
Compasses to point true north for first time in 360 years in UK - sohkamyung
https://www.theguardian.com/science/2019/aug/30/compasses-to-point-true-north-for-first-time-in-360-years
======
shartshooter
The concept of a compass not pointing to True North was something I struggled
with at first when learning orienteering because I had assumed north meant
north. The reality is that you have a Grid North, Magnetic North and True
North.

That said, orienteering is one of the most valuable skills I think a person
can learn but it can be hard to grasp learning solo. For those not familiar
there are really two ways to go about it: \- Dead Reckoning \- Terrain
Association

Dead Reckoning is all about planning waypoints and using your compass and pace
count to get you there. For example: I need to walk 5km at 220° then 2km at
90°, etc.

On top of that, it's easy to make simple mistakes when planning your route.
Errors when converting from grid to magnetic(and visa versa) can put you off
by a few grid squares so it's important to understand terrain association
which is a technique of studying the terrain on a map, plan a route and use
those visual terrain features to guide you(If the river is supposed to be on
your left but it's on your right, something is wrong).

Having both techniques in your back pocket are essential, but like any skill,
they're perishable so you have to practice often.

Some key mistakes people tend to make when orienteering: \- When you're dead
reckoning through the forest, make sure you switch which side you favor. For
example, if your compass points directly at a tree do you step to the right of
it to go around or to the left? Most people will pick their dominant side and
tend to veer to the right over time. This won't be corrected by staying on a
specific azimuth. \- Night time is challenging when orienteering in a forest
with no roads/creeks/etc to handrail. You often can't see more than 10-20
meters and there's no terrain for you to associate with. \- After you plan
your waypoints out, do it again from scratch. You likely made a mistake. The
protractor you used to get your heading represents your grid angle, every map
will have a GM Adjustment(grid to magnetic) you'll need to make.

Source: I'm a former US special ops soldier with hundreds of hours using a map
and compass humping through the woods.

~~~
Jonnax
I didn't know about having to correct for magnetic vs grid north.

Are the maps specialised for orienteering? Since I've never seen that info on
a standard street paper map.

Is it something that a digital compass could automatically do? Especially
since the article is indicating that magnetic north drifts.

~~~
isostatic
In the UK the three compass points are on OS maps, sometimes with the changes
predicted for multiple years.

The older the map the less useful it is. You then have metal in the local
rocks which can cause problems.

Terrain recognition is far easier, there is far more error correction built
in, but if you are hit by a patch of fog and visibility is down in to 30m (let
alone 3m!) you need dead reckoning.

Trouble is even a 1 degree error can turn into significant errors after a very
short distance.

------
kylek
Here's a nifty visualization of magnetic pole location and strength from NOAA-

[https://maps.ngdc.noaa.gov/viewers/historical_declination/](https://maps.ngdc.noaa.gov/viewers/historical_declination/)

edit: Some more on this stuff here (probably to be taken with a grain of salt,
but neat no less)-

[https://magneticreversal.org/](https://magneticreversal.org/)

~~~
cwmma
I'm usually a Mercator apologist, but this is a really bad map to use that
projection for

~~~
jessaustin
In this case they want to preserve directions rather than e.g. area or
distance, so Mercator is suitable. (You can click the tabs on the right side
to see polar projections.)

------
chrystianv
I have been working on a smartphone AR visualizer for the magnetic field. I
was awarded a grant from the National Science Foundation to develop this app.
One of the surprising things I found was the inclination of the magnetic field
vector. You can test the free Android app here:

[https://www.vieyrasoftware.net/physics-toolbox-
ar](https://www.vieyrasoftware.net/physics-toolbox-ar)

------
tialaramex
So far as I understand it the existence of a magnetic "North Pole" is a weird
temporary coincidence, like if you discovered a friend's phone number is the
same as yours but in the opposite order of digits. It doesn't mean anything
and it might change also for no particular reason, so you should probably
avoid depending on it if possible.

Magnets are more or less bound to point somewhere on a planet containing a
core of molten iron, but my understanding is that it could easily have been
towards Australia, or Mexico or anywhere.

~~~
BurningFrog
No, it's almost always roughly aligned with the axis of Earth's rotation. I
believe that's because it's related to the rotation of the internal molten
iron core.

Though every few million years, the north and south magnetic poles swap, for
unclear reasons.

~~~
double0jimb0
We are also about 350,000 years overdue for a magnetic pole swap. [1]

Also, it cycles at 300,000-400,000 years not millions.

[1] [https://futurism.com/earths-magnetic-poles-overdue-
switch](https://futurism.com/earths-magnetic-poles-overdue-switch)

~~~
24gttghh
Looking at a map someone else linked to, the pole has shifted drastically in
the last 50 years. Could that be an indication that it is in the process of
shifting? It's been moving North in a straight line for the past 100 years,
and now it's actually heading South towards Siberia.

[https://maps.ngdc.noaa.gov/viewers/historical_declination/](https://maps.ngdc.noaa.gov/viewers/historical_declination/)

~~~
BurningFrog
> _Could that be an indication that it is in the process of shifting?_

It _could_ be. Since we've never seen a shift, we don't really know how it
looks.

And a shift takes a few thousand years, so we can probably be centuries into
it before it's clear what's happening.

~~~
jobigoud
Ah, too bad, it would have been great drama if it flipped instantly! Or even
better, oscillated a few times over the course of a few years before settling
in.

~~~
BurningFrog
I mean, for all we know it _might_ oscillate like that.

I doubt the geological record is fine grained enough to tell fast oscillations
apart from a slow drift.

