<p>Consider, instead of looking at an Earth map of Magnetic Declination, looking at a map of the Earth's magnetic field:</p>
<p><a href="https://i.sstatic.net/37I1k.gif" rel="nofollow noreferrer"><img src="https://i.sstatic.net/37I1k.gif" alt="enter image description here" /></a></p>
<p>Now trace a line across North America in such a way as to intersect the magnetic lines at locations where they are perpendicular to true north.  You should end up tracing out the green line in the image posted in the question.</p>
<p>Read on if that sounded confusing: Instead, find and circle the points on the lines in the map of the Earth's magnetic field where the curve of the line is perpendicular to an imaginary line drawn from the true North Poll to that point. When done, the points should all be on the green lines in the map in the posted question above.</p>

CC BY-SA 4.0
2023-06-24T14:13:51.347Z
2023-06-24T14:13:51.347Z
st2000
<p>A pole is a point. If you have two points then there are places where they line up if you'd look towards them.</p>
<p>For the geographic and magnetic poles we use &quot;declination&quot; to describe the angle between the direction towards geographic north versus the angle that the magnetic compass needle points to.</p>
<p>If you are in a place where both line up, then the declination is 0°.</p>
<p>Plotted on map those places form crooked lines because there is <a href="https://en.wikipedia.org/wiki/Earth%27s_magnetic_field#Geographical_variation" rel="nofollow noreferrer">geographic variation in Earth's magnetic field</a>.</p>

CC BY-SA 4.0
2023-05-30T17:12:06.017Z
Please read the question carefully before attempting to answer. I made it now clearer with my edit.
new editor
CC BY-SA 4.0
2023-05-31T06:37:45.447Z
What is wrong with my answer?
bugmenot123
CC BY-SA 4.0
2023-05-31T14:52:39.437Z
You explained that "there are places where they line up if you'd look towards them". I know that. And that should be only in two lines of longitude - approx. 0 and 180. But on the map there are many different locations **where** they don't line up which also have zero declination. And that's my question.
new editor
CC BY-SA 4.0
2023-05-31T19:30:58.050Z
They line up in those places because of variation in the magnetic field as I said. Lining up means the direction of the "magnetic needle" and geographic north here, not against the *geographic* location of the magnetic pole.
bugmenot123
CC BY-SA 4.0
2023-06-07T13:46:43.517Z
@bugmenot123 is spot on here - the magnetic field varies geographically and the magnetic dip poles are not symmetrically opposite each other across the globe. 

Declination is the angle between geographic north and the local direction of the magnetic field, which is the direction in which the horizonal part of the magnetic field vector points at a given location, and not the direction of the magnetic pole from that point.
WJB
CC BY-SA 4.0
2023-05-29T20:57:14.913Z
2023-05-29T20:57:14.913Z
bugmenot123
<p>You seem to think that the Earth's magnetic field should be, in some sense, smooth?</p>
<p>It's not.</p>
<p>It approximates to a solenoid field. But it's not generated by electrical currents moving in a solenoid. It's (probably) generated by convection currents driven by density moving conducting fluids through an existing magnetic field (itself generated by the movement of the adjacent cells of the core).</p>
<p>It may be helpful to consider the magnetic fields of Uranus and Neptune. They too are &quot;approximately&quot; solenoidal, and are probably formed by the same process as in Earth (but different materials). But the pseudo-solenoidal field of Uranus is inclined at ~59° to the rotation axis (compared to Earth's ~20°) and is &quot;centred&quot; 1/3 of the way from the core to the south pole. It's no where near symmetrical to the planet. Neptune is worse - it's magnetic &quot;centre&quot; is over half-way from the core to the surface, and not anywhere near the rotation axis. And it's inclined at ~47° to the rotation axis that it's not on.</p>
<p>Compared to those, Earth's field is reasonably well behaved. The biggest (and most variable, within human lifetimes) anomaly is the &quot;South Atlantic Anomaly&quot;, which <em>may</em> indicate the location of a rising plume in the core. But that's far from agreed.</p>

CC BY-SA 4.0
2023-07-12T11:47:16.943Z
2023-07-12T11:47:16.943Z
Rockdoctor
<p>Here's a global map of magnetic declination:
<a href="https://i.sstatic.net/YLA6v.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/YLA6v.png" alt="enter image description here" /></a>
How can there be zero magnetic declination in places where the magnetic and geographic poles don't line up (which is only at approx. latitude 0 and 180 for the northern hemisphere)? And why are the lines so crooked?</p>

CC BY-SA 4.0
2023-05-30T03:02:48.130Z
This seems more like a topic for [earthscience.se] than GIS SE as it isn't GIS-centric.
Vince
CC BY-SA 4.0
2023-05-30T09:00:03.047Z
May be helpful to folks/informative to give the link/source for the graphic?
JeopardyTempest
CC BY-SA 4.0
2023-05-30T17:15:19.913Z
@JeopardyTempest https://en.wikipedia.org/wiki/Earth%27s_magnetic_field
new editor
<geomagnetism>
How can there be zero magnetic declination in places where the magnetic and geographic poles don't line up
new editor
# How can there be zero magnetic declination in places where the magnetic and geographic poles don't line up

(Asked by: username_0 on 2023-05-29)

Here's a global map of magnetic declination:
[![enter image description here](https://i.sstatic.net/YLA6v.png)](https://i.sstatic.net/YLA6v.png)
How can there be zero magnetic declination in places where the magnetic and geographic poles don't line up (which is only at approx. latitude 0 and 180 for the northern hemisphere)? And why are the lines so crooked?

**Tags:** geomagnetism

> **Comments:**
> **username_1**: This seems more like a topic for [earthscience.se] than GIS SE as it isn't GIS-centric.  
> **username_2**: May be helpful to folks/informative to give the link/source for the graphic?  
> **username_0**: @username_2 https://en.wikipedia.org/wiki/Earth%27s_magnetic_field  

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## 3 answers

### Answer by username_3 on 2023-06-24. Score: 2 | Accepted answer

Consider, instead of looking at an Earth map of Magnetic Declination, looking at a map of the Earth's magnetic field:

[![enter image description here](https://i.sstatic.net/37I1k.gif)](https://i.sstatic.net/37I1k.gif)

Now trace a line across North America in such a way as to intersect the magnetic lines at locations where they are perpendicular to true north. You should end up tracing out the green line in the image posted in the question.

Read on if that sounded confusing: Instead, find and circle the points on the lines in the map of the Earth's magnetic field where the curve of the line is perpendicular to an imaginary line drawn from the true North Poll to that point. When done, the points should all be on the green lines in the map in the posted question above.


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### Answer by username_4 on 2023-05-29. Score: 3

A pole is a point. If you have two points then there are places where they line up if you'd look towards them.

For the geographic and magnetic poles we use "declination" to describe the angle between the direction towards geographic north versus the angle that the magnetic compass needle points to.

If you are in a place where both line up, then the declination is 0°.

Plotted on map those places form crooked lines because there is [geographic variation in Earth's magnetic field](https://en.wikipedia.org/wiki/Earth%27s_magnetic_field#Geographical_variation).

> **Comments:**
> **username_0**: Please read the question carefully before attempting to answer. I made it now clearer with my edit.  
> **username_4**: What is wrong with my answer?  
> **username_0**: You explained that "there are places where they line up if you'd look towards them". I know that. And that should be only in two lines of longitude - approx. 0 and 180. But on the map there are many different locations **where** they don't line up which also have zero declination. And that's my question.  
> **username_4**: They line up in those places because of variation in the magnetic field as I said. Lining up means the direction of the "magnetic needle" and geographic north here, not against the *geographic* location of the magnetic pole.  
> **username_5**: @username_4 is spot on here - the magnetic field varies geographically and the magnetic dip poles are not symmetrically opposite each other across the globe.   Declination is the angle between geographic north and the local direction of the magnetic field, which is the direction in which the horizonal part of the magnetic field vector points at a given location, and not the direction of the magnetic pole from that point.  

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### Answer by username_6 on 2023-07-12. Score: 2

You seem to think that the Earth's magnetic field should be, in some sense, smooth?

It's not.

It approximates to a solenoid field. But it's not generated by electrical currents moving in a solenoid. It's (probably) generated by convection currents driven by density moving conducting fluids through an existing magnetic field (itself generated by the movement of the adjacent cells of the core).

It may be helpful to consider the magnetic fields of Uranus and Neptune. They too are "approximately" solenoidal, and are probably formed by the same process as in Earth (but different materials). But the pseudo-solenoidal field of Uranus is inclined at ~59° to the rotation axis (compared to Earth's ~20°) and is "centred" 1/3 of the way from the core to the south pole. It's no where near symmetrical to the planet. Neptune is worse - it's magnetic "centre" is over half-way from the core to the surface, and not anywhere near the rotation axis. And it's inclined at ~47° to the rotation axis that it's not on.

Compared to those, Earth's field is reasonably well behaved. The biggest (and most variable, within human lifetimes) anomaly is the "South Atlantic Anomaly", which *may* indicate the location of a rising plume in the core. But that's far from agreed.


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