I once read that there is such a thing as the earth's magnetic field. What is the earth's magnetic field? Is it a force in the direction of a compass needle? What angle does it make relative to some vertical line, looking down upon the earth?
The earth is a giant magnet, with a north and south pole. It's north pole attracts the south poles of other magnets and it's south pole attracts the north poles of other magnets. A compas is just a little magnet that, because of this, lets ou know which ways are north and south. The poles do drift a little and are not at the geographical north and south poles (i believe the north pole is somewhere in northern canada). As for what angle the magnetic fields make with the surface of the earth... it depends where you are. At the notrth and south poles they are straight up, halfway inbetween they are paralel to the surface. ============================================== 01-05-03, 11:00 AM Minnesota You read correctly Tsaeb, there is such a thing. It is thought to be generated by the constant circulation of the Earth's iron core. Within the earth, the Field is expressed by aligning itself along a straight pathway that emerges at the surface at two points: the North Geomagnetic Pole and the South Geomagnetic Pole (these two anchoring points do slowly change location with time). HOWEVER, the magnetic field itself does not emerge from these two points, but rather at two locations hundreds of miles away: the North Magnetic Pole and the South Magnetic Pole. These two poles wander even more vigorously than the geomagnetic poles. The magnetic field, emerging from the south point, flows up and over the Earth and then reenters the earth at the north point. However its journey is not smooth. Anomalies in the structure of the earth, solar emissions, and other factors disrupt the flow, not only bending it but creating pockets of lesser and greater intensities. Initially the field emerges from the Earth at a 90 degree angle, but immediately starts to bend, somewhat following the contour of the Earth in order to reenter the Earth at a 90 degree angle in the north. It is the location of its 90 degree exit and entry that define the two magnetic poles--nothing else. At present, the North Magnetic Pole sits in northern Canada on the Ellef Ringes Island about 11 degrees south of the North Geographic Pole. The North Geomagnetic Pole sits in the Kane Basin of Greenland, also about 11 degrees north oh the North Pole.
The needle of a magnetic compass aligns itself with this flow. If one held a compass vertically instead of its normal horizontal position one will detect the angle from vertical that the filed is flowing. At Houston Texas, for example, the angle is 60 degrees (I assume this will answer your question about how the field appears when looking down on it). Held horizontally, one can read the east-west direction of its flow. HOWEVER, with few exceptions, this direction will not point to the North Magnetic Pole. Various influences on the field twist it a bit, shifting its direction of flow either eastward or westward depending on location. Therefore, when reading a compass one must compensate for this deviation in order to obtain an accurate reading. At Denver Colorado, for example, the field is about 11 degrees off, whereas at Monte carlo there is no deviation. The crucial point to keep in mind is that a compass needle is not controlled so much by the positions of the Magnetic North Pole as it is by the configuration of the magnetic field immediately surrounding it.
01-05-03, 10:15 PM tsaeb methos5000: Thank you for the overview. You may want to help answer the questions which I have for Minn.
Minn.: Thank you for the in-depth analysis. Now, help! I understand the geographic north and south poles. My first question is what exactly are the geomagnetic north and south poles, because I do not understand their significance? I hope that I have a better understanding of the magnetic north and south poles. Generally, I understand that the magnetic field is the one each of whose points is relative to the earth. Yet, when I looked up the points of the geomagnetic and magnetic north poles, I found that they are far apart: approximately 33 degrees of longitude. My second question is what are the locations of the geomagnetic and magnetic south poles? With these locations, I should be able to determine whether the field is moving northwest, northward, or northeast. I suspect northwest. My third question is where can we find those specific deviational degrees relative to the earth of the magnetic field? Finally, my fourth question is can you better explain what one gets when one examines a compass at a particular earth location? I think that you were hinting at degree measurements relative to x axes and y ordinates, indicating that you may have been bearing in mind some right angles in a three-dimensional coordinate scheme.
01-06-03, 01:45 AM Minnesota Tsaeb
Locations of the poles:
As of 2001 the North Magnetic Pole is 80.0 north and 106.80 west. As of 2001 the North Geomagnetic Pole is 79.50 north and 71.70 west. For the two south poles (1998 data) the South Magnetic Pole is 64.70 south and 138.60 east. The South Geomagnetic Pole is 79.3 south and 108.50 east. The distance between the two north poles is 426 miles, and the distance between the two south poles is 1165 miles.
The geomagnetic poles
These are the two points at which the theoretical axis of the Earth's interior magnetic would break the surface. Think of a rod within the Earth whose ends lie at the surface. As I mentioned, this magnetic axis, is formed by the roiling molten iron core within the earth. And, because this axis is pretty straight the two geomagnetic poles are directly opposite each other.
A magnetic field does not exit and enter exactly at the ends of its poles, but rather exits and enters the Earth at differing angles, which depends on the distance from the nearest pole. This why the magnetic dip (the vertical direction) of the force field in Houston Texas is 60 0, whereas as one gets closer to the North Pole (geographic NP) the angle of entry increases. When the angle of entry becomes perpendicular to the surface, 900, it is called the Magnetic North Pole. Likewise, in the south, where called the angle of exit reaches 90 it is called the South Magnetic Pole. Now, why doesn't this happen at the Geomagnetic Poles instead of 426 and 1165 miles away? Well, unfortunately the reason is not fully understood, and from what I have read of it I would be incapable of summarizing what is known.
As I mentioned, the geomagnetic poles are much slower movers, often shifting no more than a degree or two each century.
You ask about specific deviations. Take a look at the map of North America at the following site: http://wapi.isu.edu/Field_Exercise/topomaps/mag_dec.htm The lines radiating outward from the north are lines of equal deviation: Deviation is the amount a compass will point away from True North (not necessarily from the MNP). That is, a compass placed on anywhere along any one line will give the same reading of deviation. They DO NOT indicate the flow of the magnetic field, as is often believed. So, line going through Los Angles indicates that a compass reading there will show a deviation (which must be corrected for) of 14 degrees, as will a reading taken in Billings Montana. But, a reading taken in Mobile Alabama shows that no correction is required (0 deviation), which is also true of Duluth Minnesota.
01-06-03, 09:23 AM methos Just to make it clear, the deviation is from 'true north' ... the rotational axis, not the magnetic north. All compasses will in fact point very close to the magnetic north pole unless you are close to power lines or other producers of magnetic fields. I don't think I gave you a very clear picture of why the magnetic fields are entering/exiting the earth at different angles at different lattitudes... hopefully this picture is a bit clearer than my words were... the dashed lines show the magnetic field. http://www.ngdc.noaa.gov/seg/potfld/img/faqpole.gif
01-06-03, 10:40 AM Minnesota I see that my link to the MNP wanderings does not work. Here is better site (scroll down a bit). http://anthro.palomar.edu/time/time_4.htm
If you will note on the map of magnetic declinations in the U.S. and Canada through the link I provided (previous post) you will see that a compass does deviate considerably from the north pole. At the northern tip of Main, for example, the deviation is 22o from True North. And because the MNP and the Geographic NP are reasonably close together this translates into a deviation to the MAGNETIC NP of 11o. Whereas this is not nearly the deviation to the NP, 11 degrees is still a significant deviation.
Also, in your link the illustration shows the GMNP incorrectly in alignment with the MNP (the angle of entry appears to be 90 degrees). I believe the problem is one of mislabeling, although because the latitude of the GMNP is 11.5 degrees from true north who knows what the illustrator was thinking. As I mentioned about the illustration in my link above, the author or illustrator also got it wrong. Unfortunately, such misrepresentations, both in illustrations and text are rampant among the various attempts, both in print and on the web, to explain geomagnetism. In fact, I don't know of any other phenomenon that is more poorly (even, badly) explained than geomagnetism, which, of course, goes a long way in explaining why people have such a hard time understanding it.
[This message was edited by Minnesota on 01-06-03 at 10:53 AM.]
01-07-03, 12:19 PM DvdGStwrt Yes and True North, truly isn't north because the Earth is slightly titled on it's axis - and it wobbles too~ Presently the north star is in the general direction of north, 50,000 years ago this was not so.
Other oddities about the Earths Magnetic Field is that it is not a homogenous field. In some places it is stronger than in others, and in some places the magnetic field lines bend and curve so your compass may register magnetic north a few degrees off.
The Magnetic Flux or Lines of Force are not constant, they move slightly and at different speeds.
The Further from the Surface of the Earth, the more movement they make. This is due to the pressure of the Solar Wind (The plasmas, particles and waves cast by the sun - waves such as photons (light) infrared (heat) UV) thus the Earths magnetic field doesn't form into a perfect sphere, instead it is warped and more egg shaped.
Magnetic Density is more on the sunward side of the planet than the Dark Side.
Did you know that the North Magnetic Pole and the South Magnetic Pole have switched before in the past? Well they have. Layers of rock with iron particles that were laid down in different ages have recorded faithfully the movement of the Magnetic poles.
It all connects to the interesting design of the physical Earth. For a planet Earth is the largest terrestrial planet in the Solar system. Terrestrial planets are those composed of metals, minerals (soils) rocks) This would include the Moons of the gas giants, Jupiter and Saturn - They are terrestrial in form, though not life sustaining.
Its closest sister is Venus in size and density. The density of the earth is not the same through and through. This is measured by the variations of the Gravitational pull. some areas which have a greater mass beneath the surface have a greater gravitational pull. Gravity is averaged out to be 32 ft per second (an acceleration force). It is theorized that the core of the planet is liquid nickel iron. Iron, or ferrous, is highly magnetic one can make a magnet out of iron. A better (stronger) magnet can be made out of nickel Iron.
Since the core is compressed by the tremendous weight of the rest of the planet, it is assumed that though liquid, the core acts more like a solid than a liquid. Relatively stable, moving very slowly (viscosity) however subject to the Earths rotation. The layers of the earth, starting out at the crust, or surface, and working downward do not rotate at exactly the same speed. Not only that, but we know that the Earth’s crust moves in different directions as well as in the direction of the planets spin. This is call Plate Tectonics and has been demonstrated by the relative positions of the plats. In California we have seen in a generation a movement of over a foot along the fault lines.
Beneath the Crust (The part of the Earth we see and live on) There is the Mantel a layer of liquid rock. This is what the crust floats on. It is theorized that the heat of the inner earth causes the mantel to have up drafts and down drafts. This may cause hot spots. The Hawaiian Islands are thought to be over on of these up drafts, the crust is thinner due to more heat. Thus there is a vertical (relative to the center of the earth) movement taking place while the mantel spins.
From these two well established ideas, we can hypothesize that the lower layers of the Earth also move in relation to one another and at different speeds.
An electrical generator produces electricity by the movement of a coil through a magnetic field. Electricity is part of magnetism, and a magnetic field is associated with electricity. Each wire you have in your home produces a tiny magnetic field.
Earth's composition is higher in this nickel iron than other terrestrial (Rock and metal) planets. Earth produces the strongest magnetic field of all the terrestrial planets and moons.
Good thing too, that magnetic field deflects the Solar Wind - giving us the Northern Lights protecting us from ionizing radiation and from plasmas. When the sun is more active (which it is every 7 years or so) the Display of the Northern Lights becomes brighter and extended further south.
If your trying to locate yourself on the planet, I would suggest a Solar Compass - it is the most accurate and was used (or thought to have been used ) by the Vikings. It is simply a disk with a post rising out of the center, and a wavy line drawn from one side to the other. The only other tool you would need is a clock - this way you can align the solar compass and then pick out true North compared to the date and time.
Or, you can just purchase a GPS transmitter ;-)
From CNN we have the following: March 20, 2002 (CNN) -- The North Magnetic Pole could soon abandon Canada, migrate north of Alaska and eventually wind up in Russia, according to a Canadian scientist. The magnetic pole, which has steadily drifted for decades, has picked up its pace in recent years and could exit Canadian territory as soon as 2004, said Larry Newitt of the Geological Survey of Canada. .....
This is just a Theorized Prediction There is no way to really say what the Magnetic Field will do next.
One theory states that the Magnetic Field’s harmonies ('Schumann Resonance') are changing, rising in fact. Scientists refute this, but the Resonance is known to fluxuate slightly. something to do with the Vibration of the Earth and the coming rise in the next step of human evolution (assumed spiritual) I came across that when looking for the Mayan account that foretells the Earths end on 12-21-2012. I assume that this has something to do with Earth Changes another fascinating idea which may bear some viewing but may again be another wistful thought.
David
01-07-03, 01:52 PM Minnesota
quote:Yes and True North, truly isn't north because the Earth is slightly titled on it's axis. . . .
This is highly misleading. In geology and astronomy "North" is a term reserved for one of the two terminal axial locations of a body. The quote implies there is greater North-South axis system to which a planet's rotational axis can be compared by using the ecliptical plane as a basis. Using the term "north" in celestial mechanics is almost always limited to the rotational axies of individual revolving bodies, not for their relationship to their orbital plane. So, in reference to Earth, "North" is specifically meant to indicate the axial pole of the planet that is uppermost when its orbit is seen to be going counterclockwise. That the axis is tilted to the plane of orbit does not mean that the North Pole of Earth does not coincide with its axial tilt.
01-07-03, 04:41 PM Minnesota My misstatement: "That the axis is tilted to the plane of orbit does not mean that the North Pole of Earth does not coincide with its axial tilt"
Should read:
"That the axis is tilted to the plane of orbit does not mean that True North does not coincide with our North Pole.
01-08-03, 01:39 AM tsaeb You fellows have given me a lot of work to do. I am busy with other projects right now, but I will get back to you when I again fail to figure out about what you are talking.
06-13-03, 02:21 PM DrGerard The following wording is valid only if you keep in mind that, when considered as a "giant magnet", the south pole of the Earth is near its geographical north pole and vice-versa...
quote:Originally posted by methos5000: The earth is a giant magnet, with a north and south pole. Its north pole attracts the south poles of other magnets and its south pole attracts the north poles of other magnets [...]
Historically, the "north pole" of small magnets and/or compass needles was defined as the part of the magnet/needle that "points to the north". This means that the Earth's so-called "magnetic north pole" is actually a "south pole" (it attracts the north poles of other magnets). We're stuck with a naming convention that was devised before the "big picture" was universally understood. This may be rather confusing whenever you want to consider the Earth as a magnet like any other, but that's the way it is...
06-13-03, 05:23 PM Minnesota The labeling of a magnet's northward pointing end as "north" came about because it pointed north and because it was more northward than its opposite end. It is improper to consider the Earth's magnetic south pole as sitting near the north pole. The Earth's magnetic poles are THEE determinant for any magnetic device they may interact with. So, it is a compass' south pole (the one we have decided to call its north end) that points northward.
06-13-03, 07:59 PM DrGerard The Earth's "Magnetic North Pole" is on the south side of its magnetic field. (Or is it?)
I love it! Minnesota clearly takes the opposite side of the issue. This will make the discussion less muddy for future readers... (When I commented on Methos5000's original prose, I had to concede that there were two ways to read it. My comment was about which of these two was correct.)
First, you have to realize that we're discussing history and nomenclature, not physics. Minnesota says that we may put an "N" on the poles of compass needles that point northward, although these are really south poles... I argue that the needles are correctly labeled but the Earth is not (the so-called "Magnetic North Pole" is the misleading name of something on the south side of the Earth magnetic field, near the geographic north pole).
The mislabeling of the Earth's poles is/was a "well-known" fact to me, which I remember seeing in print (although I have not [yet?] been able to find an authoritative reference for it). Therefore, either I was misled years ago or Minnesota is wrong... Which is it? How can one go about finding this out based on the rest of one's scientific "culture" without a trip to the library and/or many "properly labeled" magnets? (There has to be many of them, from independent sources, because a single magnet might be mislabeled, just as the Earth is!)
Well, a simple DC electrical circuit has also a "north" and "south" side based on the magnetic field it creates, according to a convention which is [hopefully!] consistent with the labeling of (small) magnets. A popular mnemonic is to consider the capital letters "N" and "S" and imagine them with outward arrows at their free extremities... These arrows would indicate the direction of the current if you place the proper letter (N or S) in the middle of the circuit (if "N" matches the direction of the current, you're watching the north side of the circuit). In other words, if you watch the south side of the circuit, the current circulates clockwise (this version is simpler to state, but tougher to remember). So much for the "cultural" side of the issue...
Now, I happen to to have a compass, a coil and a (current-regulated) DC power supply handy and I just ran an actual experiment to see if my two "ancient" pieces of knowledge were incompatible with each other or not. They're not: The south side of the coil does attract the side of the compass which normally points northward!
I could also argue that, at the time humanity decided on a way to label magnets, it was probably compelling to name/label the poles of magnets and compass needles alike... Anyway, I think the above experiment takes the cake, unless the suggestion presented in the next paragraph eventually reveals yet another contradiction...
If anyone reading this owns a commercially-labeled toy magnet [not a compass!] please, put it on a string to find which direction the side marked "N" points to and report the result in a post on this thread. The "N" should point northward, or else there is a contradiction between the conventions of electrical engineers and that of [some] toy-magnet manufacturers, and THAT would be worth reporting!
06-13-03, 11:29 PM DrGerard References about the labeling of magnetic poles:
This is what I found so far on the Internet to confirm the convention that "the North Pole of a magnet seeks the North Pole of the Earth" (meaning that the "North Pole of the Earth" is indeed a "south pole"):
I did find at least one web author who advocates Minnesota's viewpoint (unconvincingly). So far, no magnet manufacturers were found who do so... I didn't find anyone who mentions consistency with electrical engineering conventions (which is what I find most convincing, as explained in my previous post).
06-18-03, 10:00 PM Peteeo One must always remember not to purchase the Tate's brand name of compass.
For as everyone knows
"He who has a Tate's is lost". Wink
This message has been edited. Last edited by: DorianGreyed,
