Where is the edge of space?

00:16:06
https://www.youtube.com/watch?v=nILOHp79njQ

Summary

TLDRThe Kármán line, presently recognized at 100 kilometers above the Earth's surface, is internationally adopted as the edge of space. However, its definition is not legally fixed and is considered questionable by scientific standards, as the atmosphere doesn't have a firm boundary. The recent paper by astrophysicist Jonathan McDowell reviews this definition and suggests the boundary could lie between 70 to 90 kilometers. McDowell's work points out that many satellites orbit below the Kármán line's traditional height, challenging its scientific validity. The line's definition holds significance beyond scientific curiosity, influencing military, economic, and tourism interests. NASA acknowledges 80 kilometers as the threshold for astronaut status, coined by the U.S., mainly for practical space exploration experiences, like weightlessness and viewing Earth. These discussions reveal how close space is, as cities are often closer to space than to their neighboring urban areas. McDowell's findings encourage a more precise understanding of where space begins, accommodating advancements in space tourism and legislation.

Takeaways

  • 🚀 The Kármán line is set at 100 km above Earth but is debated scientifically.
  • 🛰️ Many satellites orbit below the traditional Kármán line, challenging its accuracy.
  • 🧑‍🚀 NASA considers space at 80 km, awarding astronaut status over this line.
  • 📏 Jonathan McDowell suggests 70-90 km as a more accurate boundary.
  • 📊 The atmosphere doesn't have a definitive edge, complicating the boundary of space.
  • 🌐 A defined space boundary is significant for political and economic reasons.
  • 🛩️ The line’s definition affects space tourism, allowing companies to claim space travel.
  • 🌍 Realizing how space is closer than many neighboring cities is enlightening.
  • 💼 Legal space definitions impact defense strategies and international treaties.
  • 🔭 The debate encourages precise scientific re-evaluation of where space begins.

Timeline

  • 00:00:00 - 00:05:00

    The traditional definition for the beginning of outer space, known as the Karman line, is set at 100 kilometers above Earth's surface but doesn't legally define space. The definition, adopted by the Federation Internationale Aeronautique, is largely unsatisfactory as it doesn't consider the continuous nature of the atmosphere, which lacks rigid edges and varies with time and conditions. Astrophysicist Jonathan McDowell questions this definition, suggesting that aeronautical forces dissipate at altitudes below the Karman line, indicating a need to revisit this definition.

  • 00:05:00 - 00:10:00

    A new paper suggests that atmospheric drag forces on satellites indicate that the actual boundary of space could be between 70 to 90 kilometers. Various atmospheric factors and the historical idea that 100 kilometers marks the edge of where aerodynamic and gravitational forces meet are revisited. The paper highlights that many satellites have been observed to pass below 100 kilometers without leaving orbit, implying the 100-kilometer marker might not be scientifically accurate, suggesting a scientifically sound lower boundary like the mesopause around 85 kilometers.

  • 00:10:00 - 00:16:06

    Discusses the interest of multiple entities in defining where space begins. For scientific, economic, and defense purposes, the lack of a legal boundary presents challenges. The debate impacts sectors like military operations and commercial space tourism, where companies prefer a lower boundary to claim they reach space, such as NASA's 80 kilometers threshold assessed for issuing astronaut wings. The importance of a revised definition for strategic operations and commercial interests comes across strongly as the discussion about enriching human spaceflight perspectives enlarges to include economic and scientific dimensions at various altitudes.

Mind Map

Video Q&A

  • What is the Kármán line?

    The Kármán line is traditionally set at 100 kilometers above Earth, marking the boundary of space.

  • Who proposed the reassessment of the Kármán line?

    Astrophysicist Jonathan McDowell of the Harvard Smithsonian Center for Astrophysics proposed a reassessment.

  • What height does Jonathan McDowell suggest could define space?

    McDowell suggests a range between 70 to 90 kilometers might be more scientifically accurate for the boundary of space.

  • Why is the Kármán line considered problematic?

    The line at 100 kilometers is arbitrary because the atmosphere doesn't have a rigid edge, and scientific observations suggest satellites can orbit below this threshold.

  • Does the definition of the edge of space have legal implications?

    Yes, a legal definition of space is debated because it impacts economic, political, and defense considerations.

  • How does NASA define the boundary of space for astronauts?

    NASA awards astronaut wings for missions reaching above 80 kilometers (50 miles).

  • What altitude is considered for space tourism?

    Space tourism companies would prefer a lower boundary, like 80 kilometers, to feasibly sell space experiences.

  • What is the height of the Hubble Space Telescope's orbit?

    The Hubble Space Telescope orbits at an altitude of 540 kilometers above Earth.

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  • 00:00:00
    for quite a long time the sort of
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    adopted agreed definition for the edge
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    of space has been something called the
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    carmen line
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    which is located at 100 kilometers above
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    the earth's surface it is not a legal
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    definition but it's a definition that's
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    been adopted by the federation
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    international aeronautic which is the
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    world air sports federation but it's
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    it's a largely unsatisfying definition
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    because of course the atmosphere doesn't
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    have an edge it's a continuous
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    fluid body it has lots of different
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    properties in lots of different regions
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    but none of them have rigidly defined
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    edges and in fact the properties change
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    as a function of time and solar activity
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    and lots of other things 100 seems
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    almost too perfect doesn't it it does so
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    recently a paper's been published called
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    the edge of space revisiting the carmen
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    line and this was work done by an
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    astrophysicist named jonathan mcdowell
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    at the harvard smithsonian center for
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    astrophysics and he takes a closer look
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    into whether there is a real scientific
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    definition for the karman line the
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    original carmen line definition was
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    roughly associated with the idea that
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    there's a boundary between
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    where aeronautical forces stop and you
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    no longer get lift in the atmosphere
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    aeronautical lift is a mechanical force
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    it's generated by contact with the fluid
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    the fluid obviously being the atmosphere
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    and if you run out of fluid you run out
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    of force and so at the carbon line it
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    you're you're sort of where an aircraft
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    would have to travel at a speed that's
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    greater than the orbital velocity
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    in order to get enough lift from its
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    wings to stay in the air so in this
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    paper we looked at the orbits of 43 000
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    satellites have been tracked over the
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    years and of course most of them are way
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    above the karman line but there were
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    substantial numbers that throughout
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    their orbit would pass below the 100
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    kilometer line getting even closer to 80
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    kilometers and not just on their last
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    orbit before they disintegrated but they
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    had multiple passages this low and so
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    right away you can say okay well the 100
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    kilometer line doesn't make a lot of
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    sense you can't have a satellite in
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    orbit and then it comes in and oh for a
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    little bit it's not in space and then it
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    goes back into space and and on and on
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    and on and so right there is some
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    evidence to at least support the idea of
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    revisiting this definition so the second
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    thing he did was actually use an
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    atmospheric model and actually make the
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    calculations of for a typical satellite
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    where would the drag forces
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    um be enough to sort of cause it to fall
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    back to earth so like the death zone
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    the death stone for satellites that's
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    exactly it so the conclusion he makes is
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    that for a typical kind of space vehicle
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    the gravity will exceed the aerodynamic
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    forces for any object in steady flight
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    at that altitude that altitude lies in
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    about the 70 to 90 kilometer range so he
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    factors in the time variation and all of
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    this stuff and and finds a range for
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    this limit but notes that it's always
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    well below that 100 kilometer line this
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    is just one argument other arguments
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    would look at the structure of the
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    atmosphere which is quite complicated
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    but again it's divided into specific
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    layers
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    mostly
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    based on where the gradient in
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    temperature changes these are called
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    pauses and so at about 85 kilometers
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    we've got the mesopause which is the
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    boundary between the mesosphere and the
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    thermosphere and that marks the point
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    which is the coldest point in the
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    atmosphere below that point
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    the chemical pump position of the
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    atmosphere is mostly steady and above
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    that you've got different molecules
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    moving in different ways and so from
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    atmospheric physics there's also a
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    boundary more towards the 80 kilometer
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    line so what's really interesting about
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    this argument is to actually appreciate
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    how close space is because 80 kilometers
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    100 kilometers that's not that far away
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    you can easily drive that in an hour
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    so i thought it might be fun to look on
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    a map and actually appreciate um to
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    scale how how how far away space is of
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    course our map is centered on the center
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    of the universe which is here in
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    nottingham and the unit that we're going
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    to use to mark scale on this map
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    is the humble lego block the height of
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    this brick is 3.2 millimeters and so
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    i've printed this map so that five of
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    these lego bricks
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    represent 100 kilometers on this map to
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    put some things into scale first let's
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    talk about airliners so when we're on a
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    commercial airliner we're traveling at
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    about an altitude of 10 to 12 kilometers
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    so when we're traveling on a commercial
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    airline we're not even traveling at the
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    height of this brick above this map so
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    the next scale i'm going to show you is
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    the world record for how high a human
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    being has jumped out of a balloon to
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    skydive down to earth so this record was
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    broken recently by alan eustis
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    and he jumped from a height of 41
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    kilometers so that would represent two
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    bricks on this map and so now we want to
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    go up to the karman line and so the
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    debate we're discussing today is whether
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    we define the edge of space at 80
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    kilometers which is here
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    or 100 kilometers which is
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    here doesn't seem that hard anyway does
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    it so i think that's the amazing thing
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    uh to appreciate so if this height is a
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    hundred kilometers what's really amazing
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    is how small this number actually is how
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    close we are to space so if i tip this
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    on this the edge and i've got 100
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    kilometer marker here you can see that
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    nottingham is closer to space than it is
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    to london and i can get that london in
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    an hour and a half on the train all
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    right so maybe nottingham to london
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    doesn't mean very much to you but if you
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    you're in new york you're closer to
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    space than you are to philadelphia
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    if you're in los angeles you're closer
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    to space than you are to san diego oh
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    let me do a canadian one okay
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    if you're in montreal you're closer to
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    space than you are to ottawa
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    i've got no idea where those places are
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    all right cool i looked up adelaide for
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    you but nothing's near adelaide so it
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    didn't work when do you become an
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    astronaut so
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    nasa gives its astronaut wings to anyone
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    who's trained and flown a successful
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    mission that reaches above 50 miles
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    which is 80 kilometers so that's
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    actually the lower limit and there's a
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    similar acknowledgement from the us
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    for civilians who have piloted a
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    successful flight above that line is
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    this important like is this just a bunch
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    of people writing papers or does it
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    matter where space starts and finishes
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    so
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    it it matters from a scientific
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    perspective because scientists like to
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    study these sorts of things so it's
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    perfectly understandable that people who
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    are interested in
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    atmospheric physics and the orbits of
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    satellites would care but it it actually
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    does have some wider issues that now
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    touch on issues of economics and
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    politics and defense and things like
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    that
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    so i mentioned there is no international
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    agreed legal definition of space there
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    have been for some time moves to make a
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    legal definition
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    but that's always been opposed by the
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    u.s
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    and you can understand why because from
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    a military point of view a government
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    wouldn't want to be restricted by
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    international space treaties
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    when it's trying to launch high altitude
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    ballistic missiles something like that
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    and what about space tourism i guess
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    they want it to be as low as possible so
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    they can sell their space flights well
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    that's the other issue so commercial
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    space tourism is becoming a thing now as
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    we film this virgin galactic has just
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    managed to pilot a vehicle to 82
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    kilometers by the nasa definition that
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    counts as entering space by the fai
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    definition it doesn't because they
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    haven't reached the karman line but it
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    would matter very very much to a
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    commercial enterprise to be able to
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    say that they can take people into space
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    now practically speaking
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    you know i think what you would want
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    from a space mission is the experience
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    of weightlessness and the experience of
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    looking out the window and seeing the
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    earth as a as a ball you would get that
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    from 80 kilometers as well as you would
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    from 100 kilometers but like i look at
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    that and i look at how low that is and i
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    imagine how come you can see the
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    curvature of the earth from such a that
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    doesn't seem that high i think partly
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    that's because i've printed a map out on
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    a flat piece of paper so in reality this
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    is a curved surface that i'm showing you
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    here you might not see it as a complete
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    ball but you would definitely see the
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    curvature of the earth you would
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    experience the earth as a sphere it
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    becomes
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    quite clear that for commercial
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    enterprise you're not going to want to
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    waste money and fuel and
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    increase risk by taking people up to 100
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    kilometers if they can get the same
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    experience going to 80 kilometers
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    but part of that experience for people
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    will be able will be being able to say i
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    have officially been to space where
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    would you be drawing the line well i'm
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    pretty convinced by this paper i mean it
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    has some pretty sound arguments from a
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    number of different directions so i
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    think if there was a move to redefine
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    the 80 kilometer line as the mcdowell
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    line i think that should go down very
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    well but but mcdowell says 70 to 90.
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    that's like super vague
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    well that's just because scientists you
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    you know scientists you've talked to
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    enough of us over the years and we like
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    our arab bars and we like our confidence
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    intervals but if you want to define a
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    line you might as well put it in the
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    middle of a region that is well-bounded
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    this paper has revisited the numbers and
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    the back of the envelope calculations
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    that gave 100
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    are now refined and they might not give
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    a more precise number but they at least
  • 00:09:48
    show us that it's not a hundred and so
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    it's
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    very unsatisfying to keep it at that
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    level i thought it would be fun to
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    actually build up a perspective on the
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    altitude that other objects in space get
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    part of this was motivated by the fact
  • 00:10:03
    that just last week i went outside as i
  • 00:10:05
    was coming home from work and happened
  • 00:10:07
    to see the international space station
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    go overhead it was really bright it was
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    a beautiful passage and as always i was
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    struck by looking up and thinking
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    oh my god there's human beings flying
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    above my head in orbit around the earth
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    that's pretty amazing how far away are
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    they actually up there the space shuttle
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    now no longer in existence but i
  • 00:10:25
    couldn't resist getting my lego out i
  • 00:10:27
    used to take astronauts up to the
  • 00:10:29
    international space station like may
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    jameson and that's at 400 kilometers
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    above the surface of the earth
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    so in
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    our lego bricks if this is a hundred we
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    need four times that amount
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    so
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    let's
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    do this 13
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    14
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    16 i feel like i'm on lego masters
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    20. excellent right so this is the orbit
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    at which human beings continuously
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    inhabit a space station orbiting the
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    earth
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    and even that is not that high i'm
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    slightly less impressed
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    that wasn't your goal was it
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    i think one of the values of human space
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    flight one of the real values is
  • 00:11:14
    cultural not scientific
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    and it's putting human beings high
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    enough to give them that perspective on
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    space
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    and if they only have to go that high
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    to be able to look out in one direction
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    and see nothing but the infinity of
  • 00:11:30
    space and then turn around and look down
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    and see the earth
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    in
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    enough scope
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    to see
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    not borders and not resources to be
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    exploited but to appreciate that this is
  • 00:11:43
    the one and only place where life in the
  • 00:11:46
    universe exists and to look out to the
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    horizon and appreciate
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    how razor thin that precious atmosphere
  • 00:11:53
    that keeps us safe is
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    then i think i think it's quite amazing
  • 00:11:57
    that you don't have to get that high up
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    to find a perspective where you realize
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    just how precarious and how delicate the
  • 00:12:05
    ecosystem and the geosystem on earth is
  • 00:12:10
    what else you want to show me you got
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    hubble there or okay so i've got uh
  • 00:12:14
    nancy roman and the hubble space
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    telescope one of my favorites
  • 00:12:17
    and this orbits at an altitude of 540
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    kilometers it used to be higher but it's
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    slowly even at that altitude it suffers
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    from accumulative
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    atmospheric drag over time so it's going
  • 00:12:29
    lower and lower and that represents
  • 00:12:32
    pretty much the highest altitude that
  • 00:12:34
    the space shuttle could reach because it
  • 00:12:36
    was hubble was designed to be put into
  • 00:12:39
    earth orbit at an altitude where the
  • 00:12:41
    space shuttle could repeatedly go and
  • 00:12:43
    service it and it's a good thing it did
  • 00:12:45
    because we benefited from those
  • 00:12:47
    servicing missions quite a lot and so
  • 00:12:49
    i've got 20 bricks now and i need to put
  • 00:12:52
    eight more to get up to the height of
  • 00:12:55
    the hubble space telescope so
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    one
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    two
  • 00:13:02
    three
  • 00:13:03
    five
  • 00:13:06
    now we've run out of thin bricks so
  • 00:13:08
    we're gonna put
  • 00:13:10
    three more on top and so that's how high
  • 00:13:13
    the hubble space telescope is
  • 00:13:15
    all right so there's the hubble space
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    telescope yeah there you go success not
  • 00:13:20
    to scale of course the whole space
  • 00:13:21
    telescope is about the size of the bus
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    not about the width of the united
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    kingdom what's higher than that well
  • 00:13:26
    there's lots of satellites up there in
  • 00:13:27
    orbit gps global positioning satellites
  • 00:13:30
    orbit at an altitude of 20 000
  • 00:13:33
    kilometers above the surface of the
  • 00:13:35
    earth that would require a thousand lego
  • 00:13:37
    bricks and i'm not going to build that
  • 00:13:39
    today
  • 00:13:40
    but i would just note that that would
  • 00:13:42
    take us 3.2 meters
  • 00:13:44
    above this map
  • 00:13:46
    okay so right through the ceiling up
  • 00:13:48
    there somewhere okay and these are
  • 00:13:49
    satellites they're in geosynchronous
  • 00:13:51
    orbits so they orbit the earth twice a
  • 00:13:53
    day but there are satellites that are
  • 00:13:55
    even further up they're called
  • 00:13:56
    geostationary orbits their orbital
  • 00:13:58
    period is matched with the rotation of
  • 00:14:00
    the earth so they orbit once a day which
  • 00:14:02
    means that they are effectively always
  • 00:14:05
    above the same location
  • 00:14:07
    above the equator and these are the
  • 00:14:09
    satellites that give us our weather meet
  • 00:14:11
    readings and our active our
  • 00:14:14
    communications relays on this scale
  • 00:14:16
    you'd need
  • 00:14:17
    1789 bricks which would take you 5.7
  • 00:14:20
    meters above
  • 00:14:21
    the table
  • 00:14:22
    all right well that's way up way up
  • 00:14:24
    we're looking here down at the uk and
  • 00:14:26
    europe how many bricks down is the other
  • 00:14:29
    side of the earth so i said that the gps
  • 00:14:32
    satellites are at a thousand bricks
  • 00:14:34
    above the earth um but the other side of
  • 00:14:36
    the earth would only be 640 bricks so
  • 00:14:39
    that's less than the height of the gps
  • 00:14:41
    satellites what about what if i wanted
  • 00:14:42
    to go to the moon of course you want to
  • 00:14:44
    go to the moon well you would need to
  • 00:14:45
    travel 19
  • 00:14:47
    220
  • 00:14:48
    lego bricks away which on this scale
  • 00:14:51
    would be 60 meters there's been enough
  • 00:14:53
    recent attention to this idea that the
  • 00:14:56
    karmann line needs to be redefined that
  • 00:14:58
    the organizations that deal with
  • 00:15:00
    aeronautical things and the organization
  • 00:15:02
    that deals with astronautical things are
  • 00:15:05
    proposing to get together in the coming
  • 00:15:07
    year to have a symposium to look at the
  • 00:15:09
    scientific and the political and
  • 00:15:12
    whatever other arguments go into this to
  • 00:15:14
    see if we need to actually have a
  • 00:15:16
    definition of where is space and what
  • 00:15:18
    that might be we made a video a couple
  • 00:15:20
    years ago saying voyagers left the solar
  • 00:15:22
    system and just left the solar system
  • 00:15:23
    again so most things in space don't have
  • 00:15:26
    a hard edge and that means that
  • 00:15:28
    different definitions can apply
  • 00:15:31
    and you can argue to until the cows come
  • 00:15:33
    home about whether pluto's a planet or
  • 00:15:35
    where the solar system ends or how big
  • 00:15:38
    is the milky way and to some extent you
  • 00:15:40
    will never get a satisfying answer
  • 00:15:42
    because
  • 00:15:43
    science often comes with caveats that
  • 00:15:45
    say it depends what you mean
  • 00:15:50
    i can tilt it but you'll notice that the
  • 00:15:52
    axis of the spin keeps pointing the same
  • 00:15:56
    direction it explains things but the
  • 00:15:57
    main thing it does is creates a huge
  • 00:15:59
    problem
  • 00:16:00
    because if you're a theoretical
  • 00:16:01
    physicist you can do a calculation that
  • 00:16:02
    says okay so i'm creating all these
  • 00:16:04
    virtual particles
Tags
  • Kármán line
  • space boundary
  • Jonathan McDowell
  • atmospheric physics
  • aeronautics
  • satellite orbits
  • space tourism
  • NASA