WEBVTT

00:00:04.634 --> 00:00:10.567
[dramatic percussion music]

00:00:18.667 --> 00:00:20.167
- HEY, THERE.

00:00:20.167 --> 00:00:21.601
WELCOME TO "NASA LAUNCHPAD."

00:00:21.601 --> 00:00:23.267
I'M YOUR HOST, AMBER WHALEN.

00:00:23.267 --> 00:00:25.767
TODAY WE'RE GOING TO BE
TAKING A LOOK AT OUR MOON.

00:00:25.767 --> 00:00:28.467
YEAH, I KNOW.
WE'VE ALL SEEN IT BEFORE.

00:00:28.467 --> 00:00:29.968
BUT IF IT WEREN'T FOR THE MOON,

00:00:29.968 --> 00:00:32.167
THERE'S A PRETTY GOOD CHANCE
THAT NONE OF US WOULD BE HERE.

00:00:32.167 --> 00:00:33.467
WHY'S THAT?

00:00:33.467 --> 00:00:36.133
WELL, IN SHORT, THE MOON
HAS STABILIZING EFFECTS

00:00:36.133 --> 00:00:38.000
ON THE EARTH'S AXIS OF ROTATION,

00:00:38.000 --> 00:00:40.033
ALLOWING
FOR MORE STABLE CLIMATES.

00:00:40.033 --> 00:00:42.200
FOR INSTANCE,
SEASONS COME AND GO SLOWLY

00:00:42.200 --> 00:00:43.400
THROUGHOUT THE YEAR.

00:00:43.400 --> 00:00:45.000
IF IT WEREN'T
FOR THIS STABILITY,

00:00:45.000 --> 00:00:47.701
COMPLEX ORGANISMS
WOULD NEVER HAVE COME TO BE.

00:00:47.701 --> 00:00:50.968
SO THAT BEING SAID, WE CAN ALL
SPARE A LITTLE TIME

00:00:50.968 --> 00:00:52.801
TO LEARN A THING OR TWO
ABOUT OUR MOON.

00:00:52.801 --> 00:00:54.267
IT'S THE LEAST WE CAN DO.

00:00:54.267 --> 00:00:55.968
"APOGEE" AND "PERIGEE":

00:00:55.968 --> 00:00:57.100
MEAN ANYTHING TO YOU?

00:00:57.100 --> 00:00:59.767
YEAH, ME EITHER,
UNTIL RECENTLY, THAT IS.

00:00:59.767 --> 00:01:02.100
THE TWO WORDS
ARE ASTRONOMICAL TERMS.

00:01:02.100 --> 00:01:05.400
"APOGEE" MEANS "FAR AWAY,"
AND "PERIGEE" MEANS "NEARBY."

00:01:05.400 --> 00:01:08.234
SO HOW CAN THE MOON
BE FAR AWAY AT TIMES

00:01:08.234 --> 00:01:09.868
YET NEARBY AT OTHERS?

00:01:09.868 --> 00:01:13.100
TURNS OUT IT HAS TO DO WITH
THE MOON'S ORBIT AROUND EARTH.

00:01:13.100 --> 00:01:14.734
INSTEAD OF IN A PERFECT CIRCLE,

00:01:14.734 --> 00:01:16.334
THE MOON TRAVELS
AROUND THE EARTH

00:01:16.334 --> 00:01:18.300
IN AN ELLIPTICAL ORBIT.

00:01:18.300 --> 00:01:20.334
AT ONE EXTREME OF THE ELLIPSE,
THE APOGEE,

00:01:20.334 --> 00:01:21.968
THE MOON IS FURTHEST
FROM THE EARTH.

00:01:21.968 --> 00:01:24.434
BUT AT THE OTHER EXTREME,
THE PERIGEE,

00:01:24.434 --> 00:01:27.734
IT'S A TEENSY BIT CLOSER,
ABOUT 50,000 KILOMETERS CLOSER.

00:01:27.734 --> 00:01:30.601
OKAY, SO WE KNOW THAT
WHEN THERE'S A PERIGEE MOON,

00:01:30.601 --> 00:01:32.501
IT'S DEFINITELY CLOSER TO EARTH.

00:01:32.501 --> 00:01:34.834
BUT DOES IT MAKE A DIFFERENCE?
YOU BET.

00:01:34.834 --> 00:01:37.534
BUT YOU PROBABLY WON'T BE ABLE
TO MEASURE THIS ONE ON YOUR OWN,

00:01:37.534 --> 00:01:39.167
SO YOU'RE JUST GONNA
HAVE TO TRUST ME.

00:01:39.167 --> 00:01:41.767
OR YOU CAN TAKE A LOOK AT THIS.

00:01:41.767 --> 00:01:43.434
HERE ARE TWO PICTURES
OF OUR MOON

00:01:43.434 --> 00:01:49.334
TAKEN IN GREECE AT TWO DIFFERENT
TIMES IN THE YEAR.

00:01:49.334 --> 00:01:52.033
SIDE BY SIDE, YOU CAN SEE
THE DIFFERENCE IN SIZE.

00:01:52.033 --> 00:01:54.534
SO WE KNOW THAT THE APOGEE
AND PERIGEE CYCLE

00:01:54.534 --> 00:01:55.934
IS NOT OUT OF THE ORDINARY.

00:01:55.934 --> 00:01:57.901
BUT COULD IT AFFECT
YOUR LIFE HERE ON EARTH?

00:01:57.901 --> 00:01:59.367
ACTUALLY, IT COULD.

00:01:59.367 --> 00:02:01.033
HERE'S DR. STEN ODENWALD,

00:02:01.033 --> 00:02:03.701
NASA ASTRONOMER AT NASA GODDARD
SPACE FLIGHT CENTER,

00:02:03.701 --> 00:02:04.834
TO EXPLAIN.

00:02:04.834 --> 00:02:07.033
- IT TURNS OUT
THAT THE PERIGEE MOON,

00:02:07.033 --> 00:02:10.934
WHEN THAT HAPPENS AT THE TIME
OF THE SPRING HIGH TIDE,

00:02:10.934 --> 00:02:14.901
PRODUCES A MUCH HIGHER
THAN NORMAL HIGH TIDE.

00:02:14.901 --> 00:02:16.868
AND IF YOU'RE LIVING
IN COASTAL AREAS,

00:02:16.868 --> 00:02:18.901
ROUGHLY EVERY 1 1/2 YEARS,

00:02:18.901 --> 00:02:21.667
YOU HAVE TO WORRY
ABOUT THE HIGH, HIGH TIDES.

00:02:21.667 --> 00:02:24.167
EVERYBODY'S WORRIED
ABOUT SEA LEVEL RISE.

00:02:24.167 --> 00:02:26.067
THIS IS JUST ANOTHER EFFECT
ON TOP OF THAT

00:02:26.067 --> 00:02:28.200
THAT CAN ADD
TO COASTAL FLOODING.

00:02:28.200 --> 00:02:30.200
- AND WHY DOES NASA CARE
ABOUT THE MOON?

00:02:30.200 --> 00:02:31.934
WELL, THERE ARE A LOT
OF REASONS,

00:02:31.934 --> 00:02:34.133
SO I'LL LET DR. ODENWALD
TAKE IT AWAY.

00:02:34.133 --> 00:02:35.834
- NASA IS INTERESTED
IN THE MOON

00:02:35.834 --> 00:02:39.400
BECAUSE IT'S OUR NEAREST
CELESTIAL BODY.

00:02:39.400 --> 00:02:42.367
AND IT'S ONE THAT WE HAVE
ACTUALLY VISITED

00:02:42.367 --> 00:02:44.701
WITH THE APOLLO PROGRAM.

00:02:44.701 --> 00:02:47.367
TODAY WE'RE INTERESTED
IN GOING BACK TO THE MOON

00:02:47.367 --> 00:02:49.801
BECAUSE WE REALIZE THAT IT'S,
QUITE LITERALLY,

00:02:49.801 --> 00:02:52.834
GOING TO BE OUR STEPPING-STONE
TO TRAVELING TO MARS

00:02:52.834 --> 00:02:55.133
AND TO THE DISTANT PLANETS
AND BEYOND.

00:02:55.133 --> 00:02:57.834
SO WE STILL NEED TO DO
A LOT OF HOMEWORK

00:02:57.834 --> 00:02:59.767
FOR HOW TO NOT ONLY
GET TO THE MOON,

00:02:59.767 --> 00:03:01.934
WHICH WE KNOW HOW TO DO,

00:03:01.934 --> 00:03:03.133
BUT ONCE WE GET THERE,

00:03:03.133 --> 00:03:04.467
WE HAVE TO LEARN
HOW TO STAY THERE

00:03:04.467 --> 00:03:06.400
FOR AN APPRECIABLE AMOUNT
OF TIME,

00:03:06.400 --> 00:03:08.334
NOT JUST A COUPLE OF HOUR VISIT

00:03:08.334 --> 00:03:11.267
BUT LITERALLY STAY THERE
FOR MONTHS AND MONTHS AT A TIME.

00:03:11.267 --> 00:03:13.701
SO THAT'S REALLY
THE BIG CHALLENGE.

00:03:13.701 --> 00:03:16.300
- OKAY, SO WHILE WE'RE
ON THE SUBJECT OF OUR MOON,

00:03:16.300 --> 00:03:19.000
HAVE ANY OF YOU EVER NOTICED
THAT EVERY ONCE IN A WHILE,

00:03:19.000 --> 00:03:21.334
THE MOON LOOKS TWO,
MAYBE THREE TIMES LARGER

00:03:21.334 --> 00:03:22.534
THAN IT NORMALLY DOES?

00:03:22.534 --> 00:03:24.334
WELL, I HAVE.

00:03:24.334 --> 00:03:25.901
NOW, MY FIRST NOTION
WAS THAT THE MOON

00:03:25.901 --> 00:03:28.100
WAS HURTLING TOWARDS THE EARTH
AT TOP SPEED.

00:03:28.100 --> 00:03:30.334
BUT AS TIME PASSED
AND THE MOON ROSE IN THE SKY,

00:03:30.334 --> 00:03:33.267
I NOTICED THAT IT ACTUALLY
APPEARED TO BE GETTING SMALLER.

00:03:33.267 --> 00:03:36.000
SO MY SECOND NOTION
WAS TO GOOGLE IT.

00:03:36.000 --> 00:03:38.300
TURNS OUT IT'S ALL AN ILLUSION.

00:03:38.300 --> 00:03:41.734
SCIENTISTS HAVE NAMED THIS
LUNAR DECEPTION "MOON ILLUSION."

00:03:41.734 --> 00:03:44.734
USUALLY, IF THE MOON APPEARS
TO BE LARGER THAN NORMAL,

00:03:44.734 --> 00:03:46.601
IT WILL BE CLOSER TO THE HORIZON

00:03:46.601 --> 00:03:48.334
AS OPPOSED TO HIGHER
IN THE NIGHT SKY.

00:03:48.334 --> 00:03:49.801
AND TO BE HONEST,

00:03:49.801 --> 00:03:52.167
SCIENTISTS DON'T KNOW FOR SURE
WHY THE MOON DOES THIS.

00:03:52.167 --> 00:03:53.667
THERE ARE THEORIES, THOUGH,

00:03:53.667 --> 00:03:55.234
DOZENS OF THEM, IN FACT.

00:03:55.234 --> 00:03:56.567
IN ONE SINGLE BOOK,

00:03:56.567 --> 00:03:59.734
THE EDITOR PUT TOGETHER
24 OF HIS FAVORITE THEORIES.

00:03:59.734 --> 00:04:02.200
ONE OF THE MOST POPULAR
IS BASED ON AN ILLUSION

00:04:02.200 --> 00:04:04.033
THAT ALL OF YOU
ARE PROBABLY FAMILIAR WITH,

00:04:04.033 --> 00:04:05.601
THE PONZO ILLUSION.

00:04:05.601 --> 00:04:07.033
WHEN YOU LOOK AT THIS PICTURE,

00:04:07.033 --> 00:04:08.868
IT APPEARS THAT THE YELLOW LINE
AT THE TOP

00:04:08.868 --> 00:04:11.133
IS LARGER THAN THE YELLOW LINE
AT THE BOTTOM.

00:04:11.133 --> 00:04:13.133
TURNS OUT THEY'RE THE SAME SIZE.

00:04:13.133 --> 00:04:14.934
THE REASON:
THE HIGHER YELLOW LINE

00:04:14.934 --> 00:04:16.501
APPEARS LONGER
BECAUSE IT SPANS

00:04:16.501 --> 00:04:18.868
A GREATER APPARENT DISTANCE
BETWEEN THE RAILS.

00:04:18.868 --> 00:04:20.133
THIS TRICKERY OF THE EYE

00:04:20.133 --> 00:04:22.033
IS THOUGHT BY SOME
TO BE WHAT THE MOON DOES.

00:04:22.033 --> 00:04:23.901
BUT INSTEAD OF CONVERGING LINES,

00:04:23.901 --> 00:04:26.667
IT'S THE TREES AND BUILDINGS
THAT WE SEE IN OUR FOREGROUND

00:04:26.667 --> 00:04:28.167
THAT TRICKS US
INTO THINKING THE MOON

00:04:28.167 --> 00:04:29.968
IS ACTUALLY BIGGER THAN IT IS.

00:04:29.968 --> 00:04:32.067
AGAIN, THIS IS JUST ONE THEORY.

00:04:32.067 --> 00:04:34.701
TURNS OUT WHEN PILOTS
ARE FLYING AT HIGH ALTITUDES,

00:04:34.701 --> 00:04:36.334
THEY SEE THE MOON ILLUSION TOO.

00:04:36.334 --> 00:04:37.701
ONLY DIFFERENCE:

00:04:37.701 --> 00:04:39.701
THEY DON'T HAVE TREES
AND BUILDINGS IN THEIR VIEW.

00:04:39.701 --> 00:04:41.033
WHATEVER THE REASON IS,

00:04:41.033 --> 00:04:42.868
YOU CAN REST ASSURED
THAT THE MOON

00:04:42.868 --> 00:04:44.734
WILL NOT COLLIDE WITH EARTH.

00:04:44.734 --> 00:04:46.334
AND YOU CAN ACTUALLY PROVE
TO YOURSELF

00:04:46.334 --> 00:04:47.667
THAT THE MOON IS THE SAME SIZE

00:04:47.667 --> 00:04:49.200
NO MATTER WHERE IT IS
IN THE SKY.

00:04:49.200 --> 00:04:51.534
JUST HOLD A SMALL OBJECT,
SAY, A DIME,

00:04:51.534 --> 00:04:54.033
AT ARM'S LENGTH,
ABOUT 60 CENTIMETERS AWAY,

00:04:54.033 --> 00:04:55.267
WITH ONE EYE CLOSED.

00:04:55.267 --> 00:04:58.400
POSITION IT NEXT
TO THE SEEMINGLY LARGE MOON.

00:04:58.400 --> 00:05:00.200
WHEN THE MOON IS HIGHER
IN THE SKY,

00:05:00.200 --> 00:05:02.000
HOLD THAT SAME OBJECT
NEAR THE MOON,

00:05:02.000 --> 00:05:04.200
AND YOU CAN SEE THAT THERE IS
NO CHANGE IN SIZE.

00:05:04.200 --> 00:05:05.734
THIS IS JUST A LITTLE TRICK

00:05:05.734 --> 00:05:07.968
USING SOMETHING CALLED
ANGULAR SIZE,

00:05:07.968 --> 00:05:10.968
THE SAME TECHNIQUE SCIENTISTS
AND MATHEMATICIANS USE

00:05:10.968 --> 00:05:12.501
TO MEASURE THINGS INDIRECTLY

00:05:12.501 --> 00:05:14.901
BECAUSE THEY ARE TOO FAR AWAY
TO ACTUALLY MEASURE.

00:05:14.901 --> 00:05:16.667
FOR THE BEST AND BIGGEST VIEW
OF OUR MOON,

00:05:16.667 --> 00:05:18.267
FIND OUT WHEN THE NEXT
PERIGEE MOON IS

00:05:18.267 --> 00:05:20.667
AND TAKE A GANDER AT IT
WHEN IT'S CLOSER TO THE HORIZON.

00:05:20.667 --> 00:05:22.033
THAT WAY, THE MOON ILLUSION

00:05:22.033 --> 00:05:24.033
WILL MAKE THE PERIGEE MOON
APPEAR EVEN BIGGER.

00:05:24.033 --> 00:05:26.033
THANKS FOR TUNING IN
TO "NASA LAUNCHPAD."

00:05:26.033 --> 00:05:27.200
WE'LL CATCH YOU NEXT TIME.