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between the earth and the sun we tend to

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imagine empty space

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but every day

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every moment solar forces fill the void

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the grey mesh you see here is the

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magnetosphere it's effectively a bubble

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around the earth created by our planet's

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magnetic field squashed and elongated as

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intensely energized solar particles

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collide with it without the

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magnetosphere life on earth would likely

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cease

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naturally we want to know more about it

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so let's start close to home

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these near-earth satellites monitor

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solar activity interactions with our

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planet's atmosphere and other aspects of

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the sun's condition

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you'll notice how they orbit the earth

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quickly about once every 90 minutes or

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so

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remember this because the rate of times

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passage will change as we move through

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the solar system

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further away we see satellites measuring

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the three-dimensional boundaries of the

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magnetosphere as it interacts with the

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solar wind

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and let's be clear this is more than an

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academic exercise nasa's fleet of

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research satellites gathers vital

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information

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solar phenomena can jeopardize

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astronauts and provoke dramatic

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challenges to communications systems and

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the electrical grid on the ground

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time speeds up as we move out

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more space between objects means we have

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to travel greater distances and our tour

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of the heliosphere only lasts a few

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minutes

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while we're traveling take note of

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something you might not have considered

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before

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not all orbits look the same

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in close satellite paths essentially

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circle the earth

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but farther away we begin to encounter a

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wider variety of orbits designed for

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varying purposes

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the cluster vehicles are on a high

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elliptical flight path

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geotail makes a lazy loop all alone

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the two stereo satellites fly in

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relatively close formation but they

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won't stay that way for long

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i'll show you how in a moment but the

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point is navigation out here is harder

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than it looks a vehicle can't simply fly

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from place to place but for some

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missions like stereo precise position

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makes all the difference

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why

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the two stereo satellites will deliver

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3d pictures of the sun similar to the

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way your two eyes perceive 3d

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remember i said to keep an eye on

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stereo's flight path

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watch as one of the two stereo vehicles

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intercepts the moon's orbit a second

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time

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here it comes

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as they close the distance the

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spacecraft uses the moon's gravity to

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execute a cool maneuver like a roller

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coaster zooming up and into a corkscrew

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just after hitting a big drop

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now the vehicles are headed to their

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final orbits

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tight loops around the earth loose

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orbits out into space bank shots off the

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moon there are many ways to travel from

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place to place but sometimes travel is

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not the goal sometimes it pays to park

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welcome to a lagrange point

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this one l1 in space speak denotes a

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relative position between the earth and

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the sun where the gravitational pull of

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each object is in approximate balance

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these so-called halo orbits around l1

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make good places for hovering spacecraft

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to take observations of either the earth

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or sun

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we find a number of observatories

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patrolling out here

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including an extremely famous and

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extremely successful solar observatory

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called soho

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notice how l1 exists well in front of

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the magnetosphere

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this part of the solar system is fully

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bathed in the solar wind without the

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protection of earth's magnetic shield

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therefore it's extremely useful for

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studying solar activity without

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let's briefly revisit the area around

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the earth simulated time slows again as

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the distance between objects shrinks

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but as we once again approach our home

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you'll notice the calendar has advanced

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two years

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new satellites have entered the dance

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including the five themis vehicles

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the near-earth fleet of satellites

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swarms like bees around a hive some

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ranging out beyond the magnetosphere

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somewhere inside

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it's provocative to consider that all

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this activity takes place in space

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something we generally perceive as empty

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but what we find instead from light to

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charged particles to magnetic fields

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demonstrates a strange and wonderful

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solar vitality

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in fact there's a particular scientific

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discipline that describes the study of

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these things

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it's heliophysics from the greek word

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for sun combined with the word used to

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describe the study of matter and energy

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heliophysics studies how the sun's

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sphere of influence interacts with

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planets and the interstellar medium the

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barely tangible stuff that fills what we

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typically regard as empty space

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almost done but we've got to get moving

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if we're going to see the full extent of

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the sun's influence

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pulling way way back earth's

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magnetosphere effectively disappears

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almost all of our solar observing fleet

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shrinks like boats on the horizon

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almost

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but not all

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two legendary spacecraft voyager 1 and 2

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are out there still taking measurements

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notice the gravity assist bank shots and

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their flight paths

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launched in 1977 the voyager spacecraft

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are the most distant artifacts humanity

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has ever cast out into space

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time capsules from a small blue planet

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they are also the first human objects to

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encounter the sun's termination shock

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the area where the solar wind slows down

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enough to be affected by the flow of

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interstellar particles

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in a couple of decades one of the

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voyager crafts should pass the

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heliopause the zone where the sun's

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influence meets the interstellar medium

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years later it should encounter the

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so-called bow shock that's the wake and

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flowing interstellar particles as they

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move around the bubble of energy and

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particles emanating from our star

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our star the sun

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neither particularly large nor powerful

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as stars go stretches itself out further

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than even our most distant probes

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as we discover how to coexist with our

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own solar dynamo we stretch our