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, SCOTT BEDNAR.

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WE'VE TALKED ABOUT
SOME AWESOME NASA RESEARCH

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USING TRANSIT METHODS
TO STUDY EXOPLANETS,

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YOU KNOW, EXOPLANETS,

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THE PLANETS THAT ARE OUTSIDE
OUR SOLAR SYSTEM.

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NASA'S KEPLER MISSION
AND THE OBSERVATIONS DONE

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BY DR. DEMING AT KITT PEAK
NATIONAL OBSERVATORY

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ARE BOTH LOOKING
AT REALLY FARAWAY WORLDS

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TO SEE JUST WHAT THEY CAN LEARN
ABOUT THESE PLACES.

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BUT THE USE
OF THE TRANSIT METHOD

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DOESN'T JUST SERVE SCIENTISTS
LOOKING SO FAR AWAY FROM HOME.

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IN FACT, OUR CLOSEST
PLANETARY NEIGHBOR, VENUS,

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COMPLETES TRANSITS
ACROSS OUR SUN.

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FOR MORE INFORMATION
ON THESE VENUS TRANSITS,

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LET'S CHECK IN
WITH DR. JANET LUHMANN,

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A SCIENTIST AT THE UNIVERSITY
OF CALIFORNIA

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SPACE SCIENCES LAB.

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- A VENUS TRANSIT OCCURS

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WHEN VENUS CROSSES
THE DISK OF THE SUN

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AS SEEN BY AN OBSERVER.

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IT'S LIKE A SOLAR ECLIPSE

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IN THAT VENUS IS LOCATED
ON THE LINE

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BETWEEN THE SUN AND THE EARTH

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AND THEREFORE BLOCKS
SOME OF THE SUN'S LIGHT.

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HOWEVER, IN A VENUS TRANSIT,

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THE AMOUNT OF SUNLIGHT BLOCKED
IS VERY SMALL

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COMPARED TO A SOLAR ECLIPSE,

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AND SO THE OBSERVER WHO IS
UNAWARE WILL NEVER NOTICE IT.

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VENUS' CIRCULAR SHADOW
IS MUCH, MUCH SMALLER

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THAN OUR MOON'S SHADOW.

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EVEN THOUGH VENUS IS NEARLY
THE SIZE OF THE EARTH,

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IT IS MUCH FARTHER AWAY
THAN THE MOON.

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IN CLEAR WEATHER, VENUS TRANSITS
ARE VISIBLE WITH THE NAKED EYE

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OR WITH A SMALL TELESCOPE,

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WHICH IS WHY THEY BECAME POPULAR
IN THE 1600s.

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- SO UNLIKE THE TRANSITS
OBSERVED BY THE KEPLER MISSION

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OR BY OBSERVERS USING
HUGE ASTRONOMICAL TELESCOPES,

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THE VENUS TRANSIT IS ONE

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THAT YOU CAN ACTUALLY SEE
FOR YOURSELF.

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NOW, REMEMBER, YOU SHOULD NEVER
LOOK AT THE SUN DIRECTLY.

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SO IN ORDER TO OBSERVE
THE VENUS TRANSIT,

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YOU NEED TO USE
A SAFE VIEWING TECHNIQUE

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EITHER WITH PROTECTION,
SOLAR FILTERS, OR PROJECTORS.

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FOR MORE INFORMATION ON THESE
SAFE VIEWING TECHNIQUES,

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GO TO NASA'S SUN-EARTH DAY
WEBSITE AT SUNEARTHDAY.NASA.GOV.

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THE MOST RECENT VENUS TRANSIT

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ACTUALLY TOOK PLACE
ON JUNE 8, 2004.

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AND AT THAT TIME,

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RESEARCHERS WERE ABLE
TO GATHER A LOT OF INFORMATION.

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FOR STARTERS, THEY WERE ABLE
TO VERIFY THE DISTANCE IN AU,

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OR ASTRONOMICAL UNITS,

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WITH GLOBALLY ORGANIZED EFFORTS

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AND 21ST-CENTURY TECHNOLOGY
LOOKING AT PARALLAX.

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WHAT'S PARALLAX?

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WELL, LET'S HEAR
FROM DR. STEN ODENWALD,

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NASA ASTRONOMER AT NASA
GODDARD SPACE FLIGHT CENTER.

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- THE ANSWER IS THAT ASTRONOMERS

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USED A GEOMETRIC TECHNIQUE
CALLED PARALLAX

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TO DETERMINE THE DISTANCE
BETWEEN THE EARTH AND THE SUN.

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PARALLAX IS THE APPARENT
CHANGE IN POSITION OF AN OBJECT

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WHEN YOU LOOK AT IT
FROM TWO DIFFERENT STATIONS

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OR POINTS OF VIEW.

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IT SOUNDS MYSTERIOUS,

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BUT YOU USE THIS TECHNIQUE
ALL THE TIME.

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FOR EXAMPLE,

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LET ME SHOW YOU HOW PARALLAX
WORKS BY USING MY THUMB

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AND THAT ROCKET
IN THE BACKGROUND.

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FIRST, HOLD YOUR THUMB OUT
AT ARM'S LENGTH.

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NOW LOOK AT YOUR THUMB
WITH YOUR LEFT EYE OPEN

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AND YOUR RIGHT EYE CLOSED.

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WHAT DO YOU NOTICE ABOUT
THE POSITION OF YOUR THUMB?

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THERE SEEMS TO BE AN APPARENT
CHANGE IN POSITION OF YOUR THUMB

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FROM TWO POINTS OF VIEW,

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YOUR LEFT EYE
AND YOUR RIGHT EYE.

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YOUR BRAIN USES THIS INFORMATION

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TO FIGURE OUT HOW FAR AWAY
THINGS ARE FROM YOU.

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BY OBSERVING THE APPARENT
SHIFTING POSITION OF VENUS

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AGAINST THE BACKGROUND
OF THE SOLAR DISK

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AS SEEN FROM TWO DIFFERENT
PLACES ON EARTH,

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ASTRONOMERS WERE ABLE TO USE
THIS PARALLAX SHIFT

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TO DETERMINE THE DISTANCE
FROM THE EARTH TO THE SUN.

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- BUT THAT'S NOT ALL.

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ASIDE FROM EARTH-BASED
OBSERVATIONS,

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THE TRACE SATELLITE WAS ABLE
TO OBSERVE THE VENUS TRANSIT,

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AND IT CAPTURED AMAZING IMAGES
AND VIDEOS

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OF THAT JUNE 2004 TRANSIT.

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TAKE A LOOK AT A FEW OF THESE.

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WAIT A MINUTE.
THAT LAST ONE'S NOT VENUS.

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IT'S ACTUALLY
THE TRANSIT OF MERCURY

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ACROSS THE SUN IN 2003.

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THAT'S RIGHT.

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MERCURY TRANSITS ACROSS THE SUN
JUST LIKE VENUS.

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BUT MERCURY TRANSITS
MUCH MORE OFTEN,

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IN PART BECAUSE MERCURY
IS CLOSER TO THE SUN

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AND IT ORBITS IT MORE RAPIDLY.

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WHILE TRANSITS OF MERCURY HAPPEN
ABOUT 13 OR 14 TIMES A CENTURY,

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A TRANSIT OF VENUS ONLY HAPPENS
FOUR TIMES EVERY 243 YEARS.

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AND RESEARCHERS CAN PREDICT
ALL OF THESE EVENTS

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BECAUSE PLANETS MOVE
IN VIRTUALLY FIXED ORBITS,

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SO THE PATTERNS OF THE ORBITS
CAN BE MAPPED.

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IT'S SORT OF LIKE WATCHING
THE TURN SIGNALS ON TWO CARS

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SITTING AT A STOPLIGHT.

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THE BLINK TIMING
FOR EACH VEHICLE IS DIFFERENT,

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AND THEY PROBABLY STARTED
AT DIFFERENT TIMES.

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BUT USUALLY, THE PATTERN WILL
LINE UP FOR ONE PERFECT BLINK

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AND THEN OFF AGAIN.

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SIMILAR IDEA.

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AND IN FACT, THE TRANSITS
OF MERCURY AND VENUS

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DO LINE UP SO THEY TAKE PLACE
AT THE SAME TIME.

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THE NEXT TIME THAT WILL HAPPEN?

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TRY JULY 26TH
OF THE YEAR 69,163.

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SO I THINK YOU'RE KIND OF
OUT OF LUCK FOR SEEING THAT ONE.

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BUT YOU DON'T HAVE
TO WAIT THAT LONG

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TO CATCH A SINGLE TRANSIT.

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THE NEXT VENUS TRANSIT

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WILL TAKE PLACE
ON JUNE 5TH AND 6TH OF 2012,

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SO YOU SHOULD BE ABLE
TO CATCH A GLIMPSE FOR YOURSELF.

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MAKE SURE YOU DON'T
MISS IT, THOUGH,

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BECAUSE THE NEXT ONE
WON'T BE AROUND

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TILL DECEMBER OF 2117.

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I GUESS WE'LL HAVE TO LEAVE
THAT ONE

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FOR THE NEXT GENERATION OR TWO
OF NASA SCIENTISTS.

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AND MARK YOUR CALENDARS NOW.

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THE NEXT TRANSIT OF MERCURY
WILL TAKE PLACE MAY 8, 2016.

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WELL, THAT'S IT FOR NOW.

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UNTIL NEXT TIME,
I AM SCOTT BEDNAR,

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AND THANK YOU FOR WATCHING
"NASA LAUNCHPAD."

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TAKE IT EASY.