[dramatic percussion music]
- HEY, THERE.
WELCOME TO "NASA LAUNCHPAD."
I'M YOUR HOST, AMBER WHALEN.
TODAY WE'RE GOING TO BE TAKING A LOOK AT OUR MOON.
YEAH, I KNOW. WE'VE ALL SEEN IT BEFORE.
BUT IF IT WEREN'T FOR THE MOON,
THERE'S A PRETTY GOOD CHANCE THAT NONE OF US WOULD BE HERE.
WHY'S THAT?
WELL, IN SHORT, THE MOON HAS STABILIZING EFFECTS
ON THE EARTH'S AXIS OF ROTATION,
ALLOWING FOR MORE STABLE CLIMATES.
FOR INSTANCE, SEASONS COME AND GO SLOWLY
THROUGHOUT THE YEAR.
IF IT WEREN'T FOR THIS STABILITY,
COMPLEX ORGANISMS WOULD NEVER HAVE COME TO BE.
SO THAT BEING SAID, WE CAN ALL SPARE A LITTLE TIME
TO LEARN A THING OR TWO ABOUT OUR MOON.
IT'S THE LEAST WE CAN DO.
"APOGEE" AND "PERIGEE":
MEAN ANYTHING TO YOU?
YEAH, ME EITHER, UNTIL RECENTLY, THAT IS.
THE TWO WORDS ARE ASTRONOMICAL TERMS.
"APOGEE" MEANS "FAR AWAY," AND "PERIGEE" MEANS "NEARBY."
SO HOW CAN THE MOON BE FAR AWAY AT TIMES
YET NEARBY AT OTHERS?
TURNS OUT IT HAS TO DO WITH THE MOON'S ORBIT AROUND EARTH.
INSTEAD OF IN A PERFECT CIRCLE,
THE MOON TRAVELS AROUND THE EARTH
IN AN ELLIPTICAL ORBIT.
AT ONE EXTREME OF THE ELLIPSE, THE APOGEE,
THE MOON IS FURTHEST FROM THE EARTH.
BUT AT THE OTHER EXTREME, THE PERIGEE,
IT'S A TEENSY BIT CLOSER, ABOUT 50,000 KILOMETERS CLOSER.
OKAY, SO WE KNOW THAT WHEN THERE'S A PERIGEE MOON,
IT'S DEFINITELY CLOSER TO EARTH.
BUT DOES IT MAKE A DIFFERENCE? YOU BET.
BUT YOU PROBABLY WON'T BE ABLE TO MEASURE THIS ONE ON YOUR OWN,
SO YOU'RE JUST GONNA HAVE TO TRUST ME.
OR YOU CAN TAKE A LOOK AT THIS.
HERE ARE TWO PICTURES OF OUR MOON
TAKEN IN GREECE AT TWO DIFFERENT TIMES IN THE YEAR.
SIDE BY SIDE, YOU CAN SEE THE DIFFERENCE IN SIZE.
SO WE KNOW THAT THE APOGEE AND PERIGEE CYCLE
IS NOT OUT OF THE ORDINARY.
BUT COULD IT AFFECT YOUR LIFE HERE ON EARTH?
ACTUALLY, IT COULD.
HERE'S DR. STEN ODENWALD,
NASA ASTRONOMER AT NASA GODDARD SPACE FLIGHT CENTER,
TO EXPLAIN.
- IT TURNS OUT THAT THE PERIGEE MOON,
WHEN THAT HAPPENS AT THE TIME OF THE SPRING HIGH TIDE,
PRODUCES A MUCH HIGHER THAN NORMAL HIGH TIDE.
AND IF YOU'RE LIVING IN COASTAL AREAS,
ROUGHLY EVERY 1 1/2 YEARS,
YOU HAVE TO WORRY ABOUT THE HIGH, HIGH TIDES.
EVERYBODY'S WORRIED ABOUT SEA LEVEL RISE.
THIS IS JUST ANOTHER EFFECT ON TOP OF THAT
THAT CAN ADD TO COASTAL FLOODING.
- AND WHY DOES NASA CARE ABOUT THE MOON?
WELL, THERE ARE A LOT OF REASONS,
SO I'LL LET DR. ODENWALD TAKE IT AWAY.
- NASA IS INTERESTED IN THE MOON
BECAUSE IT'S OUR NEAREST CELESTIAL BODY.
AND IT'S ONE THAT WE HAVE ACTUALLY VISITED
WITH THE APOLLO PROGRAM.
TODAY WE'RE INTERESTED IN GOING BACK TO THE MOON
BECAUSE WE REALIZE THAT IT'S, QUITE LITERALLY,
GOING TO BE OUR STEPPING-STONE TO TRAVELING TO MARS
AND TO THE DISTANT PLANETS AND BEYOND.
SO WE STILL NEED TO DO A LOT OF HOMEWORK
FOR HOW TO NOT ONLY GET TO THE MOON,
WHICH WE KNOW HOW TO DO,
BUT ONCE WE GET THERE,
WE HAVE TO LEARN HOW TO STAY THERE
FOR AN APPRECIABLE AMOUNT OF TIME,
NOT JUST A COUPLE OF HOUR VISIT
BUT LITERALLY STAY THERE FOR MONTHS AND MONTHS AT A TIME.
SO THAT'S REALLY THE BIG CHALLENGE.
- OKAY, SO WHILE WE'RE ON THE SUBJECT OF OUR MOON,
HAVE ANY OF YOU EVER NOTICED THAT EVERY ONCE IN A WHILE,
THE MOON LOOKS TWO, MAYBE THREE TIMES LARGER
THAN IT NORMALLY DOES?
WELL, I HAVE.
NOW, MY FIRST NOTION WAS THAT THE MOON
WAS HURTLING TOWARDS THE EARTH AT TOP SPEED.
BUT AS TIME PASSED AND THE MOON ROSE IN THE SKY,
I NOTICED THAT IT ACTUALLY APPEARED TO BE GETTING SMALLER.
SO MY SECOND NOTION WAS TO GOOGLE IT.
TURNS OUT IT'S ALL AN ILLUSION.
SCIENTISTS HAVE NAMED THIS LUNAR DECEPTION "MOON ILLUSION."
USUALLY, IF THE MOON APPEARS TO BE LARGER THAN NORMAL,
IT WILL BE CLOSER TO THE HORIZON
AS OPPOSED TO HIGHER IN THE NIGHT SKY.
AND TO BE HONEST,
SCIENTISTS DON'T KNOW FOR SURE WHY THE MOON DOES THIS.
THERE ARE THEORIES, THOUGH,
DOZENS OF THEM, IN FACT.
IN ONE SINGLE BOOK,
THE EDITOR PUT TOGETHER 24 OF HIS FAVORITE THEORIES.
ONE OF THE MOST POPULAR IS BASED ON AN ILLUSION
THAT ALL OF YOU ARE PROBABLY FAMILIAR WITH,
THE PONZO ILLUSION.
WHEN YOU LOOK AT THIS PICTURE,
IT APPEARS THAT THE YELLOW LINE AT THE TOP
IS LARGER THAN THE YELLOW LINE AT THE BOTTOM.
TURNS OUT THEY'RE THE SAME SIZE.
THE REASON: THE HIGHER YELLOW LINE
APPEARS LONGER BECAUSE IT SPANS
A GREATER APPARENT DISTANCE BETWEEN THE RAILS.
THIS TRICKERY OF THE EYE
IS THOUGHT BY SOME TO BE WHAT THE MOON DOES.
BUT INSTEAD OF CONVERGING LINES,
IT'S THE TREES AND BUILDINGS THAT WE SEE IN OUR FOREGROUND
THAT TRICKS US INTO THINKING THE MOON
IS ACTUALLY BIGGER THAN IT IS.
AGAIN, THIS IS JUST ONE THEORY.
TURNS OUT WHEN PILOTS ARE FLYING AT HIGH ALTITUDES,
THEY SEE THE MOON ILLUSION TOO.
ONLY DIFFERENCE:
THEY DON'T HAVE TREES AND BUILDINGS IN THEIR VIEW.
WHATEVER THE REASON IS,
YOU CAN REST ASSURED THAT THE MOON
WILL NOT COLLIDE WITH EARTH.
AND YOU CAN ACTUALLY PROVE TO YOURSELF
THAT THE MOON IS THE SAME SIZE
NO MATTER WHERE IT IS IN THE SKY.
JUST HOLD A SMALL OBJECT, SAY, A DIME,
AT ARM'S LENGTH, ABOUT 60 CENTIMETERS AWAY,
WITH ONE EYE CLOSED.
POSITION IT NEXT TO THE SEEMINGLY LARGE MOON.
WHEN THE MOON IS HIGHER IN THE SKY,
HOLD THAT SAME OBJECT NEAR THE MOON,
AND YOU CAN SEE THAT THERE IS NO CHANGE IN SIZE.
THIS IS JUST A LITTLE TRICK
USING SOMETHING CALLED ANGULAR SIZE,
THE SAME TECHNIQUE SCIENTISTS AND MATHEMATICIANS USE
TO MEASURE THINGS INDIRECTLY
BECAUSE THEY ARE TOO FAR AWAY TO ACTUALLY MEASURE.
FOR THE BEST AND BIGGEST VIEW OF OUR MOON,
FIND OUT WHEN THE NEXT PERIGEE MOON IS
AND TAKE A GANDER AT IT WHEN IT'S CLOSER TO THE HORIZON.
THAT WAY, THE MOON ILLUSION
WILL MAKE THE PERIGEE MOON APPEAR EVEN BIGGER.
THANKS FOR TUNING IN TO "NASA LAUNCHPAD."
WE'LL CATCH YOU NEXT TIME.