WEBVTT

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[dramatic percussion music]

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- HEY, WELCOME
TO "NASA LAUNCHPAD."

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I'M YOUR HOST,
AUDREY STAPLES.

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ECLIPSES.

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YEAH, I KNOW WE'RE ALWAYS
TALKING ABOUT NASA E-CLIPS

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HERE ON "LAUNCHPAD,"

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BUT THOSE ARE THE SHORT
VIDEO CLIPS YOU'RE WATCHING.

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AND, NO, WE'RE NOT TALKING ABOUT
THE BOOK IN THAT VAMPIRE SERIES.

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COME ON, FOCUS HERE.

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WE'RE TALKING ABOUT ONE
OF THE MOST SPECTACULAR

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NATURAL PHENOMENA
YOU CAN WITNESS HERE ON EARTH

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OR ANYWHERE ELSE
IN THE SOLAR SYSTEM,

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FOR THAT MATTER.

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WHEN A SOLAR ECLIPSE OCCURS,

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LIGHT FROM THE SUN
IS BLOCKED.

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ACTUALLY, THAT DOES SOUND LIKE
A GOOD PREMISE

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FOR A VAMPIRE STORY.

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LET ME GO WRITE THAT DOWN.

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IN THE MEANTIME,
HERE'S AN EXPERT ON ECLIPSES,

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FRED ESPENAK,
ALSO KNOWN AS MR. ECLIPSE,

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FROM NASA GODDARD
SPACE FLIGHT CENTER,

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TO REALLY HELP US UNDERSTAND

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THESE INCREDIBLE
ASTRONOMICAL EVENTS.

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AND JUST KEEP IN MIND,

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THESE ANIMATIONS
YOU'RE ABOUT TO SEE

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ARE NOT TO SCALE.

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- A TOTAL ECLIPSE OF THE SUN

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IS ONE OF THE MOST
AWE-INSPIRING SIGHTS

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IN ALL OF NATURE,

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AND IT'S ALL MADE POSSIBLE
DUE TO THE UNIQUE GEOMETRY

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IN THE DISTANCES AND SIZES
OF THE SUN AND MOON

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AS SEEN FROM THE EARTH.

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AS WE ALL KNOW,
THE MOON ORBITS THE EARTH,

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AND THE EARTH ORBITS THE SUN.

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AND CELESTIAL MECHANICS
ALLOWS US

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TO CALCULATE THESE ORBITS
WITH GREAT PRECISION.

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WHEN THE MOON PASSES
BETWEEN THE EARTH AND THE SUN,

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WE SAY THAT THE MOON
IS IN THE NEW PHASE.

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AN ECLIPSE OF THE SUN CAN ONLY
OCCUR WHEN THE MOON IS NEW.

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HOWEVER, NOT ALL NEW MOONS
PRODUCE A SOLAR ECLIPSE.

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THE MOON'S ORBIT
AROUND THE EARTH

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IS TILTED ABOUT FIVE DEGREES
TO THE PLANE

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OF THE EARTH'S ORBIT
AROUND THE SUN.

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AS A RESULT,
THE MOON SPENDS MOST OF ITS TIME

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EITHER ABOVE OR BELOW
THE EARTH'S ORBITAL PLANE.

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THE MOON PASSES
THROUGH THE PLANE ONLY TWICE

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DURING EACH OF ITS ORBITS.

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IF THE MOON ALSO HAPPENS TO BE
IN A NEW MOON PHASE

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WHEN IT CROSSES
EARTH'S ORBITAL PLANE,

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THEN A SOLAR ECLIPSE WILL OCCUR.

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MOST ECLIPSES ARE PARTIAL,
BECAUSE NEW MOON TAKES PLACE

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JUST BEFORE OR AFTER THE MOON
CROSSES THE ORBITAL PLANE.

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BUT IF THE TIMING IS RIGHT,
A TOTAL ECLIPSE OF THE SUN

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OCCURS JUST AS THE CENTER
OF THE MOON

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PASSES DIRECTLY IN FRONT
OF THE CENTER OF THE SUN.

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THE PATH THAT THE MOON'S SHADOW
MAKES OVER THE EARTH

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DURING A TOTAL ECLIPSE
IS CALLED THE PATH OF TOTALITY.

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TO SEE A TOTAL ECLIPSE,

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YOU MUST BE
IN THE PATH OF TOTALITY.

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AS A TOTAL SOLAR ECLIPSE BEGINS,

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A GHOSTLY SILHOUETTE
LOOMS INTO VIEW,

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FRAMED BY A WHITE GLOW

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THAT CREATES A HALO
AROUND THE DARKENED SUN.

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IN THE FINAL SECONDS,
THE SUN'S REMAINING RAYS

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SHINE THROUGH DEEP VALLEYS
ALONG THE EDGE OF THE MOON.

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AT THE SAME TIME,
THE SUN'S CORONA APPEARS,

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SURROUNDED
BY THE MOON'S BLACK DISK.

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BEFORE THE LAST BEAD
OF SUNLIGHT VANISHES,

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THE EFFECT RESEMBLES
A COSMIC DIAMOND RING.

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SUDDENLY, TOTALITY.

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THE BRIGHT SUN IS GONE.

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A BLACK DISK
SURROUNDED BY A PALE HALO

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NOW STANDS IN ITS PLACE.

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THE SUN'S CORONA
IS THE MOST STUNNING,

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MOST BEAUTIFUL,
AND MOST UNEXPECTED FEATURE

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OF A TOTAL ECLIPSE.

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AS THE OUTERMOST LAYER
OF THE SUN'S ATMOSPHERE,

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THE CORONA IS EXTREMELY HOT,

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WITH A TEMPERATURE
OF 2 MILLION DEGREES CELSIUS.

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THE MOONS OF OTHER PLANETS
IN OUR SOLAR SYSTEM

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PRODUCE ECLIPSES,

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BUT NONE OF THEM
HAVE THE PERFECT SIZE FIT

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THAT TOTAL ECLIPSES HAVE
FROM EARTH.

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IN SOME CASES,
THE MOONS HAVE ANGULAR SIZES

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THAT ARE MUCH LARGER
THAN THE SUN.

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IN OTHER CASES,
THE MOONS ARE MUCH TOO SMALL

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AND TOO FAR AWAY
TO COVER THE SUN.

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WE CALL THIS KIND OF AN EVENT
A TRANSIT.

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OUR NASA MARS ROVERS
HAVE BOTH PHOTOGRAPHED

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MARTIAN MOONS PHOBOS AND DEIMOS
AS THEY TRANSITED THE SUN.

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PRETTY COOL.

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- ALL RIGHT,
I'VE GOT TO BE HONEST.

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I DON'T GET IT.

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HOW CAN THE MOON, WHICH IS ABOUT
1/6 THE SIZE OF EARTH,

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COVER UP THE SUN,

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WHICH IS 400 TIMES LARGER
IN DIAMETER THAN THE MOON?

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- TO COMPARE THE RELATIVE SIZES
OF THE EARTH, MOON, AND SUN,

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WE'LL USE THIS BASKETBALL
AND THIS TENNIS BALL.

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LET'S CALL
THIS BASKETBALL EARTH

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AND THIS TENNIS BALL
THE MOON.

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THESE ARE THE RELATIVE SIZES

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OF THE EARTH AND MOON
TO EACH OTHER.

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SO WHAT DO YOU THINK
WE COULD USE

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TO REPRESENT THE SIZE
OF THE SUN?

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A SMALL CAR?

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THINK BIGGER.

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THE SUN WOULD BE 90 FEET
IN DIAMETER,

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ABOUT THE SIZE
OF THIS OFFICE BUILDING.

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SO HOW IS IT THAT
THIS TENNIS BALL-SIZED MOON

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CAN BLOCK
THIS BUILDING-SIZED SUN?

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THE ANSWER IS ANGULAR SIZE.

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ANGULAR SIZE
IS THE MEASURE OF AN ANGLE

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FORMED BY EXTENDING
IMAGINARY LINES OUTWARD

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FROM A SPECIFIC POINT
TO SPAN THE WIDTH OF AN OBJECT.

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THE IMAGINARY LINES
FORM A TRIANGLE.

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ANGLES ARE MEASURED IN DEGREES.

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TWO OBJECTS IN SPACE
MAY APPEAR TO BE THE SAME SIZE

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IF THEIR DISTANCES AND DIAMETERS
ARE PROPORTIONAL

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AND IF THEY ARE VIEWED
FROM THE SAME POSITION ON EARTH.

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THE DIAMETER OF THE SUN
IS 400 TIMES LARGER

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THAN THE DIAMETER OF THE MOON,

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BUT THE SUN IS ALSO 400 TIMES
FURTHER AWAY FROM THE EARTH

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THAN THE MOON IS
FROM OUR PLANET.

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IF YOU EXTEND IMAGINARY LINES
THAT SPAN THESE TWO OBJECTS

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TO OUR VIEWPOINT ON EARTH,
YOU CAN SEE

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THAT TWO SIMILAR TRIANGLES
ARE FORMED.

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THE ANGLES FORMED
AT THE VIEWPOINT

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ARE THE SAME FOR BOTH OBJECTS,

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MAKING THE ANGULAR SIZE
OF THESE OBJECTS EQUAL.

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WHEN THESE BODIES
LINE UP EXACTLY,

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THE MOON APPEARS TO BE
THE SAME SIZE AS THE SUN,

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CREATING A TOTAL SOLAR ECLIPSE.

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THIS FORTUNATE COINCIDENCE
IS RESPONSIBLE

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FOR THE PERFECT FIT
OF THE TOTAL SOLAR ECLIPSE,

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ONE OF THE MOST
SPECTACULAR EVENTS

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YOU CAN POSSIBLY WITNESS
IN OUR SOLAR SYSTEM.

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- UNLIKE, SAY,
THE VENUS TRANSIT,

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SOLAR ECLIPSES CAN HAPPEN
SEVERAL TIMES A YEAR.

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IN FACT,
IN THE 21ST CENTURY ALONE,

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THERE WILL BE 224
SOLAR ECLIPSES.

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OF THESE,
68 WILL BE TOTAL ECLIPSES.

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OF COURSE, JUST BECAUSE
AN ECLIPSE WILL HAPPEN

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DOESN'T NECESSARILY MEAN
THAT YOU'LL BE ABLE TO SEE IT.

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DUE TO THE POSITION OF THE EARTH
IN ITS ORBIT AROUND THE SUN,

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ONLY CERTAIN AREAS
ARE ABLE TO SEE EACH ECLIPSE.

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BUT DON'T WORRY,
WITH A LITTLE RESEARCH,

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YOU CAN FIND OUT EXACTLY
WHEN THE NEXT SOLAR ECLIPSE

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WILL BE BLOTTING OUT THE SUN
IN A TOWN NEAR YOU.

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CHECK OUT NASA'S WEBSITE
ON ECLIPSES AT:

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BUT REMEMBER,
EVEN IF THERE'S AN ECLIPSE,

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YOU SHOULDN'T LOOK DIRECTLY
AT THE SUN,

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BECAUSE IT CAN SERIOUSLY DAMAGE
YOUR EYES.

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THAT'S IT FOR NOW.

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UNTIL NEXT TIME,
I'M AUDREY STAPLES.

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FOR "NASA LAUNCHPAD,"
THANKS FOR WATCHING.