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Magnetic north

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 Flinticus 21 May 2020

Reading up on navigation. Got an old book from a charity store. Published in 1986 and mine is a reprint from 96. 

It says that magnetic north will be west of grid north for many years to come...

Yeah, well those years have come and now its actually east in parts of the UK and moving east very gradually across the rest. According to the OS mag and grid north are virtually the same thing in Glasgow at this time.

That 'add to mag, rid to grid' now does not hold true in some parts of the UK for the first time (from 2014) since 1660s!

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 wintertree 21 May 2020
In reply to Flinticus: What maps don’t tell you is that it’s actually a magnetic south pole, hence the north pole of magnets pointing towards it.  Major historical naming error.

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 Basemetal 21 May 2020
In reply to wintertree:

Isn't the red end of a compass needle properly called a ' north seeking pole'?

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 wercat 22 May 2020
In reply to Basemetal:

or North Indicating?

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 deepsoup 22 May 2020
In reply to wercat:

> or North Indicating?

If you like, but the "North" or "North seeking" or whatever-you-want-to-call-it end of a compass needle is attracted to the South pole of a magnet. 

So if you want to think of the Earth as a magnet, it has its South pole somewhere up near the North Pole and vice versa.

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 Red Rover 22 May 2020
In reply to wintertree:

So that means Yorkshire is in the south of England?! I'm not sure I can cope with this! 

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 mypyrex 22 May 2020
In reply to Flinticus:

> Reading up on navigation. Got an old book from a charity store. Published in 1986 and mine is a reprint from 96. 

> It says that magnetic north will be west of grid north for many years to come...

> Yeah, well those years have come and now its actually east in parts of the UK and moving east very gradually across the rest. According to the OS mag and grid north are virtually the same thing in Glasgow at this time.

But surely if it's been moving west for so long it will eventually end up somewhere which is actually regarded as being east of us! Hang on, I'll check that out with Trump ;o)

Post edited at 10:04
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 Jamie Wakeham 22 May 2020
In reply to deepsoup:

Exactly so.  The geographic north of the earth behaves as if there is a magnetic south up there, and that's why the north of a compass (or any other magnet) is attracted towards it.

The whole 'north-seeking' idea is, I think, a confusion that's been introduced by people who don't understand that the geographic north is a magnetic south, and they choose to believe instead that the compass is secretly polarised the other way around - ie the red end is actually a south.  But we always call it the north end, so they started to call it the 'north-seeking' end.  I have actually seen this version being taught by a primary teacher once.

It can be disproved by looking at how a compass behaves near a magnet of known polarity, or by doing a practical using Fleming's laws to define the direction of the field.  Of course, if you forget that Fleming was using conventional current then you'll get exactly the wrong answer...

(Edited to concur with John's point below; just saying that the mag south is at the north pole is a significant simplification)

Post edited at 10:39
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In reply to deepsoup:

There is not a South (magnetic) pole somewhere up near the North pole and vice versa. The Earth's magnetic field is generated in the molten iron and nickel outer core, which behaves as a dipole with its southern magnetic pole directed upwards, roughly towards the rotational north pole. So the magnetic south pole is somewhere near the core/mantle interface.

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 deepsoup 22 May 2020
In reply to John Stainforth:

> There is not a South (magnetic) pole somewhere up near the North pole and vice versa.

I didn't say there is.  I said that's which way round it would be if you want to think of the earth as a giant magnet.

> which behaves as a dipole with its southern magnetic pole directed upwards

To a first order approximation cleverclogs, so don't be coming on here giving me a bollocking for lacking nuance and presenting slightly more nuance as if that's the absolutely bang-on deffo the right answer.  For anyone who's interested there's plenty to read about it if they just pop off to wikipedia. 

(That's where I'm cribbing this from, I don't actually know anything obviously.)

And which way is "upwards" anyway, since we're being wildly pedantic now?  If you happen to be at the centre of the Earth, Yazz and the Plastic Population would literally* be right.  (*NB: the word "literally" may sometimes now literally mean "figuratively" - see OED for details.)

Why are all the spaceships in all the Star Trek spin-offs always the same way up when they bump into each other deep into interstellar space?

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 Basemetal 22 May 2020

No worse than the initial positive  notion of the flow of electricity that resulted in designating electrons as being negatively charged I suppose

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 GrahamD 22 May 2020
In reply to deepsoup:

> Why are all the spaceships in all the Star Trek spin-offs always the same way up when they bump into each other deep into interstellar space?

So the crews don't have to Klingon?

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 Jamie Wakeham 22 May 2020
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 DancingOnRock 22 May 2020
In reply to Flinticus:

Flux Lobe Elongation. 
 

There’s probably not a single ‘north’ pole. 
 

https://www.youtube.com/watch?v=1OStKs-e_zc&

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In reply to wintertree:

> What maps don’t tell you is that it’s actually a magnetic south pole, hence the north pole of magnets pointing towards it.  Major historical naming error.

But 'North' as a concept predates the discovery and use of the magnetic compass; the four cardinal points are relative to the sun. Check the etymology of 'north'; Indo-european for 'left', and North is to our left when facing the rising sun (East).

So it's the magnetic field naming that is wrong, not the naming of the North Pole...

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 Planeandsimple 22 May 2020
In reply to Flinticus:

"Grid to mag add" is one of my pet hates. It is unnecessarily dumbing things down and downright dangerous as it encourages laziness.

Better to teach people properly the first time round. I've seen numpties walk 28 degrees in the wrong direction in featureless terrain and wonder why their GPS is "wrong". 

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 Martin Hore 22 May 2020
In reply to Planeandsimple:

> "Grid to mag add" is one of my pet hates. It is unnecessarily dumbing things down and downright dangerous as it encourages laziness.

> Better to teach people properly the first time round. I've seen numpties walk 28 degrees in the wrong direction in featureless terrain and wonder why their GPS is "wrong". 


I don't think I'm too "dumb" and I've always found "Grid to mag add" pretty useful. I have a real problem remembering which is correct when there are just two options. Little aids like that really help. Perhaps you can explain how you "teach people properly".

Martin

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In reply to Martin Hore:

The way that I teach it, until recently, is to say you are going from the 'small'map to the bigger 'landscape'so make the bearing bigger, and visa versa. For the moment I'm telling folk to ignore the variation as a bearing taken with conventional hand-held Silva compasses (perhaps the most commonly used) are usually accurate to between 2 and 4 degrees of variation.

Post edited at 20:18
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 wercat 22 May 2020
In reply to Planeandsimple:

perhaps you are just blessed with a better memory than the rest of us.  It is possible to have spent time learning stuff properly but still be forgetful.  Nothing to do with not understanding, just less than purrfect memory - hence why I always used mugs as recommended in several books I read when learning navigation.

Or perhaps another solution would be to carry a book from which to remember things correctly and get it out in bad weather and sit reading it while the map blows away?

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 Flinticus 23 May 2020
In reply to captain paranoia:

Thanks! Cool fact

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In reply to DancingOnRock:

In my undergraduate physics course we were taught that there is no such thing as a magnetic monopole anyway: magnetism arises from charge movement and relativity so the source is always something akin to a solenoid. The "poles" of a solid magnet are just where the field exits so if you are defining magnetic poles for the earth you might as well do it at the surface. If you delve deeper there will be no such thing as a pole?

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 tlouth7 23 May 2020
In reply to harold walmsley:

> The "poles" of a solid magnet are just where the field exits so if you are defining magnetic poles for the earth you might as well do it at the surface.

But then you would not be able to explain dip which is pretty important; at the very least as a reason to hold your compass horizontal.

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 mysterion 23 May 2020
In reply to captain paranoia:

> So it's the magnetic field naming that is wrong, not the naming of the North Pole...

But it's 'the Scientz'

Clap now!

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In reply to Martin Hore:

> Perhaps you can explain how you "teach people properly".

See the thread I linked earlier for a discussion of why that mnemonic is poor, and not universally applicable. And for a much simpler method for practical navigation.

https://www.ukclimbing.com/forums/hilltalk/latest_on_the_wandering_north_pole-719106?v=1#x9197300

Post edited at 12:28
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In reply to phizz4:

> The way that I teach it, until recently, is to say you are going from the 'small'map to the bigger 'landscape'so make the bearing bigger, and visa versa

Again, this is not universally applicable, and you need to muck about unnecessarily with numbers.

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In reply to harold walmsley:

The depth at which the magnetic field lines emanate from the dipole is nowhere near the surface of the Earth, but about three thousand metres down. So the magnetic field lines are strongly divergent/convergent between there and the surface. At the Earth's surface the magnetic inclination (dip of the field  lines) is everywhere pretty high, except in equatorial regions.

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 DancingOnRock 23 May 2020
In reply to harold walmsley:

Did you watch the video?

It’s believed it is the magma flow under the surface that gives rise to different magnetic regions. The fact that the needle points north is just because there’s a stronger flow of magma in Canada. There’s also strong flows elsewhere within the planet and these grow stronger and weaker. It’s all ‘tidal‘. At present the flow under Canada is weaker and the flow under Russia is getting stronger. 

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In reply to captain paranoia:

> So it's the magnetic field naming that is wrong, not the naming of the North Pole...

And the reason for that 'naming error' is that it was given that convention because of the magnetic compass, and the fact that the N pole of the compass points to the geographic North. And, since opposite poles attract, that meant that the geographic North pole is actually a magnetic South pole (according to the given convention).

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 Ridge 23 May 2020
In reply to phizz4:

> The way that I teach it, until recently, is to say you are going from the 'small'map to the bigger 'landscape'

But what if the map is close and the landscape is far away?

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In reply to DancingOnRock:

I hadn't watched the video but I have now. It makes me wonder. If the north pole is wandering due to relatively local changes in the circulations at northern latitudes does that mean there won't be similar wanderings of the south magnetic pole (weaker links to northern dipoles) and therefore that the relationship between magnetic and geographic poles is (or at least can be) different in the north and in the south? Are the two magnetic poles currently diametrically opposite each other (or whatever is the equivalent for an ellipsoid)?

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 Planeandsimple 24 May 2020
In reply to wercat:

> perhaps you are just blessed with a better memory than the rest of us.  It is possible to have spent time learning stuff properly but still be forgetful.  Nothing to do with not understanding, just less than purrfect memory - hence why I always used mugs as recommended in several books I read when learning navigation.

> Or perhaps another solution would be to carry a book from which to remember things correctly and get it out in bad weather and sit reading it while the map blows away?

Every map has the method of calculating the grid mag adjustment written on it in clear terms. You don't need a book you just need to read the bit of text by the three arrows and remember it or look back for reference, surely you know where this information is it you've been taught correctly.

If you're really struggling add a piece of masking tape to your compass and write your calculated value on it. If you adjust your map and cut it down then tape it on the back. It's really not beyond the wit of a simpleton to find an adequate work around for failing memory. 

If you can't remember a single number after you've calculated it how will you ever be able to successfully work out your speed/pacing/bearing?

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 Planeandsimple 24 May 2020
In reply to phizz4:

> The way that I teach it, until recently, is to say you are going from the 'small'map to the bigger 'landscape'so make the bearing bigger, and visa versa. For the moment I'm telling folk to ignore the variation as a bearing taken with conventional hand-held Silva compasses (perhaps the most commonly used) are usually accurate to between 2 and 4 degrees of variation.

I'm sure they will really help them in future. Navigation is a life skill applicable to anywhere in the world. I assume those who are asking you to teach them are paying you, or are looking to use the skill outside of your lesson.  In either case teach them properly. 

People remember that they are first taught I speak from experience that people who are taught to ignore it out that grid mag add is the only way are incredibly hard to re-teach because it becomes an ingrained habit after years of reinforced experience with no consequence for the error. If you only mention that something occurs, once in a while, in passing then they will not take home that bit of information. 

Teach a man to bodge and he'll always be a bodger never a master. 

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In reply to Planeandsimple:

> Every map has the method of calculating the grid mag adjustment written on it in clear terms.

I have always used, and now teach, correction based on that simple figure showing the relationship between MN and GN:

1. remember where grid N is wrt mag N (W or E, and the amount). As you suggest, you can easily mark this on the baseplate

2. remember which N we've just measured (GN or MN)

3. rotate the compass capsule to move the measured N to the other N

No need to remember mnemonics, or try to remember what they mean. Applicable anywhere in the world. You just need to know where GN is wrt MN, and rotate the capsule accordingly to move between GN and MN. No adding, no subtracting, just a simple movement of the capsule.

I also quickly explain grid divergence (can't wrap a flat piece of paper around a football), why MN moves, and use New Zealand as a good example of where GMA correction is very important.

Post edited at 13:18
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 Basemetal 24 May 2020
In reply to captain paranoia:

I've still got a Silva Type 25 that has a declination offset adjustment screw that lets you build the correction into the compass. Turning the micro-screw offsets the capsule base alignment lines from the bearing bezel by the required amount. You do this only when the deviation needs updated.

In use, you line up the grid lines on the map, and the bearing is ready for use with the needle. Works for going from sighting to plotting too.

A welcome pedagical effect of using it is that it reinforces what's actually going on with the offset .

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 DancingOnRock 24 May 2020
In reply to harold walmsley:

I think what they’re saying is it’s just coincidence that we currently have a couple of large masses close to the spin axis. 
 

It doesn’t matter where the ‘South’ parts of the fields emerge from the planet, the big ‘North’ regions are in Canada and Russia and so the overall field ’heads‘ in that direction. If those regions weaken to a point that the areas in the Atlantic are stronger then our needles will just point there. 
 

As in the video, we are seeing other planets have very complex magnetospheres. 

Post edited at 14:01
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 Planeandsimple 24 May 2020
In reply to captain paranoia:

Precisely. The information is there, read the map apply brain. As I stated earlier positive reinforcement of years of Grid to Mag laziness, long after the actual lesson on navigation was taught, has caused people I know to walk into the wrong valley on featureless south Atlantic islands.

Well done for teaching it the right way. Being an instructor myself I know how easy it is to fall into the trap of teaching to pass an assessment the real learning is not a pass or fail on a micronav. It's being able to pick up a map 30 years out of date with 50m contour intervals, thousands of miles from home and get from point a to point b when you're tired and bad weather hits. Simple shortcuts lead to simple errors. 

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In reply to Planeandsimple:

> Simple shortcuts lead to simple errors. 

The crazy thing is that rotating the capsule between the two Norths is simpler and easier than the mnemonics...

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