Ask Hackaday: Earth’s Magnetic Field Shifting Rapidly, But Who Will Notice?

Just when you though it was safe to venture out, the National Oceanic and Atmospheric Administration released an unexpected update. Magnetic North is on the move — faster than expected. That’s right, we know magnetic north moves around, but now it’s happened at a surprising rate. Instead of waiting for the normal five year interval before an update on its position, NOAA have given us a fresh one a bit earlier.

There are some things that we can safely consider immutable, reliable, they’ll always be the same. You might think that direction would be one of them. North, south, east, and west, the points of the compass. But while the True North of the Earth’s rotation has remained unchanged, the same can not be said of our customary method of measuring direction.

Earth’s magnetic field is generated by a 2,000 km thick outer core of liquid iron and nickel that surrounds the planet’s solid inner core. The axis of the earth’s internal magnet shifts around the rotational axis at the whim of the currents within that liquid interior, and with it changes the readings returned by magnetic compasses worldwide.

The question that emerged at Hackaday as we digested news of the early update was this: as navigation moves inexorably towards the use of GPS and other systems that do not depend upon the Earth’s magnetic field, where is this still relevant beyond the realm of science?

Finding Your Way with Map and Compass

This is how the British Ordnance Survey publish the magnetic offset in the margin of their printed maps. [Fair use]
This is how the British Ordnance Survey publish the magnetic offset in the margin of their printed maps. [Fair use]
Every former Scout will have learned how to take a compass bearing and relate it to a map. But do you remember learning the difference between the compass needle and the grid on that map?

Generally map publishers use two standards, True North is used for the map grid — it’s where longitudinal lines meet at the northern tip of the planet. Magnetic north is where your compass actually points and has to do with that pesky moving target. Publishers will note the local offset between Magnetic North and the North of the map grid. Anyone trying to earn their Map Reader badge will add or subtract from their compass reading as required. In more serious fields where precise navigation is critical, every ship and aircraft will have a magnetic compass as an aid to its navigator.

Where Does the Compass Rest in Our Modern World?

It’s true then, that a magnetic compass is a useful instrument, and given one along with a good map or chart everyone from a pimply teen in the wilderness to a veteran sea-dog on the bridge can use it to make their way across the land or the ocean. But the modern Scout has a smartphone with GPS in their pocket and both pilots and captains have had reliable (in level flight at least!) gyrocompasses for decades before they ever saw a GPS. Is there still a place for a magnetic compass, or will it eventually go the way of the astrolabe or the Decca Navigator?

The most obvious place we still see a magnetic compass is automobiles. They’re digital now, but still rely on the earth’s magnetic north pole. Your smartphone has one of these sensors as well and it’s used in conjunction with inertial sensors and GPS readings when using your phone for navigation. But we’re really looking for more places where our lives are affected by magnetic north, so do tell in the comments below!

In the event that everything in our high-tech house of cards has failed, and all that is left is the magnetic compass, this instrument could prove life-saving. With this convenient excuse of a magnetic north heading update, now is a great time to discuss all the ways this simple phenomenon has had profound impacts on our lives and the development society.

92 thoughts on “Ask Hackaday: Earth’s Magnetic Field Shifting Rapidly, But Who Will Notice?

  1. Magnetic compass is required equipment for aircraft flight. The gyro compasses will drift and must be corrected (sometimes as often as every 15 minutes). During my long-distance solo flight for my private pilot license, the vacuum pump failed and therefore the gyro compass. I finished the final 2 airport landings with only magnetic compass.

    1. Is it possible that a microscopic Black Hole accidentally created by Cern, has got loose inside the Earths’ internal Gyro Magna? Thus creating an increased semi-spiralling magnetic hotspot? ; – )

      1. Seems like if you’d have done your job, we wouldn’t have to wait for a man to say it before you’d be willing to accept it. “Red herring”? Wouldn’t that mean she was being intentionally deceitful, to steer someone away from the truth? I don’t think you’re using that correctly.

    1. Well, Decca Records had a lot of great tech, in a parallel universe you could easily end up with a Moody Blues album called Magnetic Field Shifting Rapidly.

      Actually it could be an alternate title for their song Tortoise and the Hare.

      1. A much better explanation of Decca Navigator is as an autonomous land based navigation aid using multiple stations. And yes, it sprang out of the same roots as The Decca Record Co.

  2. “Is there still a place for a magnetic compass, or will it eventually go the way of the astrolabe or the Decca Navigator?”

    You’re mixing two things. An astrolabe is a device for measuring position by the location of stars, and that *method* is still used quite a lot, with star trackers. It’s by far the best way to orient something if you want arcsecond precision – you’re not getting that with GPS.

    Likewise, saying that a simple magnetic compass isn’t that useful anymore for navigation finding is *not* the same thing as saying that direction-finding against the Earth’s magnetic field isn’t useful. Having to update the Earth’s magnetic field infrequently isn’t exactly a big deal.

      1. It’s a sun sensor, which is obviously the same idea, but far more limited (it only gives attitude). Since Earth is inside Mars’s orbit, it’s always within a fixed distance to the Sun so that’ll get you very rough pointing. But I think it’s clock fault behavior (that is, it wakes up and has no idea when or where it is) relies entirely on the low-gain (non-pointed) antenna.

        Star trackers are extremely common on almost any astronomical mission, though, and not even space-based: balloon-based ones use star trackers because GPS doesn’t come close to how accurate a star tracker is.

        1. Star trackers are also used on lot’s of military systems. Missiles (ICBMs), aircraft, smart weapons (cruise missiles) all still use star trackers. You can’t count on GPS when things go bad.

  3. In deference to the two or three Hackaday readers who live south of the Equator, there is actually a South Magnetic Pole. Compasses in the Southern Hemisphere point to that pole, not the one that Santa Claus uses for navigation. While the North Magnetic Pole is galloping along at a frenetic pace, its southern partner has chosen to relatively stay put. But in this day of reliable worldwide GPS, runways, airways, ocean courses, etc should get with the program and switch to a True heading model for everything. Sure, a magnetic compass can be used in an emergency; just have an ideal of the local correction and you won’t get too far lost. Steve

    1. Whoa, whoa, whoa… slow down a second there. We use “magnetic north”, but compasses don’t have to choose between pointing to magnetic north or pointing to magnetic south. They do both at the same time. What’s actually happening is that compass needle’s south pole and north pole align with the magnetic fields of the earth’s north pole and south pole at the same time. So no matter where you are on the earth you can use the same compass, but you must have magnetic offset information for the area you are in to reliably use a map.

      1. I agree with the earth acts as one big magnet but a compass designed for use in one hemisphere might not work well in the other. This is due to the magnetic field having both horizontal and vertical components -more vertical the closer you get to the poles. Compass manufacturers balance compasses for use in 1 of 5 zones, with some overlap. Suunto has a patent for a “global needle”

        1. As long as you’re in temperate or tropicsl lattitudes any compass will work well enough to get you around. Suunto & other companies make precision compasses for surveying, so balancing them for vertical pull is important. Local declination is probably larger than vertically induced error for most regions.
          If you’re using the compass with an IMU or other instrument only nav that error becomes important, but for human guided navigation it’s negligible.
          Also provided you’re not around large ferromagnetic ore bodies.

        2. “a compass designed for use in one hemisphere ”

          Huh? I thought you were talking rubbish, but a bit of Googling confirmed! The needle is weighted at one end to compensate for the fact that it wants to point up or down as well. Thank you – You taught me something

    2. Haha nice one. The value of pi is different here too. I had to adjust the notches on my slide rule along with my compass.

      More seriously, I actually brought my compass with me when I moved south of the Equator. I worked as a biologist before GPS was practical, and some habits die hard. It still points towards the North Pole, as does the software on my smartphone.

      I think our technology can more or less tolerate magnetic pole drift — but our Feng Shui is going to be just awful.

    3. Im sorry what planet are you from? A compass works by way of magnetic attraction. By what you are saying here is that when you cross the equator all copasses chage magnetic orientation and point south. Gosh if thats the case then the earth is truely flat, and it is only our warped sence of perception that makes it appeare round

  4. I wonder if animals that may rely on a sense of direction, through the earth’s magnetic field, for migration will be able to use other inputs to adapt to the increased rate of change. Nature’s kalman filter perhaps.

    1. I would think of it like how we perceive sound. You hear a persistent sound and you can zero in on which direction it is coming from. But if that direction is slightly off, you’ll still eventually get there.

      I have nothing to base this on other than my own intuition. (and of course Wikipedia

      On the other hand, magnetic poles do flip through extremely long periods of the earth’s history. If south became north that would be a problem for these animals — except that this happens quickly only if looked at on geologic timescales; it takes a few thousand years.

      1. If south became north that would be an episode of South Park, which would really be North Park then?

        The true South also thinks any North designations should be removed from roads etc. For example I75 runs South and Souther.

        It is all very complicated. Just don’t think about it. It’s in good hands.

        The more amateur scientist question is can you see the pole move. I am thinking a simple magnetic compress located as away from anything as you can locate it, with a small first surface mirror mounted on it, and a laser aimed at the mirror and the from the laser read out on a scale a long distance away so a very small displacement in the compress would result in a much larger deviation of the spot. The compass would need to be shielded from wind and seismic activity. It sounds inexpensive enough to try and it may be interesting.

        1. This sounds like a great science project.

          But also the most boring webcam feed in the whole world. Watching paint dry too exciting? Try watching the poles move!

          Seriously, though. If you’re far enough north, it could totally work. Timelapse?

          What did the snail say when he climbed on the turtle’s back?


          1. I was thinking more like a pencil mark than time lapse, though if you could get an old smartphone out there with a time lapse app. You already need power for the laser diode, but I think that would be modest and you only need to power that up when you take a reading. The laser would need to be far enough away for the magnetic field from it’s power to not be sensed.

        2. To see how fast the SouthPole moves each year search Google with: South Pole Marker …A new stake is hammered into the snow-ice each January 1 by the scientists-engineers-workmen that live there.

      2. Mike, with that comment you have hit on an instrument that uses magnetic north. Magnetometers. They measure the direction of the magnetic field in rock and need to know local magnetic north in order to help cancel out the offset. Now they may determine magnetic north by having another magnetometer at the other end of a stick (one on the bottom, one on the top), but, of course, even the magnetometer at the top of the stick is impacted by the local geomagnetic field. There are some cool maps made using high altitude magnetometers. The field isn’t as uniform as you might think. Local variations of ferrous material in crustal plates distorts the field.


  5. One way to improve the accuracy of a magnetic compass reading is to align a “compensating compass”. This is a compass that has a pair of small magnets mounted in threaded alignment holes. For example, if you are going to align one in an automobile, you use a topographic map to find a pair of roads that are true North-South and true East-West. Carefully parking parallel to the curb on the North-South road, you use a screwdriver to adjust the North-South magnet so that the compass needle points North. Then you do the same with the East-West magnet and road. Since this second adjustment affects the first, you must repeat this procedure three or four times for the best accuracy. As pointed out in the article, the Earth’s magnetic field changes from time-to-time, so whenever this happens to a sufficient degree, the above procedure must be redone. Whenever it is realigned, you will get readings that are very close to true. Until the Earth changes again.

    1. I’m pretty sure that’s incorrect. The point of compass compensation magnets is to null out any magnetic influences in the vehicle/vessel/aircraft, so that your compass more likely to give you accurate MAGNETIC readings.

      (on a boat, the process of nulling any anomalies, or at least making note of them, is called swinging a compass)

      Practically-speaking, it’s still very practical and easy to use a compass to keep a heading on a boat: get your course from an electronic or paper chart, convert to magnetic, then steer to that compass heading. Driving/sailing with your nose pressed to a GPS/tablet/phone, or being a slave to that “In 100 meters, turn LEFT” is for wussies.

    1. I believe you have confused Deviation (compass error caused by magnetic disturbance aboard the vessel) with Variation, the difference correction to be taken in account between Magnetic North and the North Pole at the point where the vessel is located.

      Deviation is constant as long as the compass stays in the same place aboard the boat, with respect to any magnetic disturbing factor (like an engine).

      Variation changes with the changing position of the vessel with respect to the Agonic line, which is an imaginary line around the earth passing through both the north pole and the north magnetic pole, on which is the only place when an uncorrected compass needle points to true north.

  6. Magnetic ants and migratory birds come to mind but I am assuming (since this has been happening long before humans invented compasses with which to notice this) that they have their own evolved calibration and compensation mechanisms already.

  7. There is a definite use for compassed even if you are willing to trust navigation entirely to GPS. And that is direction finding. Sure a GPS can say WHERE you are, but if you should then “go east” without a compass of some form you still won’t know the direction from you to your destination. You can’t you use multiple GPS receivers and find relative positions as you typically don’t get GPS resolutions on the m or cm scales needed for this kind of thing. And in plenty of circumstances, it is not appropriate to try travelling in a direction for a little while and see how your GPS reading changes so as to work out which direction to go in. You need orientation information. This is especially important if you are, perhaps, trying to aim a high gain communication system to a receiver. Also if you are an autonomous ship passing through a canal it helps to know which way your bow is pointed. Just because you can have non-compass mean to know position doesn’t mean you don’t need orientation.

    1. This happened to me one time mushroom foraging; I knew I was going in (very small) circles, both because GPS said so, and because “hey, didn’t I just pass this tree?” But even with my topo map, it was hard to figure out which of two (barely visible) peaks was the correct one to navigate by. Until I got out a compass, anyways; then it was easy to understand my wrong turns.

      Without the compass it would have been as you said; I’d have had to travel hundreds of yards to be sure. And hopefully somehow in a straight line.

  8. While we use GPS for position, we still use compasses for orientation, even in fancy toys like phones. So it does matter to daily life… although it might take a while for a 9 arc minute annual drift to add up to something that matters when you’re trying to figure out directions.

    And the people in the southern hemisphere have enough weird stuff to worry about without the pole shifting. The SAA alone is weird enough! (Although the close alignment of the magnetic dipole to the Earth’s rotation is actually a weird thing. The dipoles and rotation aren’t at all aligned or centered in the Jovian planets.)

  9. ” In more serious fields where precise navigation is critical, every ship and aircraft will have a magnetic compass as an aid to its navigator.”

    This sentence makes no sense.

    1. No, just a better compass. A good compass has a n adjustment for this, because the deviation is not the same everywhere. In fact, the offset is what is written on the map. You adjust your compass to match the map +/- deviation change since the map was published.

      I have a few maps that are out by >5º. Or were 15-20 years ago. More now. :)

      1. Yup. One of my compasses is an inexpensive orienteering model which allows you to offset the needle alignment marks from compass 0, so that if you offset by the area’s known variance, the compass dial will give you true bearing.

  10. All you have to do is remember two Mnemonics: T-V-M-D-C and D-A-W
    For TVMDC, it’s True Virgins Make Dull Company – and for DAW, it’s Down Add West and the first one for conversion is:
    True………… Heading to the North Pole: True North on the nautical chart;
    Variation….. Difference correction required depending on your distance from Agonic line;
    Magnetic…. You compass’ Magnetic North, corrected for Variation;
    Deviation….. Correction required for onboard magnetic disturbance from metallic objects;
    Compass….. Your compass’ corrected Compass heading with Variation and Deviation taken into consideration.

    All you have to remember is when going Down the classifications, you must Add West degrees, when correcting your compass’ Magnetic heading to the True North, you must Subtract degrees.

    GeneGrossman at

  11. If one still uses azimuth/elevation for pointing a satellite dish, etc., this variation in the location of magnetic north in relation to the “fixed locations” of geosynchronous satellites in the sky, most especially if the two poles completely swap, could cause some disparity in how accurately your dish is pointed.

  12. “The most obvious place we still see a magnetic compass is automobiles. They’re digital now, but still rely on the earth’s magnetic north pole.”

    But who actually uses the compass in their vehicle for navigation anymore? My 02 Silverado has one built into the rearview mirror but I never use it for anything.

    1. I find a compass useful to, for example, make sure I joined the right lane of the motorway to go in the direction I want.

      I once managed to navigate between two point 150 miles apart on the basis that I would either hit the sea or a river if I headed SE and my destination was just south of the main bridge (the Humber Bridge).

      Though I didn’t use a compass that day, I used the fact that it was the early noughties, people still had satellite TV, and satellite dishes point South (in the UK)

    2. Use mine regularly. Had to teach my fiance how to navigate with a compass. When you know a place your going is roughly 30 miles north and 5 miles west from your current location. You don’t really need a map, just keep track of how many miles in each direction you have traveled.

  13. The compass (and a map) will probably be my primary instrument for a long time when hiking or in nature. A GPS require batteries, and have a screen thats bright even when at lowest illumination at night. Yes I use a hiking GPS to get fix points and keep track of average speed, but the compass is my main tool to hold a direction when the sky is overcast, in a forrest or with low clounds and fog. Hell I have used it in the foreign cities where I have a hard time finding or reading street signs. A Suunto watchband compass and a Silva compass is always on me when hiking.

    I know of several people thats gotten lost because they had only GPS and not a lot of orienteering common sense. And the GPS failed. Batteries run out, or screen cracked from dropping it and so on. The phone is a really good “do a lot” backup (GPS, compass, camera, musicplayer, info storage), but without navigation apps with maps that work OFFLINE theyre not to be trusted in a lot of locations.

    1. That’s true, high frequency signals don’t penetrate rock sufficiently. The very very low frequency signal of the earths magnetic field does. But it can be distorted by iron deposits.

  14. Magnetometers are more important than ever before. This article is very misinformed.

    There is literally no other way to determine bearing in a robotic platform other than with a compass.

    GPS just says you are here, not which way am I facing. Drones, aircraft, ships, cars all rely on magnetometers constantly for their ability to navigate.

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