1. Subscribersonhouse
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    10 Sep '15 22:41
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    This is a link to a woman physicist who wrote the Earth's magnetic field at 8 E10 gauss, 80 billion gauss.

    The question is, we know we feel a field of around a gauss or so here on earth so where does that figure she writes come from?

    My guess is it is the sum total of all the field lines in Earth's magnetic field but is that right?
  2. Standard memberDeepThought
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    11 Sep '15 01:25
    Originally posted by sonhouse
    https://www.youtube.com/watch?v=KcW8XSuNZzg

    This is a link to a woman physicist who wrote the Earth's magnetic field at 8 E10 gauss, 80 billion gauss.

    The question is, we know we feel a field of around a gauss or so here on earth so where does that figure she writes come from?

    My guess is it is the sum total of all the field lines in Earth's magnetic field but is that right?
    No the cgs unit gauss is a measure of flux per unit area, in other words the field strength, so the total flux is probably not what she calculated, I haven't watched the video. The Earth's magnetic field is generated by a natural dynamo effect from the inner core, she's probably referring to the field strength around the core, the 5000 km of material in the way may explain the attenuation; but frankly I'm skeptical about that 8E10 gauss figure, it sounds way too high.
  3. Subscribersonhouse
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    11 Sep '15 02:141 edit
    Originally posted by DeepThought
    No the cgs unit gauss is a measure of flux per unit area, in other words the field strength, so the total flux is probably not what she calculated, I haven't watched the video. The Earth's magnetic field is generated by a natural dynamo effect from the inner core, she's probably referring to the field strength around the core, the 5000 km of material in ...[text shortened]... the attenuation; but frankly I'm skeptical about that 8E10 gauss figure, it sounds way too high.
    Watch the vid, she writes the numbers quite clearly on a screen. Goes on to say the relative strength of the other planets, like Jupiter coming in thousands of times the strength of Earth. If that was the case, wouldn't a metallic object in orbit around Jupiter be pulled in by gravity AND magnetic energy too? I mean, if the measured strength of Earth's field is around a half a gauss, then the measured field of Jupiter would be thousands of gauss and that is a pretty strong field, enough to pick up cars in a junk yard magnet system. Seems that would effect the orbit of iron bearing rocks, what do you think? She lists Jupiter as almost 20 THOUSAND times the strength of Earth's field. That would be, using her numbers, about 1.5 E15 gauss. But 20,000 times ours means the field you feel would still be 10,000 gauss at least. How could an iron object stay in orbit with that kind of field?
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    11 Sep '15 12:55
    Well according to Wikipedia the Earth's magnetic field is 0.25~0.60 gauss at the surface
    and 25 gauss in the core...

    https://en.wikipedia.org/wiki/Gauss_%28unit%29

    And 1E(12~13) gauss is the field strength of a neutron star...

    I am struggling to work out where the hell you would get a number like 8E10 from.

    She goes on to say that Jupiter has a magnetic field 19,519 times stronger than the Earth's [bit of superfluous
    precision there] ... When according to wiki, Jupiter has a magnetic field that is an order of mag larger than the Earth's...
    ~4.28 gauss, or ~10 times the Earth's....

    https://en.wikipedia.org/wiki/Magnetosphere_of_Jupiter

    However the Magnetic Moment is ~18,000 times larger... which looks kinda similar to her 19,500 number...
    I wonder if she is talking about magnetic moments?

    Except that magnetic moments don't have the unit of gauss...

    She seems to be a genuine astrophysicist, and this seems to be an epically big mistake to make for something
    you are publicising...

    I just can't see what we're missing.
  5. Subscribersonhouse
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    11 Sep '15 13:40
    Originally posted by googlefudge
    Well according to Wikipedia the Earth's magnetic field is 0.25~0.60 gauss at the surface
    and 25 gauss in the core...

    https://en.wikipedia.org/wiki/Gauss_%28unit%29

    And 1E(12~13) gauss is the field strength of a neutron star...

    I am struggling to work out where the hell you would get a number like 8E10 from.

    She goes on to say that Jupiter ha ...[text shortened]... g mistake to make for something
    you are publicising...

    I just can't see what we're missing.
    Same here. You could see the problems of magnetically sensitive materials in orbit around a planet with a 10,000 gauss magnetic field! It would not be in orbit very long since that would outclass gravity thousands to one! I hope I can email her and have her explain the terms better. What is magnetic moment?
  6. Standard memberDeepThought
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    11 Sep '15 17:21
    Originally posted by googlefudge
    Well according to Wikipedia the Earth's magnetic field is 0.25~0.60 gauss at the surface
    and 25 gauss in the core...

    https://en.wikipedia.org/wiki/Gauss_%28unit%29

    And 1E(12~13) gauss is the field strength of a neutron star...

    I am struggling to work out where the hell you would get a number like 8E10 from.

    She goes on to say that Jupiter ha ...[text shortened]... g mistake to make for something
    you are publicising...

    I just can't see what we're missing.
    I did a quick google search, she's at UCLA and is a graduate student according to their website. So I think this is to do with astrophysicists using strange units, bear in mind this is a bunch of people who thing that any element with a proton number bigger than 2 is a metal. I copied your check on Wikipedia for Saturn, it gives the magnetic field strength as slightly weaker than Earth's and its magnetic moment as "about 580 times larger [than Earth's]".

    She gives the magnetic moment as 8E10 "gauss". The radius of the Earth is 6370 km, and if we find the cube of that then it is 25.85 E10, so we can get her figure by dividing a surface field of 0.3 gauss by the cube of the radius of the Earth in kilometres. So it looks like her units are gauss/km^3.
  7. Subscribersonhouse
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    11 Sep '15 18:05
    Originally posted by DeepThought
    I did a quick google search, she's at UCLA and is a graduate student according to their website. So I think this is to do with astrophysicists using strange units, bear in mind this is a bunch of people who thing that any element with a proton number bigger than 2 is a metal. I copied your check on Wikipedia for Saturn, it gives the magnetic field stre ...[text shortened]... y the cube of the radius of the Earth in kilometres. So it looks like her units are gauss/km^3.
    It would have been nice if she had said that in the video.
  8. Standard memberDeepThought
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    11 Sep '15 18:55
    Originally posted by sonhouse
    It would have been nice if she had said that in the video.
    By graduate student standards it's a paragon of clarity. She's probably used to relative units and tripped up a bit at the start because the point she wanted to make just used the relative units, which was the part she spent most time on. Based on her supervisor's primary research interest (plasma physics using lasers) she's probably looking at some aspect of relativistic jets or natural astronomical free electron lasers and uses specialized units.
  9. Subscribersonhouse
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    12 Sep '15 10:02
    Originally posted by DeepThought
    By graduate student standards it's a paragon of clarity. She's probably used to relative units and tripped up a bit at the start because the point she wanted to make just used the relative units, which was the part she spent most time on. Based on her supervisor's primary research interest (plasma physics using lasers) she's probably looking at some as ...[text shortened]... ct of relativistic jets or natural astronomical free electron lasers and uses specialized units.
    Ah, like those lasers used to kickstart electron acceleration, making tabletop accelerators with gigavolt acceleration and more.
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