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The story of the Sun starts 13 billion years ago
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with the Big Bang.
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[loud explosion]
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In an instant, the universe was born.
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And since then, it's been expanding
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at the speed of light.
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Within the universe, there are 100 billion galaxies.
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Our galaxy is but one of them.
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In it, there are 100 billion stars.
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And towards the outer edge of one of the spiral arms
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is an almost insignificant dot:
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a medium-sized, not very bright, undistinguished star.
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Up close, it's a different story.
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On the planets closest to the Sun,
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Mercury and Venus, the heat is intense.
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Their surface is scorched.
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Further out through the solar system,
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the Sun's rays weaken
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until they are powerless against the chill of space.
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The outer planets are frozen,
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but in the middle lies the Goldilocks planet:
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not too hot and not too cold.
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In fact, it's just right.
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And life has flourished in the warm glow.
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All life on Earth owes its existence to the Sun.
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It powers every natural system
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and sustains every plant and animal.
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Without the Sun, the planet would be a barren,
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lifeless ball of rock.
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Recognizing that power,
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humans have always worshipped the Sun,
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but we have also always striven to understand it.
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These monuments are more than just temples.
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They are calendars and observatories,
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tools for studying the Sun.
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And some of them are still operational.
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This is Orkney.
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To live here is to know the importance
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of the Sun.
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In the summer, the days are long
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and full of light.
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In December, it's a different story.
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(Richards) It's midwinter.
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It's about 11:00 in the morning,
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and it's still not light completely.
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There's a strong wind coming in off the Atlantic,
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and it's cold, and it's wet.
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And that's pretty much typical
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of this time of the year up here.
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(narrator) Yet despite the cold, in the Stone Age,
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5,000 years ago, a civilization thrived here.
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The island is covered in the remains of their society.
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The ruins are full of mystery.
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We know little about the people who lived here.
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But they did leave evidence of the important role
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the Sun played in their lives.
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Maeshowe, 1,000 years older than the pyramids,
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is one of the finest examples of Stone Age architecture.
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While entering Maeshowe, I have to crouch right down
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and then confronted with a passage
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which seems to actually go on and on and on.
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Slightly feeling the impression of going uphill, upslope.
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I'm coming through, clearly, another doorway.
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Suddenly, the whole thing opens out
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into the most amazing chamber.
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This alone is probably the highest and largest
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enclosed space that neolithic Orcadians
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would have experienced.
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When it was excavated, when it was first entered
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back in the 19th century,
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the clay floor was littered
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with broken pieces of human skull.
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This is a place of the dead.
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This is a house of the dead.
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(narrator) Most of the time,
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the occupants of the tomb were left in complete darkness.
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Then, at sunset on the winter solstice,
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the shortest day of the year, something amazing happens.
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The light of the setting Sun
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shines straight up the entrance tunnel
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and illuminates the interior.
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(Richards) Well, the significance is that
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it's marking the shortest time of the year
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with the least light, and from that point on,
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slowly and gradually, the light is going to increase;
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the days are going to grow longer.
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So what's happening here is that the dead,
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the ancestors, are being awoken on that shortest day.
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(narrator) The winter solstice events at Maeshowe
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demonstrate an intimate and precise knowledge
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of the Sun's movements through the sky.
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It was the first step on our journey
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to understand the Sun and its many effects on us.
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To complete that journey,
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we've had to travel to the furthest depths of space
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and to the heart of the smallest atom.
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And with every closer look, the Sun has always surprised us.
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To our ancestors, its power was its reliability:
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always on time, never changing.
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But the reality is proving to be very different.
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(Mason) Most people think of the Sun as quite a boring,
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constant sort of thing. (Mason) Most people think of the Sun as quite a boring,
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constant sort of thing.
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But in fact, it's not at all.
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It's changing all the time, and if you look,
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you can see those changes in a matter of minutes or hours,
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and it's far from static and boring.
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It's changing, and it's got a life of its own.
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(narrator) Modern solar observatories
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magnify and filter the Sun's light
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to get past the constant glare and give a clear view
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of the surface.
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This is the actual face of the Sun.
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It is turbulent and boiling.
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Never the same from one second to the next,
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the surface bubbles like a giant bowl of porridge.
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Each bubble is 1,000 miles across.
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The heat and light brought to the surface
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raises its temperature to 6,000 degrees centigrade,
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enough to vaporize solid rock.
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And the Sun is huge.
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You could fit the Earth inside it a million times over.
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Periodically, huge explosions rip through the surface,
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releasing the energy of a billion atomic bombs
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in seconds.
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All this is on the surface.
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To understand the Sun,
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we must know what is going on deep inside.
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That is where the power is generated.
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So for centuries,
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scientists have been devising ways
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to probe the heart of the Sun.
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Some of them have been complex
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and some of them very simple.
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And the first step
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is to figure out just how powerful the Sun is.
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(Alexander) It's easy to appreciate the power of the Sun on a nice
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hot summer's day, like here on the Texas Gulf Coast.
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And you can feel the power of the Sun on your skin.
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Sunscreen's on.
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But man, the Sun is just, you know, the actual physics
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of what's going on inside the Sun,
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the power that the Sun, the energy that the Sun
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is releasing, is almost beyond comprehension.
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(narrator) But it is only almost beyond comprehension.
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And you can measure its power output
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with some simple apparatus.
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(Alexander) One of the earliest experiments to try and measure
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the actual power of the Sun was by astronomer William Herschel
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in the 19th century,
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when he had the brilliant idea of just watching
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a piece of ice melt to see
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how long it would take, and therefore,
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from the properties of the ice,
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work out how much sunlight was coming to the ground.
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[beeping noise] work out how much sunlight was coming to the ground.
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(narrator) As a demonstration of the Sun's power,
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it doesn't look that impressive,
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but Herschel realized that he could
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use the time it takes to melt one bit of ice
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to calculate the Sun's total power output.
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(Alexander) So here we see the ice is almost completely melted.
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Roughly 29 minutes, almost half an hour.
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But Herschel was able
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to use this experiment and the time that it took
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to melt the ice to work out
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some basic properties of the Sun.
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(narrator) Here's how Herschel's thinking worked.
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In the time it takes to melt a slab of ice on Earth,
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the Sun is radiating heat in all directions,
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enough to melt a complete shell of ice around it,
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a diameter of 300 million kilometers.
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A shell 1/2 a centimeter thick and 300 million kilometers
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across contains a lot of ice,
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enough to make an ice cube bigger than the Earth.
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To melt that much ice in just 30 minutes
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would take an energy input
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of a billion billion billion watts.
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It's a rough but surprisingly accurate experiment.
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Modern satellite readings confirm the figures
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to within a few percent.
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It's an almost unimaginable amount of energy.
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If we could harness the Sun's power output
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for a single second,
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it would satisfy the world's energy demands
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for the next million years.
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But it's one thing to know how much power
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the Sun is producing.
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It's something else to know how it's doing it.
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Until the middle of the 20th century,
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no one had any idea what made the Sun work.
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For scientists in Herschel's time,
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it was a mystery.
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(Alexander) One of the issues was, of course,
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what powered the Sun?
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And some very clever people actually considered the fact
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that the Sun might be powered by burning coal.
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I mean, it seems ludicrous, but why not coal?
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That was an important source of energy on the Earth
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at that part of the 19th century.
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(narrator) If the Sun was made entirely of coal,
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there would be one unfortunate consequence.
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It would burn itself out in just a few thousand years.
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Today that sounds ridiculous.
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But 200 years ago, it didn't seem so unlikely.
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It was widely believed that the Earth
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was only a few thousand years old.
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But in the mid-19th century,
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a new science was emerging that was painting
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a very different picture of the age of the Earth.
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By looking at the deepest layers of rocks,
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geologists were discovering that the Earth was much older
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than anyone had previously imagined.
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If that was true, then the Sun
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also had to have been burning for much, much longer.
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(Hathaway) You can see the strata in the lines
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in the rock in back of you that represent hundreds
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of million years of geological history.
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The top of Sacramento Peak up beyond this,
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we find fossils that are 300 million years old.
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Below Sacramento Peak, we've got more than a kilometer
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of these strata that are far older than that.
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From the age of these strata, geologists knew that the Earth
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was at least a billion years old.
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At the same time,
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astronomers thought that the Sun was only 10,000 years old.
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If the geologists were right,
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then astronomers had to find some other source
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for the Sun producing its energy.
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(narrator) The search for the source of energy
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that could power the Sun for billions of years
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lasted for nearly a century.
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Eventually, scientists would find the answer in the forces
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that hold atoms together
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and in the nature of matter itself.
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But first, you have to know what the Sun is made of.
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To find that out,
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you need to take a very close look at sunlight.
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(Hathaway) When you take the light from the Sun
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and pass it through a prism-- spread it out into the colors--
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as you look through it,
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you notice that it isn't uniform,
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that there are places that are darker.
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Each of those dark lines is due to
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a specific chemical element.
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Each element has its own series of lines
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that are specific to it.
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(narrator) Each chemical element absorbs light
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at specific frequencies,
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removing a strip from the spectrum.