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Grid, Magnetic and True north allign at Langton Matravers. And the alignment will stay somewhere in the UK for 3 years or so. No more faff with adding or subtracting for a while.
27
In reply to annieman:
Hadn't seen that one. Though the difference between the grid and magnetic norths has been so small, especially towards the west of the UK, for a while now that adding or subtracting hasn't been worth doing.
Dave
9
In reply to Tringa:
> Hadn't seen that one. Though the difference between the grid and magnetic norths has been so small, especially towards the west of the UK, for a while now that adding or subtracting hasn't been worth doing.
I suspect this is going to result in future problems as a whole generation of people won't be used to doing this (even if they're taught).
9
3
In reply to annieman:
"This is not related to climate change" LOL
9
In reply to annieman:
I’m struggling with this, surely anywhere on that grid line of longitude grid and true will be always in agreement as neither change. Furthermore if magnetic agrees with grid and true at that village it will also agree anywhere North or South of that.
When magnetic north moves off that grid line the three Norths will no longer have a point of agreement.
What am I missing?
2
1
In reply to ablackett:
> I’m struggling with this, surely anywhere on that grid line of longitude grid and true will be always in agreement as neither change.
Yes
> Furthermore if magnetic agrees with grid and true at that village it will also agree anywhere North or South of that.
No, because magnetic varies with where you are on the earth.
>
> When magnetic north moves off that grid line the three Norths will no longer have a point of agreement.
According to the article (link in there somewhere). The conjunction moves slowly north, reaching Fraserburgh in 2026!
Post edited at 13:09
2
In reply to MG:
via Hebden Bridge
2
In reply to ablackett:
> I’m struggling with this, surely anywhere on that grid line of longitude grid and true will be always in agreement as neither change.
I thought that would vary, as longitude lines converge at the true poles and factor in the earth's curvature, whilst OS Grid is a 2D projection with square, rather than curved grid lines. If you move north or south along that line of longitude the variance between grid and true will change. (It's printed on the OS sheets and will vary by location). They must always be aligned in that particular location though.
> Furthermore if magnetic agrees with grid and true at that village it will also agree anywhere North or South of that line.
IIRC magnetic north is currently somewhere north of Canada (?) so the grid magnetic angle will vary with both latitude and longitude.
(Captain Paranoia will be along soon to correct my schoolboy errors)
Post edited at 13:32
6
In reply to magma:
> via Hebden Bridge
It'll get caught up in all the Dream Catchers in Hebden Bridge and be trapped there.
13
In reply to Ridge:
this may explain? youtube.com/watch?v=Gea4cEA5Ris&
In reply to annieman:
You can now just get out of the tent in Tom’s Field and head South for Dancing Ledge without the need to get the compass out…great news 😀
5
In reply to Ridge:
> They must always be aligned in that particular location though.
Langton happens to fall on the 2 degree west meridian. Which is the false origin for OSGB grid (I know the area very well, and had noted that little nugget with DofE groups). Therefore, grid N is always aligned with True N along the 2 degree W meridian.
As others have noted, magnetic N varies with location on the globe. It just happens that the local magnetic N in Langton is currently also aligned with True/Grid N.
I noted a sense of the reporter not really understanding what they were writing about; especially the 'global warming' bit...
9
In reply to annieman:
https://publicnewstime.com/science-news/true-north-magnetic-north-and-grid-...
that gives a lot more detail, the thing I was missing was that mag north line is curved, I assumed it would be straight.
In reply to ablackett:
> the thing I was missing was that mag north line is curved, I assumed it would be straight.
See if you can find a global declination map; it varies and wanders about all over the place. It's between 35° and 45° in New Zealand. The Earth's magnetic field is pretty wacky...
Like this map: see the declination historically, too...
https://www.ncei.noaa.gov/maps/historical_declination/
Post edited at 20:53
3
In reply to captain paranoia:
> It's between 35° and 45° in New Zealand.
d'oh! I originally put 25°, because that's what I remembered. But then I read the numbers off the map. But I read the location coordinates, not the declination. Which varies 20° to 25°.
In reply to annieman:
I was obvious the Square and Compass always was the most important place on Earth really.
10
In reply to Pedro50:
> "This is not related to climate change" LOL
It is a very average piece of journalism by someone who doesn't understand maps or earth sciences. A good picture or diagram really would have helped. Magnetic north isn't wandering either, it's a pretty steady line, having tracked westwards to around 70degree mark then around the mid 1800s started back eastwards, as it nearers the pole the annual change has increased. How could anyone who loves or knows maps have missed a chance to throw in the words graticule intersection into an article!
3
In reply to Toerag:
> I suspect this is going to result in future problems as a whole generation of people won't be used to doing this (even if they're taught).
I suspect that there are just as many current day problems due to people applying the magnetic variation that they were taught when they learned how to use a compass.
5
In reply to annieman:
Perhaps a better version of the story, with an appropriate diagram, from The Metro here: https://www.msn.com/en-gb/news/world/historical-alignment-over-britain-as-t...
Pedantic input from me (I have to grapple with these issues when drawing orienteering maps): Surely the Square and Compasses, excellent as it is, is in Worth Matravers, not Langton Matravers? Grid North at Worth Matravers is 0.03 degrees west of True North and always will be. The only locations where the Three Norths can align are on the -2 degree meridian where Grid and True North are co-incident. The Metro article explains how Magnetic North will also align, in a grand triple alignment, at different points on that meridian over the next few years, starting close to The Spook (E1 5b) this weekend. Anyone up for it?
Martin
4
In reply to Martin Hore:
>The Metro article explains how Magnetic North will also align, in a grand triple alignment, at different points on that meridian over the next few years, starting close to The Spook (E1 5b) this weekend. Anyone up for it?
And you'll have another chance at Alcove Crack (HVS 5a) sometime late next year or early 2024.
In reply to timjones:
> I suspect that there are just as many current day problems due to people applying the magnetic variation that they were taught when they learned how to use a compass.
Or when they cant be arsed to replace that old map since after all the key features havent moved.
In reply to annieman:
Wonderful news, yet another Brexit benefit. Rees-Mogg was right all along. 😉
2
In reply to mondite:
> Or when they cant be arsed to replace that old map since after all the key features havent moved.
How do you mean? That's true isn't it!?
In reply to ablackett:
> I’m struggling with this, surely anywhere on that grid line of longitude grid and true will be always in agreement as neither change. Furthermore if magnetic agrees with grid and true at that village it will also agree anywhere North or South of that.
>
> When magnetic north moves off that grid line the three Norths will no longer have a point of agreement.
> What am I missing?
I am struggling with this too. Grid and true don't move relative to each other. So this "magical" line has to be the existing alignment of grid and true (2deg W of Greenwich).
The OS video doesn't show alignment, it shows intersection of 3 lines at different angles.
What is happening is a progression of the true and mag north alignment along a line roughly aligned with grid North - true north line.
Finally, what is harder to grasp is why a magnetic north - true north alignment at one point on a line of longitude is not alignment at all points of that line of longitude.
Post edited at 07:58
In reply to mondite:
> Or when they cant be arsed to replace that old map since after all the key features havent moved.
Magnetic north was about 9 degrees out from grid north when I learnt. We could have a game if, when did you learn to use map and compass…
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In reply to annieman:
2019 blog from Ordnance Survey
https://www.ordnancesurvey.co.uk/newsroom/blog/magnetic-north-continues-its...
Plus a British Geographical calculator to calculate difference between grid and magnetic for where you are
http://www.geomag.bgs.ac.uk/data_service/models_compass/gma_calc.html
1
In reply to Philip:
> Finally, what is harder to grasp is why a magnetic north - true north alignment at one point on a line of longitude is not alignment at all points of that line of longitude.
Crudely, the directon of magnetic north varies depending where you are and with time, so it's only at one spot at any one time where it will align with true north. As it happens, this is on 2 Deg W in the near future. Whether it moving "up" 2 Deg W for a while is coincidence, is a question.
In reply to annieman:
Don't tell anyone but I've been ignoring the difference for a while and still only get lost the average amount.
4
In reply to annieman:
French maps such a pleasure. The grid is true. And the refs are gps numbers. Also integrates with latitude.
3
In reply to Philip:Because the magnetic field is messy. It seems to have 2 North poles if you explore that link above, no idea why this would be the case, but I would guess it's all to do with the convection currents of the mantle. So as you go North, the influence of the 'other' North pulls the declination away from the true North line. I was as confused as you a couple of days ago, but this makes more sense to me now.
> The OS video doesn't show alignment, it shows intersection of 3 lines at different angles.
I'm not sure which video you mean, but if it is using the same sort of diagram as the link posted up thread.
https://www.ncei.noaa.gov/maps/historical_declination/
The lines on the map, don't show the direction of the magnetic north, they show a line on which the declination is x deg, kind of like iso-bars.
> Finally, what is harder to grasp is why a magnetic north - true north alignment at one point on a line of longitude is not alignment at all points of that line of longitude.
In reply to ian caton:
> French maps such a pleasure. The grid is true.
True? As in a pure lat/long grid, aligned to true North?
I can see a number of reasons why that wouldn't be a pleasure for me.
That will be rubbish for measuring distances by counting grids, as the grid spacing will vary with position. And you still have to account for variable declination, as the grid is static, but magnetic N is not. And the grid lines on a projected map must be curved, if they are true grid. The latitude parallels will be, well, parallel, and therefore straight, but their spacing will vary.
3
In reply to steveriley:
What's "the average amount", Steve?
In reply to jpicksley:
50th centile, I thought you were good at maths?
4
In reply to ablackett:
I'm not confused, the post I replied to had the confusion.
In reply to ablackett:
> I’m struggling with this, surely anywhere on that grid line of longitude grid and true will be always in agreement as neither change. Furthermore if magnetic agrees with grid and true at that village it will also agree anywhere North or South of that.
>
> When magnetic north moves off that grid line the three Norths will no longer have a point of agreement.
> What am I missing?
If I read it correctly then the article states it's the first point/ Village where the alignment comes ashore. So only one place.
Post edited at 00:19
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In reply to Ridge: I was sat here thinking there must be a witty line regarding hebden bridge hippies and this story . Well done sir .
1
In reply to mike123: we ( me and the kids ) were pondering what a compass would do if you were stood bang on the North Pole . Have a ponder before googling .
In reply to mike123:
> we ( me and the kids ) were pondering what a compass would do if you were stood bang on the North Pole . Have a ponder before googling .
At the geographic north pole, there's not really a problem. the compass will, as always, point in the direction of the earth's magnetic field which will be roughly towards the magnetic north pole - some hundreds of kilometres distant.
At the magnetic north pole itself, the compass will try to point vertically downwards.
In most places in the northern hemisphere the compass will try to point a little downwards, hence why most compasses are weighted to offset this, and why you can buy southern hemisphere compasses with the opposite balancing weight.
Martin
2
In reply to BuzyG:
> If I read it correctly then the article states it's the first point/ Village where the alignment comes ashore. So only one place.
A Blackett answers his own question in his post at 19.56 on Wednesday with a useful link. The triple alignment point does move north across Britain, starting about now at The Spook (E1 5b) reaching Alcove Crack (HVS 5a) late next year or early 2024 (as per my earlier posts) and then passing through Grassington, out into the North Sea at Berwick Upon Tweed and meeting land again - briefly - just north of Aberdeen. (All points on the 2 degrees west meridian where the OS easting is 400,000.)
Martin
In reply to captain paranoia:
> > French maps such a pleasure. The grid is true.
> True? As in a pure lat/long grid, aligned to true North?
> I can see a number of reasons why that wouldn't be a pleasure for me.
> That will be rubbish for measuring distances by counting grids, as the grid spacing will vary with position. And you still have to account for variable declination, as the grid is static, but magnetic N is not. And the grid lines on a projected map must be curved, if they are true grid. The latitude parallels will be, well, parallel, and therefore straight, but their spacing will vary.
Agreed. I'm pretty sure French maps use the UTM (Universal Transverse Mercator) grid projection. This has the advantage over our OS Grid in that it's applicable and used worldwide, and it's a little easier to transform from UTM to geographical Lat/Long and vice-versa. But using UTM does not produce grid lines parallel to true north across the projection. This is impossible if you want equally spaced parallel grid lines as the "captain" has explained.
If you want, you can check this using Google Earth in "view"/"grid" mode (I just did). Zoom in to a point (your house should do, but equally anywhere in the world) and read its Longitude and UTM easting. (You can toggle these in "tools"/"options"). Then zoom in to a place on the same line of longitude but a few hundred km north. The UTM easting will be different. The only places where you don't see this are on - or close to - the central meridians of the UTM zones. These are 3 degrees east for UTM zone N31 (Eastern England and much of France) and 3 degrees west for UTM zone N30 (the rest of Britain). For comparison, the OS grid fixes its grid north to true geographic north at 2 degrees west and also differs from UTM in other respects - notably the way it approximates the shape of the earth.
Martin
In reply to jpicksley:
You cheeky little monkey, you know what I mean. What's the actual number? Where are your statistics? I want proof, I want evidence, not your throw away lines. That's what's wrong with society. Anecdote supercedes evidence.
2
In reply to annieman:
If there was any justice, it would have been Worth Matravers, specifically the beer garden of the Square & Compass.
4
In reply to captain paranoia:
Bugger all difference at the scale of a standard map.
In reply to Toerag:
> I suspect this is going to result in future problems as a whole generation of people won't be used to doing this (even if they're taught).
Can confirm as a young whippersnapper none of us know anything about this, and it's going to require some major re-adjustment later on
1
In reply to ian caton:
> Bugger all difference at the scale of a standard map.
Difference in what, exactly? The curvature, granted.
But if the grid is a regular submultiple of an angular measure, then the vertical grid spacing will not be uniform, because longitude meridian lines get closer as you approach the poles.
If you want the grid spacing to be consistent across the entire mapping region, then it cannot be a regular angular spacing, so it makes it difficult to read angular measure off the map, which somewhat defeats your 'benefit'.
Of course, the IGN aren't that daft. So they use a UTM projection (as Martin suggested), using the UTM zone appropriate to France. And apply a 1km grid, so you can measure distances. But they also print a completely separate 5' lat/long grid (representing 'true north grid'). But you still have to deal with magnetic north.
https://www.stanfords.co.uk/France-IGN-25K-TOP25S%C3%A9rie-Bleue-Topographi...
UTM is the same projection as OSGB, except with different zone origins, and different geoid model. The UTM zones overlap. A place in the overlap will have different UTM coordinates in each zone, so it it essential to specify the zone you are referring to.
https://www.stanfords.co.uk/France-IGN-25K-TOP25S%C3%A9rie-Bleue-Topographi...
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