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Discussion: Magnetic North Pole moving

in: Orienteering; General

Jan 15, 2019 5:40 PM # 
Every once in a while there are stories about this. Here's the latest.
Jan 15, 2019 5:50 PM # 
A few years ago, my 1960's base plate Boy Scout compass arrow flipped it's NS orientation. Was that an ominous early warning of what is to come? :)

Even just hiking, it is SO hard to remember that "White is North". [I'd just lost my thumb compass.]
Jan 16, 2019 5:12 AM # 
Reverse polarity has nothing to do with the location of the mag north pole.

It is easily fixed:
Jan 16, 2019 5:01 PM # 
Somebody take an old compass and try this out (reversing it intentionally) to see how easy it actually is. I have a reversed compass that I hang onto as a curiosity. As expected, it works poorly because it's now balanced for the wrong magnetic latitude. I'll also note that although this trick might work for older (or cheaper) compasses with metal needles, you're unlikely to have much luck with a modern racing compass that has a plastic needle with tiny rare-earth magnets near the pivot. (On the other hand, maybe these newer compasses are less likely to reversing in the first place.)

But yeah, the earth's field has really been moving quickly lately. It's a good thing that our maps are now in digital form, because we may need to start rotating some of them to correct the north lines.
Jan 16, 2019 7:18 PM # 
Monday's timely xkcd
Jan 16, 2019 7:26 PM # 
The only time I ever saw a reversed compass was when I was giving beginner instruction, and one of them was having trouble orienting her map. When I tried to demonstrate, the problem became apparent. It was a cheap department store compass and she told me it was new. But I don't understand the reversal mechanism, and I don't buy the cell phone in the pocket theory.
Jan 17, 2019 7:16 AM # 
Put your compass on top of your phone and watch the needle fluctuate wildly...
Jan 17, 2019 3:02 PM # 
The one I have that reversed was a Silva thumb compass (model 21? Top of the line back around 1990). No cell phones at the time, I used it at a meet, put it in the glove compartment of my car and drove home (about 2000 km). Next time I looked at it, it was backwards. I was a skeptic until I saw it happen. I have heard that if stored in a multi-compass case on their sides, unable to turn, some will be pointing the opposite direction from the others and will give in to peer pressure.

I don't buy the "backwards but 10 degrees off" assertion. Backwards is backwards, though it doesn't work right because the needle is unbalanced and one end drags on the bottom of the capsule.
Jan 17, 2019 3:58 PM # 
The same happed to me back in the '70ies driving from MA to Gatineau, Que. Also in the glove compartment. Could it be too close to the ignition coil? What a surprise when at the start line I was facing the opposite direction from everybody else. The race went OK keeping in mind that the needle was very unbalanced and sluggish.
Jan 21, 2019 10:56 PM # 
I encountered several compasses with reversed polarity when teaching an O program at a school several years ago. They kept all their Silva-style compasses in a plastic bag. Fortunately, I began the exercise by asking the kids to hold their compass properly and point in the direction of the red end of the needle. Four or five kids pointed south. I checked their compasses. They were indeed reversed. I brought them home and with a strong horseshoe magnet (used for turning pacemakers on and off), I stroked the bezel above each needle several times and the poles reversed. Problem solved. Now, I always have groups do this exercise before we begin an activity and I point out to people that they need to take precautions about where they store and place their compasses.

As for the MN pole moving, I just recently happened to look into this and was astounded to see how much it has moved in the past 30 years. I have an inflatable globe which I have fun with when I teach about MN vs. TN. I marked a circle around the MN pole where I found it referenced 30 years ago--near Victoria Island at about 100 degrees West longitude and 70 degrees North. This spot marked on my globe allowed me to show that if your are in northern Alaska, your compass needle points almost due east. Well, I have continued to use that line all these years and now realize that while I was standing still, the MN pole was moving. It was shocking to me to learn that the MN pole is now NW of Anchorage, soon to pass 180 degrees West longitude! Soon it will be near Russia. Needless to say, I have marked the 2001 and 2007 locations on my inflatable globe and will have to just let my students know that it is moving north and west at an increasing rate of speed. The article I read was (I think) at the Canadian Geological Survey which has better info than the USGS, in part because they are responsible for both predicting its location and doing field testing to determine its precise location every so many years.
One article I read did point out that while this movement may be an issue for instruments used near the poles, it will have negligible impact on compass use as far south as we are in the contiguous states. So I am not going to worry about it when I orienteer, but I will enjoy telling this story to future students.

This discussion thread is closed.