Magnetic north??? Magnetic north pole???

Discussion in 'Earth Science' started by kingwinner, Sep 18, 2005.

  1. kingwinner Registered Senior Member

    Messages:
    796
    I found myself confused with the terms of magnetic north and magnetic north pole...I found many definitions from the web and the following are my understandings, please point it out if I am wrong, thank you!

    -The magnetic north is in the southern hemisphere in the present time
    -The magnetic north pole, or north magnetic pole, is in the northern hemisphere now
    -The magnetic north is the magnetic south pole and vice versa
    -The geomagnetic north pole and the north magnetic pole are the same thing
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. Light Registered Senior Member

    Messages:
    2,258
    Hi, Kingwinner,

    Yes, I'd seen some of the stuff on the web and the way it's presented CAN sure be confusing.

    Please Register or Log in to view the hidden image!



    Simply put, the magnetic north pole is in the Northern Hemisphere. The confusion usually arises because of the terms used when speaking of a compass. The "North Seeking" pole of the compass - actually it's own south pole - points toward magnetic north.

    Hope that helped.

    Please Register or Log in to view the hidden image!

     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. kingwinner Registered Senior Member

    Messages:
    796
    So the magnetic north and the north magnetic pole are both in the northern hemisphere now, right?

    The crazy thing to me is that some web sites say that the north magnetic pole is in the southern hemisphere and the word "geomagnetic north pole" is giving me a lot of confusion...
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. Light Registered Senior Member

    Messages:
    2,258
    Yes. They are the same thing.

    Yeah, the thing is that the terms "north" and "south" don't really mean anything in a physical sense in a magnet. The names were just used to match the directions humans had already established for getting around.

    Actually, the poles are set up by the way atoms in domains spin but the terms north and south are just arbitrary - just like when we started using the words left and right. It could have just as easily been the other way around. Nothing MAKES it have to be that way.

    Don't let that term geo magnetic bother you. It simply means the magnetism naturally generated by the Earth. ("Geo" = Earth just as in geo-graphy - graphing (mapping out or specific parts of) the Earth.
     
  8. Craven Moorehead Registered Senior Member

    Messages:
    31
    Well. Actually. Part of the confusion might be in the fact that geomagnetic north pole (the magnetic north pole of the planet Earth) is what would be considered the south pole of a magnet.

    In a magnet, the north pole is the pole where the magnetic force lines come out. But, on the earth, it's where they go in.


    Now I'm confused.
    What I said above is true and is likely some small part of the confusion concerning south poles, but apparently there is a difference between the magnetic north pole and the geomagnetic north pole aside from that...
    Weird.

    From wikipedia:

    "Magnetic North is one of several locations on the Earth's surface known as the "North Pole". Its definition, as the point where the geomagnetic field points vertically downwards, i.e. the dip is 90°, was proposed in 1600 by Sir William Gilbert, a courtier of Queen Elizabeth I, and is still used. It should not be confused with the less frequently used Geomagnetic North Pole. Magnetic North is the place to which all magnetic compasses point, although since the pole marked "N" on a bar magnet points north, and only opposite magnetic poles are attracted to each other, the Earth's magnetic north is actually a south magnetic pole."

    "The Geomagnetic North Pole is the pole of the Earth's geomagnetic field closest to true north. The first-order approximation of the Earth's magnetic field is that of a single magnetic dipole (like a bar magnet), tilted about 11° with respect to Earth's rotation axis and centered at the Earth's core. The residuals form the nondipole field. The Geomagnetic poles are the places where the axis of this dipole intersects the Earth's surface. Because the dipole approximation is far from a perfect fit to the Earth's magnetic field, the magnetic field is not quite vertical at the geomagnetic poles. The locations of true vertical field orientation are the magnetic poles, and these are about 30 degrees of longitude away from the geomagnetic poles."

    So. The magnetic north pole is where the field lines are vertical. But, I don't really understand what the geomagnetic north pole is. It says the field is not vertical there...

    I really have no clue what the geomagnetic north pole is then.


    Maybe the geomagnetic pole is where the field lines enter the crust. The magnetic north pole description would seen to indicate that that's what it is, but perhaps it's more of a virtual pole and maybe the field lines are only vertical beneath the crust?
     
    Last edited: Sep 18, 2005
  9. awaygood Registered Member

    Messages:
    1
    The cause of this misunderstanding is due to poor teaching which has led to a confusion between the names given to LOCATIONS ('Magnetic North' and 'Magnetic South'), and the POLARITIES of magnetic poles ('north' and 'south'). The key to correctly understanding this topic is to realise that the locations were named first, and the poles of a magnet were then named after those locations -NOT THE OTHER WAY AROUND!

    'Magnetic North' is a geographical location (which shifts, relative to True North) NOT a magnetic polarity. The end of a magnet which points to the location of Magnetic North was originally termed (for obvious reasons) its 'North-seeking pole' -eventually shortened simply to 'north pole' which then became the term used to describe the magnetic polarity of that end of the magnet. Since 'unlike poles attract', the magnetic polarity of Magnetic North (the location) must, therefore, be south. Hence, the earth behaves somewhat like a giant bar magnet whose south magnetic pole is located at the location of the earth's Magnetic North, and whose north magnetic pole is located at the earth's Magnetic South.

    So the fact that Magnetic North is a south magnetic pole is quite logical, and NOT the result of any confusion when they were originally named. Any statement to this effect is complete nonesense, and any teacher who suggests this simply doesn't know his or her subject well enough to be teaching it!
     
  10. D H Some other guy Valued Senior Member

    Messages:
    2,257
    It's a mathematical entity. If you know what spherical harmonics are it's easy to understand the meaning of the geomagnetic north pole versus the magnetic north pole.

    If you don't know what spherical harmonics are the discussions on the 'net are going to be a bit opaque. I'm going to talk about them obliquely, by way of analogy. I'm not going to do any mathematics. If you want to know the mathematics -- google is your friend. Search for "spherical harmonics" to get an idea of the underlying mathematics. Search for "International Geomagnetic Reference Field" (or IGRF for short) to get an idea of how spherical harmonics are used to describe the Earth's magnetic field.

    By way of analogy, think of the sound created by a musical instrument such as a trumpet, clarinet, or violin. None of these instruments emit a pure tone. A note played on a trumpet, clarinet, or violin instead comprises some fundamental frequency plus a rich set of overtones. Take away those overtones and you can't tell one instrument from another; all you have left is the sound emitted by a tuning fork.

    Spherical harmonics are in a sense a spatial analog of the Fourier series used to analyze sounds. The Earth's magnetic field comprises a dipole component plus a lot of other higher order spherical harmonic terms. Think of these higher order terms as the equivalent of overtones. Take away those higher order terms and all that is left is the dipole term. The geomagnetic north and south poles are defined in terms of this dipole term. Note that by definition the geomagnetic north and south poles are antipodal.

    Suppose you went to the geomagnetic north pole and tried to do some local experiments to prove that you are at the geomagnetic north pole. Can't be done. The geomagnetic poles are a mathematical construct. The spherical harmonics coefficients of the Earth's magnetic field are calculated by computing a mathematical best-fit of measurements of the magnetic field taken from all over the Earth to a finite spherical harmonics model. Those spherical harmonics coefficients are very useful for modeling the Earth's magnetic field. However, there is in a sense nothing to see/measure at the geomagnetic north pole -- move along, move along.

    The place to move along to is the north magnetic pole. There is something to see there: It is the point one the Earth's surface where Earth's magnetic field lines are oriented vertically and plunging into the Earth. The high order spherical harmonics (the overtones) do contribute to the magnetic field by quite a bit. The measurement at any one spot is the total contribution of all of the spherical harmonics terms.
     
  11. scifes In withdrawal. Valued Senior Member

    Messages:
    2,573
    different poles attract, so the north needle pole of a compass would be attracted to the south real earth pole and vice versa.

    that's what i understood of Light. am i correct?
     
  12. John Connellan Valued Senior Member

    Messages:
    3,636
    I believe magnetic north is somewhere in Canada currently isn't it?
     
  13. James R Just this guy, you know? Staff Member

    Messages:
    39,397
    This thread is 6 years old.
     
  14. John Connellan Valued Senior Member

    Messages:
    3,636
    Ha ha, just noticed that. Someody must have been doing a bit of rummaging through the archives yesterday.
     
  15. scifes In withdrawal. Valued Senior Member

    Messages:
    2,573
    wasn't me..and an old thread is as good as a fresh one..alas, old ones are even better, just look at the "science" discussed these days..idiots want to fly using magnets:facepalm:

    Please Register or Log in to view the hidden image!

     

Share This Page