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Old 02-06-2019, 09:21 PM   #1
vtflyfish
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Map and Compass Navigation Issue

I saw this article in the NYT. Apparently, the magnetic North Pole is moving at a fairly rapid pace and is now only 25 miles from the actual pole. I assume this is enough of a change to render the declination angle on almost all maps useless. Should we be lining up with True North instead???

https://www.nytimes.com/2019/02/04/s...ole-model.html
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Old 02-07-2019, 12:44 AM   #2
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Not useless yet I don't think for distances very far from the pole (either one). The magnetic declination printed on the topo map of my location is 12degrees West. As measured on Caltopo, it is 12.9 W. The updated World Magnetic Model (linked from the NYT article) for the current date at my location indicates it is 12.8 W. An error of 0.8-0.9 degree is not really significant to navigation using the consumer grade orienteering compasses that most of us have.

There is an inconsistency in the NYT article. Regarding the location of the magnetic pole it states in one place of the article that "At the moment, it’s located four degrees south of the geographic North Pole". Four degrees of arc on the earth is approximately 280 miles (69 statute miles to the degree of arc). Later on it states: "If you were to use the current model to travel to the north magnetic pole, you would end up 25 miles away from where the pole actually resides." It can't be both. But hey, it is the NYT, not exactly known for the absolute truth.

You can actually measure declination yourself. Polaris is very close to the geographic pole, but not exactly. It is offset about 45' (3/4 of a degree) toward the big dipper, on a line between the big dipper and Cassiopeia. If observed at the time of upper or lower culmination (at its highest or lowest point on that line), then its azimuth direction is exactly true (geographic) north. Measure this direction with your magnetic compass and you will have the magnetic declination of your location. With care you should be able to be accurate to within about 2-3 degrees. It may be easiest to do this by aligning a couple of stakes in the ground, with tops sighted toward Polaris. Compare to the published declination on your map.

In any case, since I navigate mostly by terrain association anyway, 2-3 degrees of declination error on my compass is not going to get me lost. I'll wait for a more significant published difference before I make the adjustment.
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Last edited by Wldrns; 02-07-2019 at 01:06 PM..
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Old 02-07-2019, 08:57 AM   #3
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Quote:
Originally Posted by Wldrns View Post
Not useless yet I don't think for distances very far from the pole (either one). The magnetic declination printed on the topo map of my location is 12degrees West. As measured on Caltopo, it is 12.9 W. The updated World Magnetic Model (linked from the NYT article) for the current date at my location indicates it is 12.8 W. An error of 0.8-0.9 degree is not really significant to navigation using the consumer grade orienteering compasses that most of us have.

There is an inconsistency in the NYT article. Regarding the location of the magnetic pole it states in one place of the article that "At the moment, itís located four degrees south of the geographic North Pole". Four degrees of arc on the earth is approximately 280 miles (69 miles to the degree of arc). Later on it states: "If you were to use the current model to travel to the north magnetic pole, you would end up 25 miles away from where the pole actually resides." It can't be both. But hey, it is the NYT, not exactly known for the absolute truth.

You can actually measure declination yourself. Polaris is very close to the geographic pole, but not exactly. It is offset about 45' (3/4 of a degree) toward the big dipper, on a line between the big dipper and Cassiopeia. If observed at the time of upper or lower culmination (at its highest or lowest point on that line), then its azimuth direction is exactly true (geographic) north. Measure this direction with your magnetic compass and you will have the magnetic declination of your location. With care you should be able to be accurate to within about 2-3 degrees. It may be easiest to do this by alining a couple of stakes in the ground, with tops sighted toward Polaris. Compare to the published declination on your map.

In any case, since I navigate mostly by terrain association anyway, 2-3 degrees of declination error on my compass is not going to get me lost. I'll wait for a more significant published difference before I make the adjustment.
Thanks for that explanation, you're truly an asset.
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Old 02-07-2019, 09:09 AM   #4
JoeCedar
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Magnetic declination is, well, all over the place...
This link is a NOAA map with a slider to see the change over time.

https://maps.ngdc.noaa.gov/viewers/h...l_declination/
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Old 02-07-2019, 12:10 PM   #5
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Neat Link. Thanks, Joe.

(It's comical to watch the NYT act like they only just discovered this.)

Sure the pole and field change at varying rates. But the changes don't happen fast enough that you cannot compensate for them if you are paying attention, as Wldrns pointed out.

The bigger changes that disrupt people's navigation performance are changes in location. People travel, and then forget to reset the declination on their compasses, which can now be VERY far off. Go to Yosemite, and the declination will be 28 degrees different from here in the Adirondacks. That's enough to disrupt your navigation, for sure.
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