVER MILLENNIA, STONE AGE ARTISTS DECORATED THE WALLS WITH HUNDREDS OF PAINTINGS.

DR. JESUS GALLEGO IS AN ASTROPHYSICIST, BUT HE HAS SPENT YEARS STUDYING THE IMAGES THAT LINE THE WALLS OF THESE CAVES.

GALLEGO: SOME OF THEM ARE AS OLD AS 40,000 YEARS.

IF THIS IS CORRECT, WE WILL BE RIGHT NOW IN FRONT OF THE OLDEST PAINTINGS OF THE WORLD.

I AM SURROUNDED BY ABOUT 30 HANDS.

WE ESTIMATE THAT 20 BELONG TO WOMEN AND 10 BELONG TO MEN.

I LOVE TO CONSIDER THE POSSIBILITY OF THESE PEOPLE JUST LEAVING THE CONTOUR OF THEIR HANDS... TO LEAVE SOMETHING FOR US, THE PEOPLE OF THE FUTURE.

NARRATOR: DR. GALLEGO BELIEVES THAT WHOEVER PAINTED THESE PICTURES RECORDED THE THINGS THAT WERE MOST IMPORTANT TO THEM.

GALLEGO: OUR ANCESTORS WERE PEOPLE THAT WERE LIVING VERY CLOSE TO NATURE.

SO, IT'S NOT A SURPRISE THAT THESE PEOPLE REPRODUCED ANIMALS ON THE WALLS OF THE CAVES.

NARRATOR: HIDDEN AWAY IN ONE CORNER OF EL CASTILLO ARE A SET OF PAINTINGS THAT, AS AN ASTROPHYSICIST, DR. GALLEGO FINDS PARTICULARLY INTRIGUING.

GALLEGO: SOME PEOPLE BELIEVE THAT HERE WE HAVE A REPRESENTATION OF AN ASTRONOMICAL MOTIF WHICH IS VERY IMPORTANT, WHICH IS THE MILKY WAY, A SEQUENCE OF FAINT STARS ALL TOGETHER AND MAKING ONE SINGLE BODY.

NARRATOR: OTHER PAINTINGS HERE COULD ALSO HAVE AN ASTRONOMICAL ASSOCIATION.

GALLEGO: SOME OF THE CURRENT RESEARCHERS IDENTIFY HERE A SEQUENCE OF ASTRONOMICAL EVENTS THAT COULD BE RELATED WITH MOON PHASES, WITH DIFFERENT DAYS OF THE MONTH.

THIS IS ONE OF THE BEST LINKS THAT WE CAN FIND IN THE CAVE RELATED WITH ASTRONOMICAL PHENOMENA.

NARRATOR: THESE ARE THE EARLIEST PAINTINGS YET DISCOVERED THAT COULD DEPICT THE HEAVENS.

♪ IN TIMES WHEN WE RELIED ON THE NATURAL WORLD FOR OUR SURVIVAL... READING THE SKIES COULD GIVE OUR ANCESTORS THE EDGE.

IF YOU GO OUT UNDER THE NIGHT SKY EVERY NIGHT AND LOOK AROUND, YOU EVENTUALLY BECOME FAMILIAR WITH THE PATTERNS IN THE SKY, JUST LIKE YOU DO IN YOUR NEIGHBORHOOD.

YOU KNOW WHERE THE TREES ARE, WHERE THE BANK IS, WHERE THE MOUNTAINS ARE, AND THIS IS EVEN MORE TRUE FOR OUR ANCESTORS, FOR ANCIENT PEOPLES.

THEY WERE FAMILIAR WITH THOSE STARS.

THAT WAS THEIR NEIGHBORHOOD.

NARRATOR: OUR ANCESTORS WOULD HAVE SEEN THE SUN RISING AND SETTING IN THE SAME DIRECTIONS EVERY DAY... AND USED THE POSITIONS OF SUNRISE AND SUNSET TO ORIENT THEMSELVES.

BUT EVEN WHEN THE SUN WENT DOWN, THE STARS STILL HELPED US FIND OUR WAY.

PLAIT: WHEN WE LOOK UP AT THE SKY, ALL THE STARS APPEAR TO BE CIRCLING.

THEY'RE WHEELING AROUND A POINT FIXED ON THE SKY ITSELF.

WE CALL THOSE THE CELESTIAL POLES-- THE NORTH AND SOUTH CELESTIAL POLES.

AND ALL THE STARS APPEAR TO MOVE AROUND THEM.

NARRATOR: BY LOCATING THESE FIXED POINTS IN THE NIGHT SKY, OUR ANCESTORS COULD FIND THEIR BEARINGS.

BUT THE REGULAR MOTION OF THE HEAVENS ALSO MADE US CONSCIOUS OF SOMETHING COMPLETELY FUNDAMENTAL TO HOW WE ORGANIZE OUR LIVES--TIME.

THERE ARE 3 BASIC CYCLES IN ASTRONOMY IF YOU'RE OUTSIDE LOOKING UP AT THE SKY WITH YOUR NAKED EYE.

ONE OF THEM IS THE DAY-NIGHT CYCLE...24 HOURS.

THE NEXT ONE IS HOW LONG IT TAKES THE MOON TO GO AROUND THE EARTH.

IT GOES THROUGH A CYCLE OF PHASES FROM NEW TO HALF FULL TO FULL TO HALF FULL AGAIN AND BACK TO NEW.

SO, THAT GIVES YOU A WAY OF MEASURING SOMETHING LIKE ONE MONTH OF TIME.

NARRATOR: THERE'S EVIDENCE THAT WE WERE COUNTING TIME USING THE LUNAR CYCLE AT LEAST 34,000 YEARS AGO FROM CARVINGS ON BONES DISCOVERED IN AFRICA AND A SERIES OF CIRCLES AND CRESCENTS ETCHED INTO AN ANTLER FOUND IN EUROPE THAT ARE BELIEVED TO SHOW THE PHASES OF THE MOON.

PLAIT: THE THIRD ONE IS HOW LONG IT TAKES THE EARTH TO GO AROUND THE SUN, AND THAT'S A YEAR.

NARRATOR: USING THE SUN, WE ESTABLISHED A SOLAR YEAR OF 365 DAYS THAT ENCOMPASSED THE CHANGING SEASONS.

PLAIT: IF YOU SET UP A DISTANT LANDMARK AND LINE YOURSELF UP WITH THE SUN AT, SAY, THE MID-WINTER SOLSTICE, WHEN THE SUN CROSSES THE HORIZON BEHIND THERE, YOU MARK THAT DAY.

THEN, WHEN THE SUN CROSSES THE HORIZON THE NEXT DAY, IT'S A LITTLE BIT OFF AND A LITTLE BIT MORE AND A LITTLE BIT MORE DAY AFTER DAY.

THEN IT STARTS TO MOVE BACK OVER THE COURSE OF THE YEAR... AND RIGHT WHEN IT RISES BEHIND THAT LANDMARK AGAIN...BOOM!

YOU KNOW YOU'VE BEEN WAITING ONE YEAR.

NARRATOR: ALL OVER THE WORLD, SOME OF THE OLDEST MONUMENTS CREATED BY HUMAN HANDS WERE BUILT TO TRACK THE SOLAR YEAR.

THE EARLIEST EXAMPLES ARE MARKERS ON THE LANDSCAPE.

LIKE WURDI YOUANG, ERECTED BY ABORIGINAL PEOPLES IN AUSTRALIA UP TO 11,000 YEARS AGO.

A SERIES OF PITS DUG IN THE GROUND AT WARREN FIELD IN SCOTLAND, 10,000 YEARS AGO.

AND THE 7,000-YEAR-OLD STONE CIRCLE OF NABTA PLAYA IN EGYPT.

♪ OVER CENTURIES, THESE SIMPLE MARKERS COULD BECOME COLOSSAL STRUCTURES...

SOME OF WHICH HAVE SURVIVED TO THE PRESENT DAY.

STONEHENGE IS PERCHED AT THE TOP OF SALISBURY PLAIN IN THE SOUTH OF ENGLAND.

IT IS ONE OF THE MOST FAMOUS MONUMENTS ON THE PLANET.

BUILDING THIS MONUMENT 5,000 YEARS AGO WAS A HERCULEAN TASK.

THE LARGEST STONES AT STONEHENGE ARE UP TO 30 FEET LONG AND WEIGH UP TO 50 TONS.

SOME OF THEM WERE BROUGHT BY ANCIENT BRITONS FROM THE PRESELI HILLS IN WALES, 150 MILES AWAY.

CAMPION: NOBODY NEEDED TO TRANSPORT THOSE STONES.

THEY DID SO BECAUSE THOSE STONES HAD SOME VITAL QUALITY THAT WAS NEEDED AT STONEHENGE.

THESE ARE FANTASTICALLY COMPLEX EXERCISES.

NARRATOR: THE EFFORT REQUIRED TO BUILD STONEHENGE SHOWS JUST HOW IMPORTANT IT WAS.

PEOPLE WERE INVESTING VAST RESOURCES TO CREATE A CENTRALIZED GATHERING PLACE FOR THE ENTIRE ISLAND.

CAMPION: STONEHENGE WAS A FEAST SITE FOR POSSIBLY THE WHOLE OF BRITAIN.

PEOPLE WOULD KNOW A YEAR IN ADVANCE WHEN THE FEAST WAS GOING TO BE.

NARRATOR: BUT THIS WASN'T JUST A PLACE TO COME AND FEAST.

PEOPLE TRAVELED VAST DISTANCES TO CARRY OUT RITUAL ACTIVITIES HERE.

IT SEEMS THIS WAS A PLACE TO WORSHIP THE SUN.

CAMPION: THERE WOULD HAVE BEEN ALL SORTS OF RITUALS THERE TO ENCOURAGE THE POWER OF THE SUN TO RETURN LIFE TO THE LAND IN THE MIDDLE OF THE WINTER.

NARRATOR: STONEHENGE IS ALIGNED TO MARK SUNRISE ON THE SUMMER SOLSTICE AND SUNSET ON THE WINTER SOLSTICE.

A KIND OF GIANT SOLAR CALENDAR TO MARK THE LONGEST AND SHORTEST DAYS OF THE YEAR.

THIS CONNECTION BETWEEN RELIGION AND SOLAR ALIGNMENT CAN BE SEEN ACROSS THE WORLD.

♪ THE GREAT PYRAMID OF GIZA IS THE ONLY REMAINING WONDER OF THE ANCIENT WORLD.

IT IS LOCATED ON THE BANKS OF THE NILE IN EGYPT.

THE GREAT PYRAMID WAS BUILT OVER 4,500 YEARS AGO AS A TOMB FOR THE ANCIENT EGYPTIAN PHARAOH KHUFU.

IT IS THE CENTERPIECE OF A COMPLEX CONTAINING 3 GIANT PYRAMIDS.

AND THE PEOPLE WHO BUILT THESE PYRAMIDS TOOK GREAT CARE IN MAKING SURE THAT THEY WERE ALIGNED TO THE 4 CARDINAL POINTS.

MAN: WHEN WE LOOK AT THE PYRAMIDS TODAY, WE CAN SEE VERY CLEARLY THAT THEY ARE ALIGNED PRECISELY TOWARDS TRUE NORTH, SO, NORTH, EAST, SOUTH, AND WEST ARE ALMOST EXACTLY CORRECTLY REFERENCED.

NARRATOR: THE ANCIENT EGYPTIANS' CALCULATIONS WERE SO EXACT THAT THE PYRAMIDS ARE ALIGNED WITH THE POINTS OF THE COMPASS TO WITHIN 1/15TH OF A DEGREE.

THE FACT THAT THE ANCIENT EGYPTIANS TOOK SUCH PAINS TO ALIGN THE PYRAMIDS SO ACCURATELY SUGGESTS THERE MUST HAVE BEEN A GREATER MEANING.

PRICE: WE KNOW AT THE TIME OF THE GREAT PYRAMIDS THAT THERE IS AN INCREASED INTEREST IN THE SUN.

THAT'S MADE QUITE EXPLICIT IN THE TITLES OF THE PHARAOHS.

FOR THE FIRST TIME, THE PHARAOH IS DESCRIBED AS THE SON OF RA THE SUN GOD.

SO, IT'S INTERESTING THAT THE RELEVANCE OF SOLAR ALIGNMENT COULD BE TIED IN DIRECTLY TO THE IMPORTANCE OF THE KING AS THE CHILD OF THE SUN.

NARRATOR: IN THE WORLD OF ANCIENT EGYPTIAN RELIGION, THE SUN WAS EMBODIED BY THE GOD RA.

THE EGYPTIANS IMAGINED HIM IN A BOAT THAT HE SAILED ACROSS THE SKY EACH DAY.

AND THEY ALSO TOLD STORIES THAT EXPLAINED WHERE HE WENT WHEN THE SUN SET.

CAMPION: IN EGYPTIAN RELIGION, RA DIES EVERY NIGHT, AND HE GOES THROUGH A NOCTURNAL JOURNEY INTO THE UNDERWORLD.

ONE OF THE FUNCTIONS OF THE EGYPTIAN PRIESTHOOD WAS TO PREPARE FOR AND CELEBRATE THE REBIRTH OF RA THE SUN AT DAWN.

NARRATOR: RA'S IMPORTANCE TO THE ANCIENT EGYPTIANS CAN BE SEEN IN THE CELESTIAL ALIGNMENT OF THE PYRAMIDS OF GIZA.

BUT HOW DID BUILDERS ACHIEVE SUCH AN ASTONISHING LEVEL OF ACCURACY OVER 4,500 YEARS AGO?

IT'S EASY TO THINK THAT ANCIENT PEOPLE DIDN'T REALLY KNOW HOW TO DO ANY OF THE STUFF BUT, IN FACT, THEY UNDERSTOOD THE WAY THE SUN MOVED, THEY UNDERSTOOD THE WAY THE SHADOWS MOVED.

THEY HAD THE KNOWLEDGE OF ASTRONOMY AND GEOMETRY AND ENGINEERING THAT WAS FINE FOR DOING THIS SORT OF THING.

THEY WERE ABLE TO FIND THE DIRECTIONS OF NORTH, SOUTH, EAST, AND WEST PRETTY ACCURATELY.

AND ALL YOU NEED IS A LONG STICK, A PLUM BOB, AND A HAMMER.

THIS LONG STICK IS CALLED A GNOMON, AND IF YOU STICK IT IN THE GROUND STRAIGHT UP AND DOWN, IT WILL CAST A SHADOW DUE TO THE SUNLIGHT.

YEAH, THAT'S NOT BAD.

NOW THAT WE HAVE OUR GNOMON IN THE GROUND AND IT'S STRAIGHT UP AND DOWN, IT'S CASTING A SHADOW DUE TO SUNLIGHT.

NOW ALL WE HAVE TO DO IS MARK THE END OF THAT SHADOW SEVERAL TIMES OVER THE COURSE OF THE DAY.

THAT'S GOING TO MAKE AN ARC ON THE GROUND AS THE SUN RISES AND SETS, AND THAT'S WHAT'S GOING TO HELP ME FIND EAST AND WEST.

♪ ONCE WE HAVE THE ARC IN THE GROUND REPRESENTING THE LENGTH OF THE SHADOW OVER THE COURSE OF THE DAY, WE CAN TAKE A PIECE OF STRING AND TIE IT TO THIS GNOMON, MOVE OUT A CERTAIN DISTANCE, AND THEN JUST USE THAT TO DRAW A CIRCLE IN THE GROUND.

THAT CIRCLE WILL INTERSECT THE ARC IN TWO SPOTS, DRAW A LINE CONNECTING THOSE TWO POINTS.

THAT POINTS EAST AND WEST.

NARRATOR: EXPERTS BELIEVE THIS IS HOW THE ANCIENT EGYPTIANS USED THE SUN TO ALIGN THE PYRAMIDS OF GIZA TO NORTH, SOUTH, EAST, AND WEST.

♪ ACROSS THE WORLD, EVERY CIVILIZATION THAT WAS MOVED TO BUILD MAJOR RELIGIOUS MONUMENTS MADE THEM WITH CELESTIAL ALIGNMENTS.

MAN: THE AZTECS TENDED TO ORIENT THEIR MAIN TEMPLE TO THE EAST FACING WEST, ESPECIALLY FOR TENOCHTITLAN'S GREAT TEMPLE.

THE TWO SHRINES ON TOP OF IT WERE ALIGNED SO THAT ON THE EQUINOX, THE SUN WOULD RISE DIRECTLY BETWEEN THEM.

WE CAN SEE OTHER SIMILARLY ALIGNED MONUMENTS ON THAT EAST-WEST, NORTH-SOUTH MODEL IN INDIA... SOUTHEAST ASIA, IN CAMBODIA, THE GREAT TEMPLES OF ANGKOR, HUGE SITE.

♪ NARRATOR: THESE WERE CIVILIZATIONS SEPARATED BY THOUSANDS OF MILES AND CENTURIES IN TIME, THAT EVOLVED COMPLETELY INDEPENDENTLY OF ONE ANOTHER.

♪ AND YET, THEY WERE ALL USING ASTRONOMY TO BUILD CELESTIALLY ALIGNED MONUMENTS... TO NAVIGATE... AND EVEN TELL THE TIME.

BUT ASTRONOMY DIDN'T JUST INFLUENCE OUR ARCHITECTURE.

IT ALSO INSPIRED US TO CREATE TREASURES OF EXQUISITE BEAUTY.

AT THE HALLE STATE MUSEUM OF PREHISTORY IN EASTERN GERMANY, THERE'S AN ARTIFACT THAT COULD BE OUR EARLIEST ASTRONOMICAL INSTRUMENT.

IT IS KNOWN AS THE NEBRA SKY DISC.

DISCOVERED IN 1999, IT IS BELIEVED TO HAVE BEEN MADE OVER 3,500 YEARS AGO IN THE HEART OF BRONZE AGE EUROPE.

MADE FROM BRONZE OVERLAID WITH GOLD, THE DISC HAS BEEN INTERPRETED TO SHOW A VARIETY OF OBJECTS IN THE NIGHT SKY.

IT NOW SITS PERMANENTLY BEHIND GLASS.

BUT DR. HARALD MELLER HAS USED THIS PRECIOUS, PERFECT COPY TO STUDY ITS SECRETS.

[MELLER SPEAKING GERMAN] NARRATOR: BY LINING UP THESE HORIZON ARCS WITH THE SUNRISE ON SPECIFIC DAYS OF THE YEAR, IT COULD BE USED AS A KIND OF SOLAR CALENDAR.

[SPEAKING GERMAN] NARRATOR: THE NEBRA SKY DISC SHOWS HOW A CULTURE WITHOUT WRITING COULD USE PICTURES TO RECORD ASTRONOMICAL OBSERVATIONS.

BUT 2,000 MILES AWAY, ONE OF OUR GREATEST CIVILIZATIONS WOULD USE THE WRITTEN WORD TO TAKE ASTRONOMY TO A WHOLE NEW LEVEL.

IT ALL BEGAN IN A PLACE OFTEN REFERRED TO AS THE CRADLE OF CIVILIZATION...

ANCIENT MESOPOTAMIA.

♪ WHEN WE TALK ABOUT ANCIENT MESOPOTAMIA, WE ARE REFERRING TO A GEOGRAPHICAL REGION THAT IS CURRENTLY COVERED BY IRAQ, SYRIA, AND PARTS OF TURKEY.

IT'S THE REGION THAT IS AROUND THE TIGRIS AND EUPHRATES RIVERS.

AND THAT'S ACTUALLY WHERE THE NAME COMES FROM.

MESOPOTAMIA IS GREEK FOR "THE LAND BETWEEN RIVERS."

NARRATOR: WITHIN THE REGION OF ANCIENT MESOPOTAMIA WAS THE FAMOUS CITY OF BABYLON.

IT WAS THE BABYLONIANS WHO GAVE US OUR EARLIEST KNOWN SCIENTIFIC OBSERVATIONS OF THE SKIES, STARTING OVER 3,000 YEARS AGO.

THEY WERE THE FIRST TO SYSTEMATICALLY RECORD OBSERVATIONS ABOUT THE PLANETS AND THE STARS, ABOUT THE MOTION OF CELESTIAL BODIES, AND TO TRY TO CORRELATE THEM TO MORE FAMILIAR EVENTS THAT HAPPENED IN THE HUMAN SPHERE.

NARRATOR: MANY OF THESE RECORDINGS HAVE SURVIVED TO THIS DAY.

THEY ARE KEPT HERE, AT THE BRITISH MUSEUM IN LONDON.

♪ THEY ARE WRITTEN IN CUNEIFORM, AN ANCIENT FORM OF WRITING THAT DOMINATED IN THIS PART OF THE WORLD FOR CENTURIES.

♪ MAN: CUNEIFORM IS A SYSTEM OF WRITING PREDOMINANTLY ON CLAY USING A WEDGE-SHAPED STYLUS TO PRODUCE WEDGE-SHAPED SIGNS, AND THESE SIGNS CAN MAKE UP WORDS.

NARRATOR: HUNDREDS OF THOUSANDS OF CUNEIFORM TEXTS HAVE BEEN FOUND BY ARCHAEOLOGISTS.

BUT THE KNOWLEDGE TO DECODE THEM IS RELATIVELY RECENT.

EVEN TODAY, THERE ARE VERY FEW PEOPLE IN THE WORLD WHO CAN READ THEM.

PROFESSOR JOHN STEELE IS ONE OF THESE FEW.

STEELE: THE BABYLONIANS WERE THE FIRST TO REALLY GET INTERESTED IN MAKING DETAILED, PRECISE, AND REGULAR OBSERVATIONS.

THEY WERE LOOKING FOR ECLIPSES.

THEY WERE LOOKING FOR THE MOTION OF THE MOON PAST STARS, THE MOTION OF THE PLANETS PAST STARS.

THIS A VERY INTERESTING COLLECTION OF LUNAR ECLIPSE OBSERVATIONS.

THE COMPILATION EXTENDS FOR OVER 400 YEARS FROM THE MIDDLE OF THE EIGHTH CENTURY DOWN TO JUST BEFORE 300 B.C., AND YOU CAN SEE HERE IT'S DIVIDED UP INTO A GRID LIKE A TABLE, LIKE A MODERN SPREADSHEET, AND WITHIN EACH CELL OF THE TABLE, WE HAVE A REPORT OF A LUNAR ECLIPSE.

NARRATOR: THESE RECORDS WERE ADDED TO FROM GENERATION TO GENERATION...

ENABLING BABYLONIAN ASTRONOMERS TO LOOK AT PATTERNS AND CYCLES IN THE SKIES OVER CENTURIES.

STEELE: AS A CONSEQUENCE OF THAT, THEY WERE THE FIRST PEOPLE TO ATTEMPT TO ANALYZE THESE THINGS MATHEMATICALLY, TO MAKE PRECISE AND DETAILED AND ACCURATE PREDICTIONS.

NARRATOR: CONTAINED IN THESE TABLETS IS THE VERY BIRTH OF MODERN ASTRONOMY.

STEELE: SO, REALLY, ON BOTH THE OBSERVATIONAL AND THE PREDICTIVE OR THEORETICAL SIDE, BABYLON IS WHERE IT ALL STARTS ACROSS THE WORLD.

NARRATOR: THE BABYLONIANS BELIEVED THAT BY USING ASTRONOMY TO UNDERSTAND THE SKIES, THEY COULD INTERPRET THE DESIRES OF THE GODS.

AL-RASHID: THE CELESTIAL BODIES, WHETHER THEY WERE STARS OR PLANETS, WERE THOUGHT TO BE THE WRITING OF THE GODS, AND THE SKY WAS UNDERSTOOD AS A KIND OF STONE TABLET ON WHICH THE GODS INSCRIBED THEIR MESSAGES.

NARRATOR: IF THEY COULD READ THESE DIVINE MESSAGES, THE BABYLONIANS COULD TAKE APPROPRIATE ACTION IN THE MORTAL REALM.

AL-RASHID: AN ECLIPSE, FOR EXAMPLE, WAS A VERY DANGEROUS PHENOMENON THAT REQUIRED THE KING TO BE HIDDEN AWAY AND A SUBSTITUTE PUT IN HIS PLACE FOR A FEW MONTHS UNTIL THE DANGER WAS PERCEIVED TO HAVE PASSED.

NARRATOR: THIS NEED TO LOOK TO THE SKIES FOR HELP IN MAKING IMPORTANT DECISIONS CAN BE SEEN ALL OVER THE WORLD.

♪ IN CENTRAL AMERICA, ANOTHER OF OUR GREAT CIVILIZATIONS BECAME SKILLED ASTRONOMERS TO BETTER UNDERSTAND THE WILL OF THE GODS.

CARBALLO: WE CAN PICK UP TRACES OF MAYA CULTURE GOING BACK TO THE SECOND MILLENNIUM BCE.

THE MAYAS CREATED THE MOST SOPHISTICATED WRITING SYSTEM OF THE PRE-COLUMBIAN AMERICAS.

THEY WROTE ON THEIR POTTERY.

THEY WROTE IN SCULPTED HIEROGLYPHS ON MONUMENTS AND ON STAIRWAYS.

NARRATOR: THESE INSCRIPTIONS SURVIVE ON MAYAN DOCUMENTS ACROSS PARTS OF MODERN-DAY MEXICO, GUATEMALA, BELIZE, AND HONDURAS.

WE ALSO HAVE RECORDS THAT THE MAYA WROTE BOOKS ON A PAPER MADE FROM THE FICUS TREE.

ALMOST ALL OF THESE HAVE BEEN LOST OVER TIME, WHETHER THEY DECOMPOSED IN THE HUMID CENTRAL AMERICAN CLIMATE OR WERE DESTROYED BY MARAUDING SPANISH CONQUISTADORS IN THE 16TH CENTURY.

BUT AT THE SAXON STATE LIBRARY IN EASTERN GERMANY, LOCKED AWAY IN A ROOM KNOWN AS THE TREASURE CHAMBER, IS ONE OF ONLY 4 MAYAN BOOKS LEFT IN THE WORLD.

IT IS KNOWN AS THE DRESDEN CODEX.

AND ARCHAEOLOGIST DR. CHRISTIAN PRAGER HAS STUDIED IT FOR YEARS.

PRAGER: THIS BOOK HERE COMES FROM THE 12TH OR 13TH CENTURY, BUT WAS USED UNTIL THE ARRIVAL OF THE SPANIARDS.

NARRATOR: THE DRESDEN CODEX IS THE MOST COMPLETE OF THE 4 SURVIVING BOOKS WRITTEN BY THE MAYA.

IT SHOWS HOW THE MAYANS USED THE SKIES TO INFLUENCE DECISION-MAKING IN THEIR EVERYDAY LIVES.

PRAGER: THE DRESDEN CODEX WAS A BOOK THAT WAS USED BY MAYA PRIESTS TO GIVE ADVICE TO PEOPLE.

FOR EXAMPLE, WHICH IS THE BEST DAY TO GIVE FOOD TO A SPECIFIC GOD OR WHEN IS THE BEST DAY TO GO TO HUNT AND ON WHICH DAY WILL THERE BE RAIN AND SO ON.

NARRATOR: THE CODEX CONTAINS A NUMBER OF SECTIONS WHICH RELATE DIRECTLY TO THE SKIES AND THEIR RELIGIOUS SIGNIFICANCE.

PRAGER: THEY BELIEVED IN A LOT OF GODS.

AND THEY HAD SPECIFIC GODS FOR THE RAIN, FOR THE ROYAL POWER, FOR DEATH, AND SO ON.

THE MOON GODDESS IS THE SEATED LADY HERE WITH THE BLACK HAIR, WITH A FIGURE ON HER BACK.

♪ THIS IS A DEPICTION OF A SUN ECLIPSE.

IT ALWAYS HAS A BLACK AND WHITE AREA.

AND THE SUN ECLIPSE IS HANGING FROM A CELESTIAL BAND.

NARRATOR: AS WELL AS PROVIDING RITUAL AND RELIGIOUS INFORMATION, IT ALSO GIVES US A CLEAR WINDOW INTO THE WORLD OF MAYAN ASTRONOMY.

PRAGER: THE ASTRONOMICAL OBSERVATIONS IN THE DRESDEN CODEX ARE VERY EXACT.

THEY CAN BE COMPARED TO OUR KNOWLEDGE FROM TODAY.

NARRATOR: JUST LIKE THE BABYLONIANS, THE MAYA COMPILED TABLES OF COMPLEX ASTRONOMICAL OBSERVATIONS.

PRAGER: THE ASTRONOMICAL INFORMATION THAT WE HAVE IN THE DRESDEN CODEX ARE MAINLY ON VENUS CYCLES AND THE ECLIPSE CYCLES, THE ECLIPSE--LUNAR AND SOLAR ECLIPSE.

THIS IS THE MOST IMPORTANT THING.

NARRATOR: VENUS WAS PARTICULARLY IMPORTANT TO THE MAYANS.

ITS PRESENCE IN THE SKY HAD THE POSSIBILITY TO PREDICT WARFARE.

AND BY WATCHING VENUS CLOSELY, THE MAYANS WERE ABLE TO MAKE A DISCOVERY ABOUT IT THAT ELUDED OTHER CIVILIZATIONS.

ONE OF THE FASCINATING THINGS ABOUT MESOAMERICAN ASTRONOMERS IS THAT THEY FIGURED OUT THAT VENUS WAS A SINGLE ENTITY.

WHEREAS IN MUCH OF THE WORLD, PEOPLE THOUGHT THAT IT WAS AN EVENING STAR AND A MORNING STAR AND THEY WERE TWO SEPARATE BEINGS, BUT MESOAMERICANS FIGURED OUT THAT THERE WAS A CYCLE WHERE IT RETURNS TO THE SAME SPOT ON THE LANDSCAPE.

NARRATOR: THE CALCULATIONS FOR THE VENUS CYCLES CAN BE SEEN HERE IN THE DOTS AND BARS THAT THE MAYANS USED TO SIGNIFY NUMBERS.

PRAGER: THEY CALCULATED THE CORRECT DAY WHEN THERE WAS THE VENUS AS MORNING STAR, WHEN THERE WAS THE VENUS AS EVENING STAR.

THE PHASE OF THE VENUS IS 583 POINT SOMETHING DAYS AND THEY CALCULATED 584 DAYS.

SO, AFTER 13 YEARS, THERE IS A DEVIATION OF ONE DAY.

THEY CORRECTED THIS ONE DAY.

SO, ACCORDING TO THE KNOWLEDGE THAT WE HAVE TODAY, THESE PREDICTIONS OF THE VENUS POSITIONS WERE VERY EXACT.

NARRATOR: ALL OVER THE WORLD, OUR GREAT CIVILIZATIONS LOOKED AT THE SKIES AND RECORDED THE THINGS THEY SAW.

THE EGYPTIANS BEGAN TO DRAW UP STAR CLOCKS TO TRACK THE MOTIONS OF SELECTED STARS.

ANCIENT INDIAN STARGAZERS WROTE TEXTS DETAILING THEIR OBSERVATIONS OF THE SKIES.

AND CHINESE ASTRONOMERS CREATED COMPLEX MAPS OF THE STARS.

THE SCIENCE OF ASTRONOMY HAD ARRIVED.

♪ ALL ANCIENT ASTRONOMERS NEEDED WAYS TO NAVIGATE THE FANTASTICALLY COMPLEX NIGHT SKY.

PLAIT: YOU GO OUT AT NIGHT AND YOU LOOK UP IN THE SKY AND YOU SEE THE STARS, AND THOSE STARS STAY IN THAT SAME FIXED PATTERN NIGHT AFTER NIGHT AFTER NIGHT.

NARRATOR: THOSE PATTERNS GAVE OUR ANCIENT ANCESTORS A WAY TO CREATE MEMORABLE LANDMARKS IN THE SKY.

TODAY, WE KNOW THEM AS CONSTELLATIONS.

PLAIT: A CONSTELLATION IS A GROUP OF STARS, THAT'S WHAT THE WORD MEANS, AND SO, WE TEND TO SEE THE STARS IN THESE PATTERNS WHEN WE LOOK ACROSS THE SKY.

FOR EXAMPLE, THERE'S URSA MAJOR, THE BIG BEAR.

OR ORION THE HUNTER, WHICH LOOKS ENOUGH LIKE A PERSON WITH THEIR ARMS RAISED.

LEO THE LION KIND OF LOOKS LIKE A LION SEEN FROM THE SIDE, AND SO, A LOT OF DIFFERENT CULTURES RECOGNIZE THAT IF THEY'RE FAMILIAR WITH LIONS.

NARRATOR: BUT NOT EVERY CULTURE SAW THE SAME SHAPES IN THE STARS.

WOMAN: CONSTELLATIONS HAVE MORE TO DO WITH PATTERNS THAT HAVE HAD CULTURAL OR OTHER TYPES OF SIGNIFICANCE FOR THE VARIOUS CULTURES AND CIVILIZATIONS WHO HAVE NOTICED THESE PATTERNS THROUGHOUT HUMAN HISTORY.

NARRATOR: CHINESE ASTRONOMERS SAW A MONKEY, A SNAKE, AND A DRAGON.

NATIVE AMERICANS SAW A BEAVER, AN OWL, AND A WOLF.

AND THE AZTECS SAW PRACTICAL THINGS FROM THEIR EVERYDAY LIVES.

CARBALLO: WHAT WE CALL THE PLEIADES, THE AZTECS CALLED TIANQUIZTLI, WHICH IS THE MARKETPLACE.

THEN, WHAT WE CALL ORION'S BELT AND SWORD WAS SEEN AS A FIRE DRILL.

NARRATOR: TODAY IN THE WESTERN WORLD, THERE ARE 88 OFFICIALLY RECOGNIZED CONSTELLATIONS IN THE NIGHT SKY.

BUT MOST OF US ARE FAMILIAR WITH A MUCH SMALLER NUMBER OF THEM.

THEY ARE THE ONES THAT HAVE BEEN GROUPED TOGETHER INTO WHAT WE NOW CALL THE ZODIAC.

PLAIT: WE RECOGNIZE 12 OFFICIAL ZODIAC CONSTELLATIONS.

THE ONES YOU'VE HEARD OF-- LIBRA, TAURUS, GEMINI, AND ALL OF THOSE.

NARRATOR: THERE IS ARIES, THE RAM... VIRGO, THE MAIDEN... AND CANCER, THE CRAB.

THE ZODIAC WAS ESTABLISHED BY BABYLONIAN ASTRONOMERS AROUND 2,500 YEARS AGO... AND IT'S THE SAME ZODIAC THAT EXISTS TO THIS DAY.

BUT PICKING 12 CONSTELLATIONS FROM THE COUNTLESS PATTERNS IN THE SKY WASN'T JUST A FLIGHT OF FANCY.

THERE WAS A SERIOUS SCIENTIFIC REASON BEHIND IT.

PLAIT: AS THE EARTH GOES AROUND THE SUN OVER THE COURSE OF THE YEAR, IT APPEARS THAT THE SUN IS MOVING IN A LINE AROUND THE SKY.

WE CALL THAT LINE THE ECLIPTIC.

AND THE CONSTELLATIONS THAT IT PASSES THROUGH, THOSE ARE THE ZODIAC CONSTELLATIONS.

NARRATOR: THE 12 ZODIAC CONSTELLATIONS PROVIDED BABYLONIAN ASTRONOMERS WITH A VIRTUAL GRID SYSTEM IN THE SKY.

THEY USED THIS GRID TO ACCURATELY IDENTIFY THE LOCATIONS OF ALL THEIR OBSERVATIONS.

THIS ENABLED THE BABYLONIANS TO TAKE THE SCIENCE OF ASTRONOMY TO A WHOLE NEW LEVEL.

AL-RASHID: WHAT THE ZODIAC DID WAS IT ALLOWED THEM TO ORGANIZE INFORMATION IN A NEW WAY.

FROM ABOUT THE SIXTH AND FIFTH CENTURIES B.C.

ONWARD, WE START TO REALLY SEE ADVANCED MATHEMATICAL ASTRONOMY BEING CARRIED OUT BY SCHOLARS, ASTRONOMERS, AND ASTROLOGERS IN ANCIENT BABYLONIA.

NARRATOR: THEY WERE ABLE TO BUILD A MATHEMATICAL MODEL OF THE COSMOS AND TO PREDICT THE MOVEMENTS OF STARS AND PLANETS.

BUT WHILE THEIR ASTRONOMY WAS SCIENTIFIC, THEIR WRITINGS SHOW THAT THEY STILL BELIEVED THAT EVERYTHING IN THE SKIES WAS MOVED BY GODS AND GODDESSES.

AL-RASHID: THE SORT OF SYSTEMATIC OBSERVATION AND EXTRAPOLATION THAT WE FIND IN THESE TEXTS IS A KIND OF TESTAMENT TO THE ASSUMPTION THAT THE GODS WERE RESPONSIBLE FOR WHAT WE SAW IN THE SKY AND THAT THE DIVINE WAS INSEPARABLE FROM THE NATURAL SPHERE.

NARRATOR: BUT THE RISE OF A NEW CIVILIZATION WAS ABOUT TO COMPLETELY REVOLUTIONIZE THE WAY WE UNDERSTOOD THE COSMOS.

♪ ALMOST 3,000 YEARS AGO, THE PEOPLES OF GREECE AND THE AEGEAN SEA WERE EMERGING FROM A DARK AGE.

♪ FOR THE ANCIENT GREEKS, THE WORLD WAS A PLACE THEY SHARED WITH SUPERNATURAL BEINGS... WHERE A GOD COULD TURN A MORTAL FAVORITE INTO A CONSTELLATION OF STARS... AND THE SUN WAS DRIVEN ACROSS THE SKY EACH DAY IN A FIERY CHARIOT.

CAMPION: IT WAS CLEARLY THE CUSTOM TO EXPLAIN THE MOVEMENTS OF THE STARS AND PLANETS THROUGH STORIES ABOUT GODS AND GODDESSES.

NARRATOR: THESE DIVINE BEINGS POPULATE THE GREAT EPIC POEMS OF EARLY ANCIENT GREECE.

LIKE OTHER ANCIENT PEOPLE, THE GREEKS DIDN'T REGARD THE HEAVENS AS EXISTING IN SOME OTHER DIMENSION.

THEIR STORIES TELL OF A SHARED WORLD IN WHICH GODS AND MORTALS LIVE ALONGSIDE EACH OTHER.

YET ONLY THE GODS COULD FREELY PLUNGE INTO THE DEPTHS OF THE OCEAN, OR MAKE THEIR HOME ON THE HIGHEST MOUNTAIN.

TO HUMANS, THE HEAVENS WERE OUT OF BOUNDS.

ANY MORTAL TRYING TO REACH THE SKIES WAS IN DANGER OF INCURRING DIVINE ANGER-- AND CERTAIN DOWNFALL.

AND PERHAPS NO GREEK MYTH IS A BETTER EXAMPLE OF THIS IDEA THAN THE STORY OF A MAN CALLED DAEDALUS AND HIS SON... ICARUS.

WOMAN: DAEDALUS FLEW AHEAD, LIKE A BIRD.

HE URGED THE BOY TO FOLLOW, AND SHOWED HIM THE DANGEROUS ART OF FLYING.

♪ THE BOY BEGAN TO DELIGHT IN HIS DARING FLIGHT AND, DRAWN BY DESIRE FOR THE HEAVENS, SOARED HIGHER.

♪ HIS NEARNESS TO THE SUN SOFTENED THE WAX THAT HELD THE WINGS, AND THE WAX MELTED.

HE FLAILED WITH BARE ARMS, BUT COULD NOT RIDE THE AIR.

EVEN AS HIS MOUTH CRIED HIS FATHER'S NAME, IT VANISHED INTO THE DARK BLUE SEA.

♪ NARRATOR: IT WOULD BE MORE THAN 2,000 YEARS BEFORE MAN RISKED THE WRATH OF THE GODS AND AGAIN TOOK TO THE SKIES.

BUT EVEN AS ICARUS' FABLED FEATHERS TOUCHED THE WATER, THE ANCIENT GREEKS HAD ALREADY SET SAIL TO TRADE, AND COLONIZE LANDS FAR BEYOND THEIR OWN.

SKILLED SAILORS, THEY VENTURED OVERSEAS IN SEARCH OF NEW OPPORTUNITY.

AS THEY DID SO, THEY INCREASINGLY CAME INTO CONTACT WITH OTHER CULTURES.

THEY TOOK THE ALPHABET FROM THE PHOENICIANS.

♪ THEY TOOK ARTISTIC INFLUENCES FROM THE EGYPTIANS.

AND FROM THE BABYLONIANS, THEY TOOK ASTRONOMY.

THE BABYLONIAN ASTRONOMY IS A REALLY STRONG CURRENT THAT FLOWS INTO THE GREEK ARCHAIC CULTURE.

THERE'S THE PLANETARY TABLES-- THE RECORDING OF PLANETARY OBSERVATIONS THAT INFLUENCE REALLY STRONGLY THE WAY THAT GREEKS UNDERSTAND ASTRONOMY AND DO ASTRONOMY.

NARRATOR: ARMED WITH ASTRONOMICAL KNOWLEDGE FROM THE BABYLONIANS, THE GREEKS BEGAN TO REINTERPRET THE WAY THEY VIEWED THE COSMOS.

THEY WEREN'T JUST SATISFIED WITH OBSERVATION AND PREDICTION.

THEY WANTED TO KNOW WHY THE THINGS THEY SAW IN THE SKY MOVED THE WAY THEY DID.

ONE MAN IS OFTEN CREDITED WITH BEING THE PERSON TO PROVIDE THE BIGGEST CHANGE IN OUR UNDERSTANDING OF THE COSMOS.

HIS NAME WAS THALES.

HAYTON: THALES OF MILETUS IS THE PERSON WE TEND TO CALL THE FATHER OF PHILOSOPHY.

HE SHIFTS THE WAY IN WHICH GREEKS THINK ABOUT ASKING QUESTIONS ABOUT THE NATURAL WORLD.

NARRATOR: THALES LIVED IN THE SIXTH CENTURY B.C.

HE WAS FROM MILETUS, A GREEK SETTLEMENT ON THE SHORES OF MODERN TURKEY, THAT HAD DIRECT ACCESS TO THE IDEAS AND KNOWLEDGE OF THE EAST.

HE IS CREDITED WITH BEING THE FIRST PERSON TO QUESTION THE BELIEF THAT THE COSMOS COULD BE EXPLAINED THROUGH MYTHOLOGY.

FOR THALES AND HIS FELLOW PHILOSOPHERS, EVERY OBSERVABLE THING IN THE COSMOS HAD TO HAVE A RATIONAL, SCIENTIFIC EXPLANATION.

THEY BELIEVED THIS WAS AS TRUE FOR THINGS IN THE SKIES, LIKE THE MOVEMENTS OF THE SUN AND THE MOON, AS IT WAS FOR THINGS THAT HAPPENED ON EARTH.

[THUNDER] HAYTON: HE STOPS ASKING QUESTIONS ABOUT INDIVIDUAL PHENOMENON-- THIS EARTHQUAKE, THAT STORM, THIS LIGHTNING BOLT-- [THUNDER] AND INSTEAD ASKS QUESTIONS ABOUT PHENOMENON: EARTHQUAKES, LIGHTNING BOLTS, STORMS.

IN THE PROCESS, THESE PHENOMENA CEASE TO BE SUPERNATURAL OR LINKED TO SUPERNATURAL GODS AND INSTEAD BECOME NATURAL.

IT'S SOMETHING THAT HAPPENS NATURALLY.

NARRATOR: THIS WAS A PIVOTAL MOMENT IN OUR SCIENTIFIC UNDERSTANDING OF THE UNIVERSE.

IT WAS NOW POSSIBLE TO BELIEVE THAT EVERYTHING WE OBSERVED IN THE SKIES WAS PART OF THE NATURAL, NOT THE SUPERNATURAL WORLD.

HAYTON: WHAT'S AMAZING IS WE HAVE SUCH AN INCREDIBLE SHIFT FROM THE DARK AGES TO THIS PERIOD WHEN WE HAVE THE BIRTH OF PHILOSOPHY, THE BIRTH OF SCIENCE.

NARRATOR: THIS WAS THE DAWN OF A NEW ERA IN HUMAN HISTORY... WHERE WE WOULD CHANGE THE WAY WE VIEW THE WORLD AROUND US, THE SKIES ABOVE, AND EVERYTHING IN THEM...

FOREVER.

♪ OUR EARTH UNDERGOES AN EPIC TRANSFORMATION.

PLAIT: THE QUESTION ISN'T "IS THE EARTH ROUND?"

THE QUESTION REALLY IS "HOW BIG IS IT?"

NARRATOR: WE ESTABLISH A MECHANICAL MODEL OF THE UNIVERSE.

MAN: PTOLEMY SEES THE EARTH AT THE CENTER, AND THEN IT'S SURROUNDED BY A SERIES OF CRYSTALLINE SPHERES.

NARRATOR: AND WE CALL INTO QUESTION OUR PLACE AT THE CENTER OF IT ALL.

WOMAN: HUMANITY LOSES ITS POSITION OF CENTRALITY, SO, PHILOSOPHICALLY AND POTENTIALLY THEOLOGICALLY, THIS IS QUITE RADICAL.

♪ ANNOUNCER: TO ORDER THIS PROGRAM ON DVD, VISIT SHOP PBS OR CALL 1-800-PLAY-PBS.

ALSO AVAILABLE ON AMAZON PRIME VIDEO.

♪