Magnetic North Vs. True North

[Jeanway 0]

Can you explain this phenomenon nik?

[nik 0]

Why magnetic north is not geographic north? More appropriately, why is goegraphic north not magnetic north. There's two simple answers, and I leave you with a question. The first answer is: It probably never was. When the Viking first started using lodestones to find their way in the fog, and rennaissance thinkers began to think about maps, there may have been some discrapancy in the determination of "north" based on astronomical observations, and the way

the compass needle pointed.

The second answer is that the geomagnetic north pole drifts. It moves measurably over the span of a year. Pretty cool, huh?

 

Why does it drift?

[Jeanway 0]

Either has something to do with,hmm, gravitational pull or changes caused because of tectonic activities? I never thought about that. That's why a ship's compass needs adjusting regularly. I know an auto-gyro spins so it would have to go with gravity?

[headborg 1]

i believe the answer to the drift question lies in the fact that the earth's core is a large iron ball surrounded by a sea of molten iron/metal/ore..magma creates a large electro/magnetic field which sometimes the core drifts alittle. something like that.

[Jeanway 0]

So it is tectonic changes then. How do you know all this?

[nik 0]

i believe the answer to the drift question lies in the fact that the earth's core is a large iron ball surrounded by a sea of molten iron/metal/ore..magma creates a large electro/magnetic field which sometimes the core drifts alittle. something like that.

Pretty much. I'm no geophysicist, but the crust essentially "floats" on the earths core, and so they can indeed move w.r.t. each other. The core has a lot of ferromagnetic material in it, and so you can see how this might happen. When we add components of

angular momentum, as well as things like the "Hall effect", we can get "nutations" in the

magnetic poles, which have been postulated to sometimes result in complete

pole reversals.

 

OK, talking about my work again. Neutron stars have pretty robust magnetic fields

(well.... freakishly phenomenal magnetic fields.) However, they are also thought to be superconducting. What that means is that magnetic "flux tubes" within the star can

"pin" - get stuck so to speak - so that they affect the motion of the star. We see

neutron star pulsars which actuall will "spin up" and then "spin down" and then have

"crust quakes" becuase this flux tube pinning is creating instabililties. Neat stuff.

[Odie 0]

I will try to answer question as best as a Quartermaster in US Navy. My primary job in the Navy is navigation.

 

Magnetic north is the north direction shown on a compass determined by the earth's internal magnetic field. It is constant state of change. Currently Magnetic north is about 77 degrees north latitude, 102.3 degrees west longitude, which is off the tip of Lougheed Island in northernmost Canada.

 

True north (Geographic north)(90°N, where all meridians of longitude intersect) is the location of the earth's axis of rotation and is the basis for lines of latitude and longitude. 0°N, meridian is Greenwich, England.

[Jeanway 0]

Thanks Odie, that was the best explanation I've ever heard { seen }. All I knew was that we always had to be adjusting the compass all the time. One degree off and we were sunk :) Not really, just a few miles off. You know what I mean. Ever hear of Mid-night Drift?

Edited April 21, 2004 by Jeanway

[Odie 0]

Thanks Odie, that was the best explanation I've ever heard { seen }. All I knew was that we always had to be adjusting the compass all the time.  One degree off and we were sunk :P Not really, just a few miles off. You know what I mean.  Ever hear of Mid-night Drift?

I am glad I was helpful. Lately on stf.net I keep on running into several questions that involves my job. <_< No, I have not heard of Mid-night Drift. Have you? I will tell you something about the magnetic field that gives me a scare.

 

Click for Spoiler:

The magnetic poles are about to reverse themselves anytime now. It is in fact overdue for a reversal. I really don't know how this will effect us, but it will be interesting. The Observer | International This link has more information than I can give you. This maybe one of reasons for our climate problems. Edited April 22, 2004 by Odie

[Jim Phaserman 0]

Odie, me and you should work together. you do the navigating and driving, and I'll blow things up.

[Odie 0]

EJP, just name the ship and the place the you want to destroy. I will get you there!

Edited April 22, 2004 by Odie

[WEAREBORG4102 0]

It is true that the magnetic poles will flip as they have not flipped in approximately 300,000 years...

Oh and the plates are convected on the asthenosphere on the lithosphere on the mantle on the core...

Oh and geothermal heat is not the magma...

It's actually radiational decay from the isotopes that created the universe for those of you who believe the big bang theory...

[Jeanway 0]

Thanks Odie, that was the best explanation I've ever heard { seen }. All I knew was that we always had to be adjusting the compass all the time.  One degree off and we were sunk Not really, just a few miles off. You know what I mean.  Ever hear of Mid-night Drift?

I am glad I was helpful. Lately on stf.net I keep on running into several questions that involves my job. No, I have not heard of Mid-night Drift. Have you? I will tell you something about the magnetic field that gives me a scare.

 

 

<h4 style="cursor:hand" onClick="expandit(this)">Click for Spoiler:</h4>

<span style="display:none" style=&{head};>The magnetic poles are about to reverse themselves anytime now. It is in fact overdue for a reversal. I really don't know how this will effect us, but it will be interesting. The Observer | International This link has more information than I can give you. This maybe one of reasons for our climate problems.</span>

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so Odie, what's is your theory about this? Do you have one?? Oh the Spoiler didnt work for me, I read this in reply.

[fenriz275 0]

Let me see if I understand this correctly. The poles are caused by the spinning of the Earth's core. Their location on the Earth's surface 'drifts' because the surface of the Earth floats on a liquid center. Ok this makes sense to me but why do the poles flip? What causes that?

 

I have another question that just occured to me. Does the Moon's gravity affect the movement of the Earth's core? I know it affects the tides so I was wondering.