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>> HELLO AND WELCOME TO A

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SPECIAL EPISODE OF NASA SCIENCE

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LIVE.

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I'M JOY.

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I'M GLAD YOU ARE JOINING US TO

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TALK ABOUT COMET NEOWISE.

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THIS THREE MILE WIDE COMET IS

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GOING THROUGH THE NIGHT SCHOOL.

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YOU CAN LOOK UP, IF YOU ARE

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LUCKY, YOU CAN SEE IT WITH THE

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NAKED I'M.

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IT WAS AT 4:00 A.M. IN THE

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CHESAPEAKE BAY IN MARYLAND.

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YOU GET A CHANCE TO SEE IT IN

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THE EVENING JUST AFTER SUNSET.

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WE HAVE RECEIVED AMAZING IMAGES.

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WE'LL FEATURE THEM THROUGHOUT

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THE SHOW.

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COMET NEOWISE WAS DISCOVER IN

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MARCH OF THIS YEAR.

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IT'S BEEN PUTTING ON A GRAND

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SHOW AT DOWN AND NOW AT DUSK.

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IT'S THE FORMATION FROM OUR

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SOLAR SYSTEM ABOUT 4 BILLION

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YEARS AGO.

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THEY HAVE GASSES AND DUST IN A

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GLOWING HEAD.

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THIS FORMS THE TAIL YOU SEE

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STRETCHING ACROSS THE SKY.

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TODAY WE HAVE TWO NASA EXPERTS

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THEY'RE ANSWER KEY QUESTIONS

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ABOUT THIS FASCINATING OBJECT.

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PLEASE SEND YOUR QUESTIONS USING

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THE #ASKNASA OR WRITE IN THE

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COMMENTS.

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LET'S GET STARTED.

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EMILY IS THE COINVESTIGATOR AND

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JAMES IS THE DEPUTY INVESTIGATOR

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FROM NASA.

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THANK YOU FOR JOINING US.

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>> THANKS FOR HAVING US.

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>> GREAT TO BE HERE.

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>> SO WE ARE ALL EXCITED ABOUT

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THE OPPORTUNITY TO SEE COMMENT

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NEOWISE IN THE SKY.

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I'M CURIOUS, WHAT IS THE

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DIFFERENCE BETWEEN A COMET AND

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AN ASTEROID?

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>> THEY ARE BOTH OBJECTS IN OUR

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SOLAR SYSTEM THAT ORBIT THROUGH

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THE DIFFERENT AREAS.

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THE ASTEROIDS ARE BETWEEN MARS

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AND JUPITER AND THE COMETS ARE

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IN A WIDER AREA.

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ASTEROIDS ARE ROCKY AND COMETS

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ARE ICY MUD BALLS, A COMBINATION

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OF WATER, ICE, CARBON DIOXIDE

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AND DUST AS WELL.

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>> HOW WAS COMET NEOWISE FIRST

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DISCOVERED?

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>> COMET NEOWISE WAS PICKED UP

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BY THE SURVEY AT THE END OF

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MARCH.

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NEOWISE STANDS FOR THIS.

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SO THIS COMMENT WAS FIRST PICKED

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UP AT THE END OF MARCH AS PART

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OF OUR AUTOMATED PROCESSING.

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IT GOES THROUGH A SYSTEM THAT

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TRIES TO IDENTIFY MOVING

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OBJECTS.

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SO AS PART OF THAT REVIEW WE

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WERE LOOKING AT, THIS LOOKS LIKE

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A COMET.

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WE CAN SEE A CLEAR, FUZZY CLOUD

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AROUND IT.

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HERE'S A NEW OBJECT, IT LOOKS TO

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BE COMETARY.

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IT WAS GOING AROUND THE SUN AND

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THERE WAS A CHANCE IT COULD

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BECOME VERY BRIGHT.

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WE WERE CROSSING OUR FINGERS AND

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WE GOT LUCKY THAT IT TURNED OUT

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TO BE A SPECTACULAR SIGHT.

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>> IT'S REALLY, REALLY STUNNING.

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SO WHY IS IT NAMED NEOWISE?

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>> SO THIS IS A TRADITION IN

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ASTRONOMY THAT GOES BACK

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CENTURIES.

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THEY ARE NAMED AFTER THEIR

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DISCOVERER OR FIRST PERSON WHO

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REPORTED IT IN THE JOURNALS OR

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LETTERS TO COLLEAGUES.

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NOW THAT MOST OF THE DISCOVERIES

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ARE DONE BY SURVEYS, THE RULES

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ARE IF IT'S FOUND BY THE SURVEY,

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IT'S NAMED AFTER THE SURVEY.

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SINCE OUR SURVEY IS NEOWISE, THE

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COMET IS NEOWISE.

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>> IS THERE ANYTHING THAT MAKES

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THIS COMMENT UNIQUE?

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>> THE FACT WE CAN SEE IT IS

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WHAT MAKES IT UNIQUE.

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IT'S QUITE RARE FOR A COMET TO

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BE BRIGHT ENOUGH THAT WE CAN SEE

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IT WITH THE NAKED EYE.

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THE LAST TIME WAS BACK IN 1995

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TO 1996.

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IT'S BEEN QUITE A WHILE.

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IT'S EXCITING TO SEE THIS NOW.

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>> WHY IS IT THAT WE CAN SEE

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COMET NEOWISE NOW?

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I UNDERSTAND IT WILL DISAPPEAR

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AT THE END OF THE MONTH.

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>> SO, WHEN IT CAME BY THE CLOSE

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PASS OF THE SUN JULY 3, THAT'S

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WHEN IT GETS THE HOTTEST.

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THE SUN BAKES OFF THESE ICES

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THAT EMILY SPOKE ABOUT AND TURNS

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THEM INTO A GAS THAT MAKES THIS

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CLOUD.

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THAT'S A COMBINATION OF MELTING

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GASSES AND DUST.

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WHETHER YOU CAN SEE A COMET OR

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NOT AND HOW BRIGHT IT APPEAR A

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FUNCTION OF GEOMETRY.

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IF ALL THE THINGS LINE UP RIGHT,

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THEN THE COMET REFLECTS ENOUGH

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OF THE SUN'S LIGHT TO SEE IT

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WITH THE NAKED EYE.

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>> WE HAVE HAD A FEW NASA

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SATELLITES THAT HAVE CAPTURED

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COMET IMAGES.

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WHAT CAN WE LEARN?

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>> SATELLITES CAN PROVIDE US

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WITH INTERESTING INFORMATION WE

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ARE NOT ABLE TO GET FROM THE

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GROUND.

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FOR EXAMPLE, WITH THE NEOWISE

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SPACECRAFT, THE ONE WE USED TO

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DISCOVER THE COMET, WE ARE ABLE

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TO DETECT CARBON MONOXIDE AND

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CARBON DIOXIDE.

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WE ARE ABLE TO GET INFORMATION

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WE WOULDN'T BE ABLE TO DO

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OTHERWISE.

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WITH OTHER SPACECRAFT SUCH AS

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HUBBLE SPACE TELESCOPE OR SOHO

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OR A FEW OTHERS, WE ARE ABLE TO

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SEE THE COMET WITHOUT THE

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EARTH'S ATMOSPHERE OBSCURING IT

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TO GET A MORE DETAILED PICTURE

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OF WHAT'S GOING ON.

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>> THAT'S INTERESTING.

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LET'S ANSWER QUESTIONS FROM

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#ASKNASA.

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SEND US YOUR QUESTIONS.

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SO ONE QUESTION WE HAVE BEEN

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GETTING FROM A LOT OF YOU IS HOW

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DO I CAPTURE COMET NEOWISE IN

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PHOTOS?

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NASA SOCIAL MEDIA SPECIALIST

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CAPTURED SOME PHOTOS LAST YEAR

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AND SHARED A FEW OF HIS TIPS.

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>> I'M BILL.

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IN MY SPARE TIME I LOVE TO TAKE

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PICTURES OF THE NIGHT SKY.

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I DO THIS USING A CAMERA MOUNTED

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TO A TRI-POD IN MANUAL MODE SO I

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CAN LEAVE THE SHUTTER OPEN TO

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LET IN LOTS OF LIGHT.

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I CAPTURED THESE IMAGES OF COMET

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NEOWISE.

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I WENT TO A LOCATION FAR FROM

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CITY LIGHTS THAT HAD A GOOD VIEW

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OF THE NORTHEAST HORIZON.

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I COULD SEE THE COMET WITH THE

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NAKED EYE.

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SO I ZOOMED IN AND EXPOSED EACH

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SHOT FOR FOUR SECONDS.

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I DID A LITTLE POST PROCESS CAN.

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HERE'S AN ORIGINAL PHOTO OUT OF

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THE CAMERA.

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I WAS ABLE TO BRIGHTEN IT AND

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CLEAN UP SOME NOISE.

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THE END RESULT WAS HOW IT LOOKED

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IN PERSON, WHICH I HAVE TO TELL

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YOU IS BEAUTIFUL.

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SO I HOPE YOU GET A CHANCE TO

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SEE COMET NEOWISE AND ALL OF THE

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OTHER WONDERS OF THE NIGHT SKY.

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>> SO WE HAVE ANOTHER QUESTION

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FROM SOCIAL MEDIA.

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TWITTER USER FRAN ASKS WILL THE

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COMMENT KEEP MOVING HIGHER AWAY

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FROM THE HORIZON EVERY NIGHT?

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WILL IT BE OVER MY HEAD AND CAN

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I SEE IT ANY TIME AFTER DARK?

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>> RIGHT NOW IT'S MOVING FROM

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THE MORNING SKY INTO THE EVENING

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SKY.

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IT WILL BE COMING UP IN THE

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EVENING SKY AS THIS NEXT WEEK OR

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TWO GO ON.

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IT'S GOING TO BE MOVING FURTHER

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FROM THE SUN AT THE SAME TIME.

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SO THERE IS A CHANCE IT COULD BE

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GETTING FAINTER OR IF THERE IS

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EXTRA ACTIVITY, IT COULD BE

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GETTING BRIGHTER.

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WE DON'T KNOW WHAT THE

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BRIGHTNESS CHANGE WILL BE OVER

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TIME.

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IT'S GOING TO BE AFTER A MONTH

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GOING TO GET FAINTER RAPIDLY.

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IT WON'T BE OVER YOUR HEAD

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UNLESS YOU ARE PRETTY FAR NORTH.

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>> OKAY.

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AND TWITTER USER BOB ASKS NOW

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THAT THE COMMENT IS MORE VISIBLE

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IN THE EVENING, WILL IT NO

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LONGER BE VISIBLE IN THE

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MORNING?

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>> YES.

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AS JOE WAS SAYING, AS THE COMET

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MOVES IN THE SOLAR SYSTEM, WE'LL

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ONLY BE ABLE TO SEE IT IN THE

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EVENING FROM AFTER A FEW DAYS

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FROM NOW.

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YOU CAN SEE FROM THIS PICTURE

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HOW IT WILL MOVE IN THE SKY AS

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THE TIME PROGRESSES.

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>> FANTASTIC.

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TWITTER USER ANDREW ASKS HOW

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FAST IS COMET NEOWISE TRAVELING

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THROUGH SPACE?

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>> AS EMILY MENTIONED, COMETS

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FOLLOW THESE ELLIPTICAL ORBITS.

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WHEN IT'S FARTHEST FROM THE SUN,

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IT'S AT A STAND STILL.

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RIGHT NOW IT'S MOVING AT AROUND

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40 MILES EVERY SECOND.

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TWICE AS FAST AS EARTH'S SPEED

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AROUND THE SUN.

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AS IT GOES FARTHER FROM THE SUN,

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IT WILL SLOW DOWN AS IT CLIMBS

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BACK UP.

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>> RICKY ASKS WHAT IS COMET

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NEOWISE'S TAIL MADE OF?

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>> RIGHT.

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SO THERE'S USUALLY TWO DIFFERENT

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COMET TAILS.

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YOU CAN SEE THE BROAD DUST TAIL

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WHICH HAS THIS PAIL YELLOW ISSUE

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GRAY COLOR AND YOU WILL ALSO SEE

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THE ION TAIL WHICH IS MADE OF

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IONIZED GASSES.

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BOTH OF THESE COME FROM THE

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COMET'S NUCLEUS THAT ARE LISTED

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OFF AS THE COMET GETS CLOSER TO

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THE SUN.

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BECAUSE THEY HAVE DIFFERENT

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COMPOSITIONS, THEY REACT

263
00:10:57,356 --> 00:10:59,258
DIFFERENTLY TO THE SOLAR

264
00:10:59,325 --> 00:11:05,231
RADIATION PRESSURE, THAT IS TO

265
00:11:05,297 --> 00:11:08,100
SAY THE SUN -- HOW THE SUN

266
00:11:08,167 --> 00:11:09,802
INTERACTS THROUGH THE PARTICLES.

267
00:11:09,869 --> 00:11:12,004
THE TWO DIFFERENT KIND OF

268
00:11:12,071 --> 00:11:13,773
PARTICLES GET SPREAD OUT.

269
00:11:13,839 --> 00:11:15,608
THE OTHER PART OF THE QUESTION

270
00:11:15,675 --> 00:11:19,045
WAS ABOUT HOW MUCH WATER IS IN A

271
00:11:19,111 --> 00:11:19,545
COMET.

272
00:11:19,612 --> 00:11:22,982
THIS COMET IS ABOUT THREE MILES

273
00:11:23,049 --> 00:11:23,315
ACROSS.

274
00:11:23,382 --> 00:11:25,251
AND MOST COMETS ON AVERAGE ARE

275
00:11:25,317 --> 00:11:28,621
ABOUT HALF WATER AND HALF DUST.

276
00:11:28,688 --> 00:11:31,957
TO A QUICK BACK OF THE ENVELOPE

277
00:11:32,024 --> 00:11:38,597
CALCULATION ON AN ACTUAL

278
00:11:38,664 --> 00:11:40,199
ENVELOPE, MY QUICK CAL LOCATION

279
00:11:40,266 --> 00:11:44,437
IS IT'S PROBABLY ABOUT

280
00:11:44,503 --> 00:11:46,072
13 MILLION OLYMPIC SWIMMING

281
00:11:46,138 --> 00:11:47,640
POOLS WORTH OF WATER, SO THAT'S

282
00:11:47,707 --> 00:11:49,608
A LOT OF WATER.

283
00:11:49,675 --> 00:11:50,643
>> THAT IS.

284
00:11:50,710 --> 00:11:57,216
THANK YOU FOR DOING THAT

285
00:11:57,283 --> 00:11:57,616
CALCULATION.

286
00:11:57,683 --> 00:12:00,820
HOW FAST CAN THE COMET BE SEEN

287
00:12:00,886 --> 00:12:02,354
MOVING TO THE HUMAN EYE?

288
00:12:02,421 --> 00:12:04,290
>> YOU CAN'T SEE IT WITH THE

289
00:12:04,356 --> 00:12:10,429
HUMAN EYE, ALTHOUGH YOU MIGHT

290
00:12:10,496 --> 00:12:12,631
NOTICE WITH THE BACKGROUND STARS

291
00:12:12,698 --> 00:12:14,567
AND YOU ARE TAKING IMAGES.

292
00:12:14,633 --> 00:12:16,502
MINUTE TO MINUTE, IT'S NOT

293
00:12:16,569 --> 00:12:16,902
MOVING FAST.

294
00:12:16,969 --> 00:12:21,841
IF YOU TAKE TWO IMAGES NIGHT TO

295
00:12:21,907 --> 00:12:23,542
NIGHT, YOU CAN SEE IT.

296
00:12:23,609 --> 00:12:25,611
YOU CAN'T SEE THAT MOTION EVEN

297
00:12:25,678 --> 00:12:29,482
OVER JUST ONE DAY.

298
00:12:29,548 --> 00:12:31,717
>> SO WE HAVE ANOTHER QUESTION

299
00:12:31,784 --> 00:12:33,486
FROM TWITTER.

300
00:12:33,552 --> 00:12:35,454
WILL I BE ABLE TO SEE IT FROM

301
00:12:35,521 --> 00:12:36,155
THE U.K.?

302
00:12:36,222 --> 00:12:38,190
>> YEAH, YOU SHOULD BE ABLE TO

303
00:12:38,257 --> 00:12:42,728
SEE IT FROM MOST PLACES IN THE

304
00:12:42,795 --> 00:12:43,429
NORTHERN HEMISPHERE AS LONG AS

305
00:12:43,496 --> 00:12:45,631
YOU HAVE A REASONABLY DARK SKY

306
00:12:45,698 --> 00:12:48,734
AND A CLEAR VIEW OF THE

307
00:12:48,801 --> 00:12:49,368
NORTHWESTERN HORIZON.

308
00:12:49,435 --> 00:12:54,974
I KNOW THAT SOME FOLKS IN THE

309
00:12:55,040 --> 00:12:57,109
NORTHERN HEMISPHERE ARE, WE ARE

310
00:12:57,176 --> 00:12:59,478
IN SUMMER, IF YOU ARE

311
00:12:59,545 --> 00:13:00,513
PARTICULARLY FAR NORTH, YOU

312
00:13:00,579 --> 00:13:03,916
DON'T GET A LOT OF DARK TIME.

313
00:13:03,983 --> 00:13:06,085
STILL TRY TO GO FOR IT, YOU NEED

314
00:13:06,152 --> 00:13:10,022
TO SEE IF THAT WOULD WORK.

315
00:13:10,089 --> 00:13:11,357
>> OKAY.

316
00:13:11,423 --> 00:13:15,027
SO WE HAVE ANOTHER QUESTION.

317
00:13:15,094 --> 00:13:20,065
THEY ASK HOW IS NEOWISE FORMED?

318
00:13:20,132 --> 00:13:24,136
>> I WILL TAKE THAT ONE.

319
00:13:24,203 --> 00:13:26,105
SO COMETS WERE FORMED IN THE

320
00:13:26,172 --> 00:13:28,374
EARLY DAYS OF OUR SOLAR SYSTEM,

321
00:13:28,440 --> 00:13:31,043
WHEN EVERYTHING WAS THIS BIG

322
00:13:31,110 --> 00:13:32,878
DISK OF GAS AND DUST, WE DIDN'T

323
00:13:32,945 --> 00:13:35,447
HAVE THE PLANETS OR ANYTHING

324
00:13:35,514 --> 00:13:35,781
FORMED.

325
00:13:35,848 --> 00:13:38,551
WE HAD THE STARS, EARLY SUN IN

326
00:13:38,617 --> 00:13:43,389
THE MIDDLE AND A BIG DISK OF GAS

327
00:13:43,455 --> 00:13:44,356
AND DUST.

328
00:13:44,423 --> 00:13:46,659
THINGS STARTED COLLECTING INTO

329
00:13:46,725 --> 00:13:49,795
WHAT BECAME THE COMETS AND THE

330
00:13:49,862 --> 00:13:53,032
ASTEROIDS AND PLANETS.

331
00:13:53,098 --> 00:13:54,233
THE ASTEROIDS STAYED IN THE

332
00:13:54,300 --> 00:13:56,302
MIDDLE OF THE SOLAR SYSTEM, MOST

333
00:13:56,368 --> 00:14:03,843
OF THE COMETS TEND TO GET FAR

334
00:14:03,909 --> 00:14:04,143
AWAY.

335
00:14:04,210 --> 00:14:04,877
LIKE A COLD STORAGE FOR MOST OF

336
00:14:04,944 --> 00:14:06,579
THE AGE OF THE SOLAR SYSTEM.

337
00:14:06,645 --> 00:14:08,414
THAT'S WHY THEY HAVE THESE ICES

338
00:14:08,480 --> 00:14:10,850
ON BOARD WHICH HELP TO FORM

339
00:14:10,916 --> 00:14:13,485
THESE TAILS YOU SEE LIKE WITH

340
00:14:13,552 --> 00:14:15,020
COMET NEOWISE.

341
00:14:15,087 --> 00:14:16,188
>> THE NUMBER ONE QUESTION WE

342
00:14:16,255 --> 00:14:18,190
ARE GETTING FROM SOCIAL MEDIA IS

343
00:14:18,257 --> 00:14:20,793
CAN I SEE IT FROM MY PART OF THE

344
00:14:20,860 --> 00:14:26,799
WORLD AND CAN YOU EXPLAIN WHERE

345
00:14:26,866 --> 00:14:29,869
COMET NEOWISE IS VISIBLE ACROSS

346
00:14:29,935 --> 00:14:30,402
THE GLOBE?

347
00:14:30,469 --> 00:14:32,571
>> IF YOU ARE IN THE NORTHERN

348
00:14:32,638 --> 00:14:37,409
HEMISPHERE, YOU CAN SEE IT.

349
00:14:37,476 --> 00:14:39,879
AS THE NEXT COUPLE DAYS

350
00:14:39,945 --> 00:14:42,882
PROGRESS, YOU WANT TO LOOK TO

351
00:14:42,948 --> 00:14:43,983
THE NORTHWEST.

352
00:14:44,049 --> 00:14:46,185
YOU CAN SEE WHERE IT WAS WITH

353
00:14:46,252 --> 00:14:48,020
RESPECT TO THE BIG DIPPER.

354
00:14:48,087 --> 00:14:50,422
SO THAT WILL BE MOVING UP AND

355
00:14:50,489 --> 00:14:52,258
THIS IMAGE TO THE LEFT A LITTLE

356
00:14:52,324 --> 00:14:52,524
BIT.

357
00:14:52,591 --> 00:14:54,126
SO GETTING MORE UNDERNEATH THE

358
00:14:54,193 --> 00:14:54,994
BIG DIPPER.

359
00:14:55,060 --> 00:14:57,096
YOU WANT TO GO OUT AROUND THE

360
00:14:57,162 --> 00:14:59,064
TIME THAT THE FIRST STARS START

361
00:14:59,131 --> 00:15:00,299
TO SHOW UP.

362
00:15:00,366 --> 00:15:02,334
YOU ARE NOT GOING TO BE ABLE TO

363
00:15:02,401 --> 00:15:04,904
SEE BEFORE THAT, IT'S ABOUT AS

364
00:15:04,970 --> 00:15:07,072
BRIGHT AS THE STARS IN THE BIG

365
00:15:07,139 --> 00:15:07,406
DIPPER.

366
00:15:07,473 --> 00:15:09,909
FIND OUT WHAT TIME YOUR LOCAL

367
00:15:09,975 --> 00:15:12,678
SUNSET IS, GO OUT ABOUT 45

368
00:15:12,745 --> 00:15:14,813
MINUTES AFTER THAT, WAIT UNTIL

369
00:15:14,880 --> 00:15:17,249
THE FIRST STARS START TO APPEAR.

370
00:15:17,316 --> 00:15:19,985
THAT'S WHEN YOU LOOK.

371
00:15:20,052 --> 00:15:23,155
>> IS IT VISIBLE FROM THE

372
00:15:23,222 --> 00:15:24,056
SOUTHERN HEMISPHERE AT ALL?

373
00:15:24,123 --> 00:15:27,092
>> UNFORTUNATELY, NO, NOT NOW.

374
00:15:27,159 --> 00:15:32,097
>> THAT'S A SHAME.

375
00:15:32,164 --> 00:15:36,402
WHAT IS THE DIAMETER OF COMET

376
00:15:36,468 --> 00:15:40,773
NEOWISE, AND IS IT AN

377
00:15:40,839 --> 00:15:43,242
INTERSTELLAR OBJECT?

378
00:15:43,309 --> 00:15:48,280
>> SO FROM OUR INITIAL DATA WITH

379
00:15:48,347 --> 00:15:50,783
THE NEOWISE SPACECRAFT, WE CAN

380
00:15:50,849 --> 00:15:54,019
MAKE A PRELIMINARY MEASUREMENT.

381
00:15:54,086 --> 00:15:57,890
IT'S ABOUT THREE MILES ACROSS OR

382
00:15:57,957 --> 00:15:59,458
5 KILOMETERS FOR OTHER FOLKS WHO

383
00:15:59,525 --> 00:16:03,062
MIGHT USE THE METRIC SYSTEM.

384
00:16:03,128 --> 00:16:05,331
IT'S NOT AN INTERSTELLAR OBJECT.

385
00:16:05,397 --> 00:16:07,533
BY WATCHING ITS MOTION, WE CAN

386
00:16:07,599 --> 00:16:10,436
SEE THAT IT'S BOUND TO THE SUN'S

387
00:16:10,502 --> 00:16:10,803
GRAVITY.

388
00:16:10,869 --> 00:16:12,905
IT'S COMING IN VERY RAPIDLY AND

389
00:16:12,972 --> 00:16:14,873
THEN IT'S GOING TO GO FAR BACK

390
00:16:14,940 --> 00:16:15,841
OUT AGAIN.

391
00:16:15,908 --> 00:16:17,710
BUT THEN IT SHOULD COME BACK

392
00:16:17,776 --> 00:16:21,513
AGAIN IN ABOUT 6,800 YEARS.

393
00:16:21,580 --> 00:16:25,718
>> FANTASTIC.

394
00:16:25,784 --> 00:16:29,188
TWITTER USER ASKS I WOULD LIKE

395
00:16:29,254 --> 00:16:31,957
TO KNOW IF COMETS HAVE REGULAR

396
00:16:32,024 --> 00:16:36,428
ORBIT, AND I WOULD LIKE TO KNOW

397
00:16:36,495 --> 00:16:37,730
IF THE FORMATION OF COMET TAILS

398
00:16:37,796 --> 00:16:40,265
LEADS TO THE REDUCTION IN THE

399
00:16:40,332 --> 00:16:40,566
MASS.

400
00:16:40,632 --> 00:16:43,502
IS IT REPLENISHED WHEN THE COMET

401
00:16:43,569 --> 00:16:45,537
IS FARTHER AWAY FROM THE SUN?

402
00:16:45,604 --> 00:16:51,243
>> COMETS DO HAVE REGULAR

403
00:16:51,310 --> 00:16:51,577
ORBITS.

404
00:16:51,643 --> 00:16:55,447
THIS IS AN ELLIPTICAL ORBIT.

405
00:16:55,514 --> 00:16:57,616
EACH TIME IT GOES AROUND THE

406
00:16:57,683 --> 00:17:00,185
SUN, IT LOSES SOME OF ITS MASS.

407
00:17:00,252 --> 00:17:02,254
THERE IS NOTHING OUT THERE TO

408
00:17:02,321 --> 00:17:02,888
REPLENISH IT.

409
00:17:02,955 --> 00:17:05,958
ALL THE GASSES AND DUST ARE NO

410
00:17:06,025 --> 00:17:07,026
LONGER THERE.

411
00:17:07,092 --> 00:17:10,562
THEY ARE BEEN BLOWN OUT BY THE

412
00:17:10,629 --> 00:17:12,231
SOLAR WIND OVER THE PAST

413
00:17:12,297 --> 00:17:13,298
BILLIONS OF YEARS.

414
00:17:13,365 --> 00:17:16,568
EACH TIME IT GOES BY, IT WILL

415
00:17:16,635 --> 00:17:19,705
LOSE A LITTLE MORE UNTIL ONE DAY

416
00:17:19,772 --> 00:17:24,209
IT DISSINTY GREATS.

417
00:17:24,276 --> 00:17:28,614
>> HOW LONG DOES THAT PROCESS

418
00:17:28,680 --> 00:17:28,914
TAKE?

419
00:17:28,981 --> 00:17:30,315
>> NO, GO AHEAD.

420
00:17:30,382 --> 00:17:34,286
>> THAT PROCESS, DEPENDS ON THE

421
00:17:34,353 --> 00:17:34,586
COMET.

422
00:17:34,653 --> 00:17:36,255
SOME LOSE MASS QUICKLY.

423
00:17:36,321 --> 00:17:37,990
IF THIS IS THE FIRST TIME IN THE

424
00:17:38,057 --> 00:17:39,425
SOLAR SYSTEM AND NOT MUCH IN THE

425
00:17:39,491 --> 00:17:41,493
WAY AND THERE IS A LOT OF ICE ON

426
00:17:41,560 --> 00:17:44,496
THE SURFACE, IT CAN LOSE THAT

427
00:17:44,563 --> 00:17:44,830
QUICKLY.

428
00:17:44,897 --> 00:17:48,033
AS IT GETS OLDER, THE ICE HAS

429
00:17:48,100 --> 00:17:50,269
BEEN BLOWN OFF AND THE DUST

430
00:17:50,335 --> 00:17:53,105
REMAINS T GETS THIS CRUST THAT

431
00:17:53,172 --> 00:17:53,639
SHIELDS IT.

432
00:17:53,705 --> 00:17:56,642
THEY ARE EXPECTED TO GET WEAKER,

433
00:17:56,708 --> 00:17:58,677
A LITTLE LESS POWERFUL IN TERMS

434
00:17:58,744 --> 00:18:00,279
OF THE AMOUNT OF MATERIAL BEING

435
00:18:00,345 --> 00:18:01,713
SHED OFF.

436
00:18:01,780 --> 00:18:03,248
THEY MIGHT STILL HAVE EYES ON

437
00:18:03,315 --> 00:18:05,818
THE SURFACE, IT'S JUST THAT

438
00:18:05,884 --> 00:18:07,953
THERE IS A THICK LAYER OF RUBBLE

439
00:18:08,020 --> 00:18:10,155
THAT PROTECTS THEM FROM THE HEAT

440
00:18:10,222 --> 00:18:14,827
OF THE SUN.

441
00:18:14,893 --> 00:18:17,729
>> KATE FROM TWITTER ASKS WHY IS

442
00:18:17,796 --> 00:18:19,932
THERE A PUBLIC CONFERENCE

443
00:18:19,998 --> 00:18:23,302
TOMORROW WHERE THE NASA DEFENSE

444
00:18:23,368 --> 00:18:23,635
OFFICES.

445
00:18:23,702 --> 00:18:25,237
WHAT ARE THE POTENTIALS RISKS

446
00:18:25,304 --> 00:18:27,973
FOR OUR PLANET?

447
00:18:28,040 --> 00:18:30,509
>> I WOULD LIKE TO TAKE THIS

448
00:18:30,576 --> 00:18:30,776
ONE.

449
00:18:30,843 --> 00:18:32,077
>> OKAY.

450
00:18:32,144 --> 00:18:36,448
>> THERE IS NO RISK.

451
00:18:36,515 --> 00:18:40,786
THIS IS THREE QUARTERS OF AN

452
00:18:40,853 --> 00:18:41,487
ATRY NO MY CAL UNIT FROM US.

453
00:18:41,553 --> 00:18:43,388
THIS IS VERY FAR AWAY FROM US.

454
00:18:43,455 --> 00:18:46,992
IT'S NOT COMING ANYWHERE NEAR

455
00:18:47,059 --> 00:18:47,259
US.

456
00:18:47,326 --> 00:18:48,527
THE REASON THE COORDINATION

457
00:18:48,594 --> 00:18:50,762
OFFICE IS HAVING A PRESS

458
00:18:50,829 --> 00:18:53,465
CONFERENCE IS BECAUSE NEOWISE IS

459
00:18:53,532 --> 00:18:55,701
UNDER THE UMBRELLA OF THE

460
00:18:55,767 --> 00:18:59,037
PLANETARY DEFENSE OFFICE.

461
00:18:59,104 --> 00:19:01,907
WE FIND ALL KINDS OF THINGS LIKE

462
00:19:01,974 --> 00:19:03,008
COMET NEOWISE.

463
00:19:03,075 --> 00:19:04,276
BECAUSE THIS IS THE OFFICE THAT

464
00:19:04,343 --> 00:19:07,112
IS ALLOWING NEOWISE TO OPERATE

465
00:19:07,179 --> 00:19:08,780
AND GIVING US OUR GUIDANCE, THEY

466
00:19:08,847 --> 00:19:10,415
ARE GOING TO BE TALKING ABOUT

467
00:19:10,482 --> 00:19:12,217
WHAT WE FOUND AND ALL THE COOL

468
00:19:12,284 --> 00:19:16,855
STUFF THAT COMES OUT OF IT.

469
00:19:16,922 --> 00:19:20,058
>> THERE IS ANOTHER QUESTION ON

470
00:19:20,125 --> 00:19:20,392
TWITTER.

471
00:19:20,459 --> 00:19:23,128
ARE THERE ANY CHANCES OF NEOWISE

472
00:19:23,195 --> 00:19:24,863
BECOMING A GREAT COMET AND

473
00:19:24,930 --> 00:19:27,366
TURNING IT EXCEPTIONALLY BRIGHT?

474
00:19:27,432 --> 00:19:30,002
IF YES, WHAT ARE THE CHANCES?

475
00:19:30,068 --> 00:19:33,705
>> SO COMETS ARE NOTORIOUSLY

476
00:19:33,772 --> 00:19:35,607
HARD TO PREDICT IN TERMS OF HOW

477
00:19:35,674 --> 00:19:36,875
GREAT THEY WILL BE.

478
00:19:36,942 --> 00:19:38,443
EVEN FOR COMETS WE HAVE SEEN

479
00:19:38,510 --> 00:19:40,045
BEFORE, THIS IS A CHALLENGE.

480
00:19:40,112 --> 00:19:42,281
BUT FOR COMET NEOWISE, THE FIRST

481
00:19:42,347 --> 00:19:44,216
TIME WE ARE SEEING IT, WE DON'T

482
00:19:44,283 --> 00:19:47,519
KNOW FOR SURE.

483
00:19:47,586 --> 00:19:49,821
BECAUSE IT'S ALREADY PASSED ITS

484
00:19:49,888 --> 00:19:51,423
CLOSEST POINT TO THE SUN, WHERE

485
00:19:51,490 --> 00:19:56,495
IT'S GOTTEN THE MOST HEAT, IT'S

486
00:19:56,562 --> 00:19:58,030
UNLIKELY TO BECOME MUCH BRIGHTER

487
00:19:58,096 --> 00:19:59,097
THAN IT IS.

488
00:19:59,164 --> 00:20:01,033
BUT THEY SURPRISE US.

489
00:20:01,099 --> 00:20:02,067
KEEP A LOOK OUT.

490
00:20:02,134 --> 00:20:04,803
WHO KNOWS, WE MIGHT SEE IT

491
00:20:04,870 --> 00:20:07,973
BECOME A GREAT COMET, BUT IT

492
00:20:08,040 --> 00:20:09,808
MIGHT FADE AWAY.

493
00:20:09,875 --> 00:20:11,577
YOU NEVER KNOW.

494
00:20:11,643 --> 00:20:13,879
>> AND WE ARE ALL IN THIS

495
00:20:13,946 --> 00:20:14,780
TOGETHER RIGHT NOW.

496
00:20:14,846 --> 00:20:19,051
>> IT'S TRUE.

497
00:20:19,117 --> 00:20:22,387
>> Facebook ASKS WHY ARE THERE

498
00:20:22,454 --> 00:20:25,257
TWO OR EVEN THREE TAILS WITH

499
00:20:25,324 --> 00:20:25,591
COMETS?

500
00:20:25,657 --> 00:20:26,858
>> YEAH.

501
00:20:26,925 --> 00:20:29,294
SO AS I EXPLAINED BEFORE, COMET

502
00:20:29,361 --> 00:20:33,665
TAILS ARE MADE UP OF DUST AND

503
00:20:33,732 --> 00:20:36,935
IONS, IONIZED GASSES.

504
00:20:37,002 --> 00:20:39,338
SO THAT BROAD TAIL YOU SEE IS

505
00:20:39,404 --> 00:20:42,207
THE DUST AND IT INTERACTS WITH

506
00:20:42,274 --> 00:20:45,344
THE SUN'S SOLAR WIND DIFFERENT

507
00:20:45,410 --> 00:20:50,082
THAN THE IONIZED GASSES.

508
00:20:50,148 --> 00:20:53,685
THE THIRD TAIL, THE SODIUM TAIL,

509
00:20:53,752 --> 00:20:55,854
YOU HAVE A COMET THAT HAS A LOT

510
00:20:55,921 --> 00:20:58,957
OF DUST AND GAS COME OFF THE

511
00:20:59,024 --> 00:20:59,291
SURFACE.

512
00:20:59,358 --> 00:21:02,127
MOST THE TIME THEY ARE TOO FAR

513
00:21:02,194 --> 00:21:04,096
OR TO FAINT TO SEE THAT THIRD

514
00:21:04,162 --> 00:21:04,396
TAIL.

515
00:21:04,463 --> 00:21:07,699
SO IT'S EXCITING WHEN WE GET A

516
00:21:07,766 --> 00:21:09,635
CHANCE TO SEE THAT THIRD TAIL.

517
00:21:09,701 --> 00:21:14,072
>> WE HAVE A COUPLE OF QUESTIONS

518
00:21:14,139 --> 00:21:16,675
ABOUT WHEN WAS THE LAST TIME

519
00:21:16,742 --> 00:21:18,710
COMET NEOWISE APPEARED OR IS

520
00:21:18,777 --> 00:21:21,380
THIS THE FIRST TIME IT'S VISITED

521
00:21:21,446 --> 00:21:21,647
US?

522
00:21:21,713 --> 00:21:26,618
>> SO, IT'S ORBITAL PERIOD IS

523
00:21:26,685 --> 00:21:29,221
AROUND 6,800, 6,900 YEARS.

524
00:21:29,288 --> 00:21:31,556
THAT WOULD MEAN IT WAS HERE LAST

525
00:21:31,623 --> 00:21:33,458
ABOUT 7,000 YEARS AGO.

526
00:21:33,525 --> 00:21:38,096
AS THE COMET IS OUT, MATERIAL IS

527
00:21:38,163 --> 00:21:40,666
KICKED OFF, THEY ARE LIKE

528
00:21:40,732 --> 00:21:42,968
THRUSTER JETS.

529
00:21:43,035 --> 00:21:44,503
SOMETIMES THEY CHANGE FROM ONE

530
00:21:44,569 --> 00:21:46,672
PASS OF THE SUN TO THE NEXT.

531
00:21:46,738 --> 00:21:52,244
WE CAN SAY IT WAS HERE AROUND

532
00:21:52,311 --> 00:21:53,045
7,000 YEARS AGO.

533
00:21:53,111 --> 00:21:55,180
WE ARE NOT SURE IF IT WAS HERE

534
00:21:55,247 --> 00:21:57,049
FROM MANY MORE PASSES BEFORE

535
00:21:57,115 --> 00:21:57,382
THAT.

536
00:21:57,449 --> 00:22:00,218
OR IF IT HAS CHANGED BECAUSE OF

537
00:22:00,285 --> 00:22:03,655
THE OUT-GASSING OF THE DUST.

538
00:22:03,722 --> 00:22:05,957
>> WHAT IS THE AVERAGE

539
00:22:06,024 --> 00:22:10,996
TEMPERATURE OF A COMET?

540
00:22:11,063 --> 00:22:15,434
>> SO COMETS ARE PRETTY COLD

541
00:22:15,500 --> 00:22:20,205
COMPARED TO WHAT WE HAVE HERE ON

542
00:22:20,272 --> 00:22:20,505
EARTH.

543
00:22:20,572 --> 00:22:22,240
THEY ARE RELATIVELY WARM

544
00:22:22,307 --> 00:22:25,377
COMPARED TO THE BACKGROUND OF

545
00:22:25,444 --> 00:22:25,677
SPACE.

546
00:22:25,744 --> 00:22:27,446
FOR AN EXACT NUMBER, I HAVE TO

547
00:22:27,512 --> 00:22:29,214
PASS IT OVER TO JOE.

548
00:22:29,281 --> 00:22:37,389
I CAN'T DO THESE CALCULATIONS ON

549
00:22:37,456 --> 00:22:38,090
MY HEAD.

550
00:22:38,156 --> 00:22:39,725
>> THE TEMPERATURE IS JUST A

551
00:22:39,791 --> 00:22:41,126
FUNCTION OF HOW FAR IT IS FROM

552
00:22:41,193 --> 00:22:43,228
THE SUN, THAT'S WHERE IT'S

553
00:22:43,295 --> 00:22:44,663
GETTING ITS HEAT FROM.

554
00:22:44,730 --> 00:22:46,264
BECAUSE THIS COMMENT IS PASSING

555
00:22:46,331 --> 00:22:48,667
ABOUT THE SAME DISTANCE FROM THE

556
00:22:48,734 --> 00:22:51,069
SUN IS, IT'S GOING TO HAVE ABOUT

557
00:22:51,136 --> 00:22:52,204
THE SAME TEMPERATURE.

558
00:22:52,270 --> 00:22:53,839
IF YOU WERE STANDING ON THE

559
00:22:53,905 --> 00:22:55,741
SURFACE, PROBABLY CLOSE TO ROOM

560
00:22:55,807 --> 00:22:56,141
TEMPERATURE.

561
00:22:56,208 --> 00:22:58,944
AS IT GOES FURTHER OUT, IT WILL

562
00:22:59,010 --> 00:22:59,711
COOL OFF.

563
00:22:59,778 --> 00:23:03,448
SO IT'S GOING TO GET LIQUID

564
00:23:03,515 --> 00:23:06,551
NITROGEN AND THEN LIQUID HELIUM

565
00:23:06,618 --> 00:23:13,425
TEMPERATURES BEFORE IT GOES OUT.

566
00:23:13,492 --> 00:23:17,496
>> YOU SAID THEY CAN CHANGE

567
00:23:17,562 --> 00:23:18,096
TRAJECTORY.

568
00:23:18,163 --> 00:23:23,268
WHEN THEY CHANGE MASS, DO THEIR

569
00:23:23,335 --> 00:23:23,869
ORBITS CHANGE?

570
00:23:23,935 --> 00:23:26,638
>> YES, ABSOLUTELY, THE ORBITS

571
00:23:26,705 --> 00:23:27,506
CAN CHANGE.

572
00:23:27,572 --> 00:23:30,442
IT DEPENDS ON WHERE THE THRUSTER

573
00:23:30,509 --> 00:23:32,210
IS COMING OUT FROM.

574
00:23:32,277 --> 00:23:35,180
WE THOUGHT OF THEM AS SNOWBALLS

575
00:23:35,247 --> 00:23:38,650
LOSING MASS EVERYWHERE.

576
00:23:38,717 --> 00:23:40,719
FROM THE MISSIONS, WE SAW IT

577
00:23:40,786 --> 00:23:43,155
CAME OUT IN THESE NARROW JETS

578
00:23:43,221 --> 00:23:45,357
FROM CERTAIN PARTS ON THE

579
00:23:45,424 --> 00:23:47,359
COMET'S SURFACE.

580
00:23:47,426 --> 00:23:48,927
THEY CAN EACH CAUSE A PUSH AND

581
00:23:48,994 --> 00:23:50,929
CAN CHANGE HOW IT SPINS OR

582
00:23:50,996 --> 00:23:53,098
CHANGE THE ORBIT AROUND THE SUN.

583
00:23:53,165 --> 00:23:55,634
IT DEPENDS ON WHERE THAT JET IS

584
00:23:55,700 --> 00:24:01,540
AND WHERE IT IS WHEN IT FIRES

585
00:24:01,606 --> 00:24:01,807
OFF.

586
00:24:01,873 --> 00:24:07,746
>> IS THIS COMET DISINTEGRATING

587
00:24:07,813 --> 00:24:10,715
AS SEEN BY SOME OF THE PHOTOS?

588
00:24:10,782 --> 00:24:12,918
>> I TOOK A LOOK AT A FEW OF

589
00:24:12,984 --> 00:24:15,720
THOSE FROM A COUPLE OF DAYS AGO.

590
00:24:15,787 --> 00:24:17,722
WHAT I THINK WE ARE SEEING IN

591
00:24:17,789 --> 00:24:19,958
THOSE IMAGES IS NOT NECESSARILY

592
00:24:20,025 --> 00:24:22,327
THE COMET BREAKING UP, BUT A

593
00:24:22,394 --> 00:24:25,030
JITTER IN THE WAY THE CAMERA IS

594
00:24:25,096 --> 00:24:25,697
SET UP.

595
00:24:25,764 --> 00:24:30,469
IF YOU HAVE A CAMERA THAT'S VERY

596
00:24:30,535 --> 00:24:32,270
STABLE, YOU WILL GET A NICE

597
00:24:32,337 --> 00:24:33,371
CLEAR PICTURE.

598
00:24:33,438 --> 00:24:35,740
IF IT SHAKES A LITTLE, IT WILL

599
00:24:35,807 --> 00:24:38,009
LOOK LIKE THE COMET IS SPLITTING

600
00:24:38,076 --> 00:24:38,276
UP.

601
00:24:38,343 --> 00:24:41,279
THIS IS A COMMON THING THAT

602
00:24:41,346 --> 00:24:43,181
PROFESSIONAL ASTRONOMERS HAVE TO

603
00:24:43,248 --> 00:24:43,949
DEAL WITH.

604
00:24:44,015 --> 00:24:46,585
IF YOU SEE A LITTLE JITTER IN

605
00:24:46,651 --> 00:24:50,489
YOUR OBJECT OR IMAGES, THAT'S

606
00:24:50,555 --> 00:24:50,822
NORMAL.

607
00:24:50,889 --> 00:24:53,024
IT MEANS THAT YOU MIGHT NEED TO

608
00:24:53,091 --> 00:24:55,260
TRY TO SECURE YOUR CAMERA A

609
00:24:55,327 --> 00:24:56,561
LITTLE MORE TIGHTLY BEFORE

610
00:24:56,628 --> 00:25:02,968
TRYING TO TAKE ANOTHER LONG

611
00:25:03,034 --> 00:25:03,335
EXPOSURE.

612
00:25:03,401 --> 00:25:06,505
>> A QUESTION FROM SOCIAL MEDIA.

613
00:25:06,571 --> 00:25:09,474
WHAT DOES THE COLOR OF NEOWISE

614
00:25:09,541 --> 00:25:11,543
GASSES TELL US ABOUT ITS

615
00:25:11,610 --> 00:25:13,144
CHEMICAL MAKEUP?

616
00:25:13,211 --> 00:25:15,180
>> EMILY, YOU CAN TAKE THIS ONE.

617
00:25:15,247 --> 00:25:18,650
>> SURE.

618
00:25:18,717 --> 00:25:23,989
YEAH, SO WE CAN USE SPECTRA TO

619
00:25:24,055 --> 00:25:26,358
HELP US UNDERSTAND THE

620
00:25:26,424 --> 00:25:28,693
COMPOSITION OF COMETS.

621
00:25:28,760 --> 00:25:31,296
BY THE COLOR OF THE LIGHT WE CAN

622
00:25:31,363 --> 00:25:33,198
TELL WHAT IT'S MADE OF WITHOUT

623
00:25:33,265 --> 00:25:34,366
HAVING TO TOUCH IT.

624
00:25:34,432 --> 00:25:37,269
WHAT WE KNOW FROM COMETS IS THAT

625
00:25:37,335 --> 00:25:39,738
GENERALLY THESE ION TAILS ARE

626
00:25:39,804 --> 00:25:44,209
MADE OF HYDROGEN CYANIDE AND A

627
00:25:44,276 --> 00:25:48,246
FEW OTHER WHAT WE CALL

628
00:25:48,313 --> 00:25:51,650
CARBON-BEARING MOLECULES.

629
00:25:51,716 --> 00:25:53,218
HYDROGEN CYANIDE IS ONE OF THE

630
00:25:53,285 --> 00:25:55,287
BIGGEST ONE.

631
00:25:55,353 --> 00:25:57,989
YOU WOULDN'T WANT TO BREATHE IT

632
00:25:58,056 --> 00:26:00,492
IN IF YOU WERE STANDING ON THE

633
00:26:00,559 --> 00:26:00,792
COMET.

634
00:26:00,859 --> 00:26:02,961
>> WE HAVE LEARNED A LOT ABOUT

635
00:26:03,028 --> 00:26:04,229
COMMENT NEOWISE TODAY.

636
00:26:04,296 --> 00:26:05,897
THANK YOU FOR JOINING US.

637
00:26:05,964 --> 00:26:07,566
>> YOU ARE VERY WELL COME.

638
00:26:07,632 --> 00:26:10,302
>> YES, A LOT OF FUN.

639
00:26:10,368 --> 00:26:12,003
>> AND THANK YOU FOR JOINING US

640
00:26:12,070 --> 00:26:12,537
FROM HOME.

641
00:26:12,604 --> 00:26:15,173
IF YOU WITH A TONIGHT LEARN MORE

642
00:26:15,240 --> 00:26:20,211
OR TAKE A CLOSER LOOK AT VIEWING

643
00:26:20,278 --> 00:26:25,150
TIPS, VISIT GO.NASA.GOV.

644
00:26:25,216 --> 00:26:26,885
WE'LL END WITH A VIDEO ABOUT

645
00:26:26,952 --> 00:26:29,220
WHAT YOU NEED TO KNOW ABOUT

646
00:26:29,287 --> 00:26:32,257
NEAR-EARTH OBJECTS AND NASA'S

647
00:26:32,324 --> 00:26:34,025
MISSION TO MONITOR THEM.

648
00:26:34,092 --> 00:26:36,661
UNTIL NEXT TIME, HAPPY SKY

649
00:26:36,728 --> 00:26:44,803
WATCHING.

650
00:26:50,175 --> 00:27:07,525
♪