'Three norths' alignment about to end

(spatialsource.com.au)

82 points by altilunium44 days ago

4 comments

bjackman37 days ago
The title is written specifically for UK readers, the actual subject is about the point of alignment leaving GB.(Also for anyone who was confused by this, it's not about the poles, it's about the point where the bearings for all three norths are equivalent. So a "compass" would point in the same direction regardless of what kind of north it reported. Took me a moment to understand!)
- MadnessASAP37 days ago
 To clarify, it was an alignment of True, Magnetic, and Grid North. It was occurring at a point that happened to occur in England and was travelling slowly North for the past few years and now exists over water.Magnetic North is the direction a compass points in a particular location and moves with shifts in earths magnetic field as well as local anomalies.True North is parallel to the axis of Earths rotation and moves as earth wobbles and sways like a slightly unbalanced spinning top.Grid North is perpendicular to lines of Longitude which is "fixed" to a given geographic reference frame. For the UK that would be OGSB36, GPS uses WGS84, other countries may adopt different systems.All this means that an alignment of all 3 norths can occur at multiple places on earth or none at all.
- louthy37 days ago
 > The title is written specifically for UK readersIs it? The `.au` TLD might suggest otherwise.
 - LeifCarrotson37 days ago
 Not having thought about it too hard, if the three norths all align at -2 degrees west longitude, wouldn't they also be aligned at 178 degrees East longitude, somewhere near the east coast of New Zealand?Do the analogous "three souths" also have an alignment, and is it precisely opposite the north poles?
 - Majromax37 days ago
 > Not having thought about it too hard, if the three norths all align at -2 degrees west longitude, wouldn't they also be aligned at 178 degrees East longitude, somewhere near the east coast of New Zealand?There is no required equivalent 'three souths' alignment because the Earth's magnetic field is not a pure dipole. Higher-moment variations can cause essentially arbitrary (but small) deviations of magnetic north/south from its dipole approximation.
 - MangoToupe37 days ago
 True. There may be australians interested in other otherwise-obscure islands
lrasinen37 days ago
For most of Great Britain, the grid north differs from true north because the grid cells are fixed size, so they "fan out" compared to longitude lines. The exception is the 2°W meridian where the grid lines up.The magnetic north wanders around, and it now happens to match along the 2° meridian.But really the article is a year early, as the alignment point should make a brief landfall in Scotland late next year (which the article acknowledges later on). Or perhaps they expect Scotland to secede before that.
oersted37 days ago
> when the true, magnetic and grid norths met in the village of Langton Matravers in DorsetLove that, sounds like something Douglas Adams or Terry Pratchett would write :)
- dave1010uk37 days ago
 Langton Matravers is about 2km north of the coast. The 3 norths will have met land at a place called Dancing Ledge, at about SZ 00000 76833 (50.59121, -2.00000).<a href="https://en.wikipedia.org/wiki/Dancing_Ledge" rel="nofollow">https://en.wikipedia.org/wiki/Dancing_Ledge</a>The quarry caves at Winspit are worth an explore if you're in the area - they've been used in the set for Dr Who, Blake's 7 and Andor.<a href="https://en.wikipedia.org/wiki/Winspit" rel="nofollow">https://en.wikipedia.org/wiki/Winspit</a>
- rwmj37 days ago
 Langton is obviously "long town", but Matravers is a very strange non-English sounding name, and indeed according to Wikipedia it's from French: <a href="https://en.wikipedia.org/wiki/Langton_Matravers#History" rel="nofollow">https://en.wikipedia.org/wiki/Langton_Matravers#History</a>
 - antonvs37 days ago
 Town names in England are full of historical quirks that don’t sound like modern English - try browsing a map, it’s fun. Some of its place names are thousands of years old.Even names that seem very English now, like “York”, only seem that way because of their long historical presence. The town of that name started out around 70 CE as the Roman fortress Eboracum, which was a Latinized version of a Celtic name.Later, around 600 CE, the Anglo-Saxons reinterpreted the name as Eoforwic, because “eofor” meant “boar” in Old English, although the earlier name had nothing to do with boars, other than sounding similar.Then the Vikings came along in the 860s and called it Jórvík, an Old Norse adaptation of Eoforwic.Around 1000 CE, after the Norman conquest, the name was shortened to York. That has no meaning in English, other than the place name and its derivatives. Fundamentally, it’s no more or less English than Matravers.
 - louthy37 days ago
 I've just bought a house in Alderwasley in Derbyshire, the nearest town is Wirksworth [1]. I assumed that, because this area was the heart of the industrial revolution [2], the town was an eponymously named workers town built for mill workers (there are actually entire towns in the area that were built for mill workers).Then I read the history on wikipedia:The name was recorded as Werchesworde in the Domesday Book of 1086 A.D. Outlying farms (berewicks) were Cromford, Middleton, Hopton, Wellesdene [sic], Carsington, Kirk Ireton and Callow. It gave its name to the earlier Wirksworth wapentake or hundred. The Survey of English Place-Names records Wyrcesuuyrthe in 835, Werchesworde in 1086, and Wirksworth(e) in 1536.The toponym might be "Weorc's enclosure", or "fortified enclosure".I just love how place names in the UK have evolved.[1] <a href="https://en.wikipedia.org/wiki/Wirksworth" rel="nofollow">https://en.wikipedia.org/wiki/Wirksworth</a>[2] <a href="https://en.wikipedia.org/wiki/Cromford_Mill" rel="nofollow">https://en.wikipedia.org/wiki/Cromford_Mill</a>
 - antonvs37 days ago
 I agree, it's fascinating. I've lived in four countries, including England and the US, but I haven't seen anything quite like the UK names elsewhere. You do see a lot of indigenous names in the US, but they haven't evolved in the same way, probably largely because it's all so much more recent, but also because there was only one really one actual invasion, not waves of them coming from all different directions - Beakers, Celts, Roman, Norse, Anglo-Saxon, Norman.> I've just bought a house in Alderwasley in DerbyshireCongratulations! A quick check of the map shows you're right near Whatstandwell, Nether Heague, Shottle, Hognaston, and of course Knockerdown. It all makes Tolkien and Pratchett seem a bit unimaginative!
 - jaapz36 days ago
 Placenames like that really tickle meSome dude name Weorc built a small fortified homestead somewhere ages back, and here we are still using his name to refer to that same placeIt really blows my mind
 - dspillett37 days ago
 There are a lot of French influence in England's place names (and the language in general) from the couple of centuries after 1066 when the Normans ruled the roost.
 - jfengel37 days ago
 The Normans still rule the roost. The dynasty name changes every so often but King Chuck 3 can trace his line straight back to William the Bastard.
 - umanwizard37 days ago
 Charles doesn’t “rule the roost” in any meaningful sense. Who knows whether Keir Starmer descends from Normans, but his predecessor certainly doesn’t.
 exe3437 days ago
 Hey now, at least Rishi was elected to rule Britain - the old lady Vicky wasn't remotely connected to India but she was still Empress.
 jfengel37 days ago
 I don't think India had a democracy before the Brits, either.Not that it gives anyone else the right to come in and declare themselves Raj. But Vicky wasn't the first to come to India and declare themselves in charge.
 - MangoToupe37 days ago
 > Langton is obviously "long town"Are we speaking another language? C'mon, this isn't obvious at all.> but Matravers is a very strange non-English sounding name, and indeed according to Wikipedia it's from FrenchDuh? Was "vers" not a major clue?...what kind of language education did you receive? I was taught english, french, and latin. Were you taught german or dutch by any chance?
skrebbel37 days ago
How can "north" be a place? I feel like they forgot to add the content.
- oersted37 days ago
 I agree, but the video at the bottom helped.You can draw a line between your location and the north pole, they talk about three variants:- Magnetic North: Shortest surface line to the magnetic north pole (simply in the direction of the compass at your location).- True North: Shortest surface line from where you are to the geographic north pole (based on the rotation axis?).- Grid North: A line to the same geographic north pole, but aligned to the longitude lines (EDIT: for a local UK grid standard, slightly different from the global one). I didn't fully understand the subtleties of why it's different from True North, something about the projection. Not sure if it's exactly to the same north pole, the rotation axis might also change slightly and I assume that the grid north point is fixed by convention?They are saying that there's a particular point where all three lines point in the same direction, and that point is moving.
 - chippiewill37 days ago
 In the UK there's a standard grid used for local-only mapping: <a href="https://en.wikipedia.org/wiki/Ordnance_Survey_National_Grid" rel="nofollow">https://en.wikipedia.org/wiki/Ordnance_Survey_National_Grid</a>It's a transverse mercator projection rather than a mercator as you might often see because it minimises distortion over the UK as a whole which means that the distortion is as you move away from the meridian, rather than as you move away from the equator (with a regular mercator I think all points have the grid aligned with true North)This grid is setup such that it's origin is not on the prime meridian (at Greenwich), but 2deg west so only points on the line 2deg west are aligned with true north.
 - gonzus37 days ago
 One of the advantages of doing this seemingly weird projection is that you can treat "local" maps (for some definition of local) as flat rectangular grids without introducing a lot of errors: drawing straight lines between two points, measuring the distance / angle between them, etc., just by dealing with a flat piece of paper. VERY convenient, but the farther you are from the center of the projection, the higher the errors that are introduced.
 - Sharlin37 days ago
 In short, you can treat the local geometry as Euclidean.
 bregma37 days ago
 Or, to put it simply, the shape of the Earth can be considered flat for local mapping purposes.If grid north and true north are the same everywhere, it would be proof the entire Earth is flat.
 tialaramex37 days ago
 If your planet is tiny, it's very easy to figure out that it's a ball, a child can see it with their bare eyes. The planets in "Outer Wilds" are like that.Because this planet is larger, smart people trying to figure out how it works used simple tools and measurements to conclude that it's a ball, we know that Greeks and Romans figured this out, I'm sure other civilisations did too.Greg Egan's "Incandescence" has people who live somewhere where you can discover, in this same way, General Relativity. There's a small but noticeable difference between the simple linear results we'd see for Newtonian physics in rudimentary experiments and what they can observe and they figure out why. Since they have no context for what it means to observe this and have (to their memory) always lived somewhere this happens, they aren't terrified by this discovery any more than we were terrified to discover how our Sun must work - so much hydrogen in one place that it undergoes spontaneous nuclear fusion which releases so much energy that we can easily see by it even after it is no longer directly visible, OK cool, I still need groceries.
 teamonkey37 days ago
 It’s easy to see that the surface of the earth is a ball - or at least a curved surface - simply by going to the seaside and watching ships dip below the horizon before they fully disappear.The ancient Greeks proved it was a ball and measured the dimensions of it using mathematics, but the concept of a curved earth was known to seafarers long before that.
 - Luc37 days ago
 > Magnetic North: Shortest surface line to the magnetic north pole (simply in the direction of the compass at your location).Magnetic North is the local horizontal direction of the magnetic field. But that doesn't generally coincide with the shortest surface line (geodesic) to the magnetic north pole (however you define that - there's several).If you followed your compass you could end up in a loop without reaching the magnetic north pole.
- rcxdude37 days ago
 This video explains it a lot better: <a href="https://www.youtube.com/watch?v=HcFvegnQpPo" rel="nofollow">https://www.youtube.com/watch?v=HcFvegnQpPo</a>Basically, there's a "true north" which is where the axis of rotation of the earth intersects with its surface, and for local mapping in the UK there is a grid which is not longitude and latitude but instead locally flat (i.e. each grid square has the same area) but that means that it only lines up with true north along one line that goes north-south through roughly the middle of the UK.Then the third is magnetic north, and this is one that both varies from place to place and with time. Magnetic north, as in the place where the earth's magnetic field intersects with its surface, doesn't necessarily line up with true north. Even more complicatedly, compasses don't actually point to the magnetic north pole, but can be about ten degrees off to the east or west depending on where you are on the planet's surface (for most of the surface. Near the poles it can be wildly off. Obviously if you're walking around near magnetic pole your compass is going to be all over the place). And to top it all off, this changes from year to year. If you have charts for navigating by compass, it will give you a table and formula for correcting what you read on your compass to grid or true north, and those depend on the date. This also needs to be kept up to date with an almanac or similar because it can't be predicted arbitrarily far into the future.What this means, is that there's basically a funny-shaped line on the earth's surface where the magnetic north happens to line up with the true north, and this line moves over time (you can see a current map here: <a href="https://www.ncei.noaa.gov/sites/default/files/inline-images/D.jpg" rel="nofollow">https://www.ncei.noaa.gov/sites/default/files/inline-images/...</a>). At the moment, this line intersects with the line where the UK's grid north and true north line up within the UK mainland, but it's been moving for the past three years and this intersection point will soon be off the coast.
- jstanley37 days ago
 If the shortest route from your current location to the English channel crosses the M4 then you're in the north, otherwise you're not.
 - teamonkey37 days ago
 Anything outside the M25 is “The North”, regardless of latitude.
- x3n0ph3n337 days ago
 I think they are referring to a moving point on earth's surface where all 3 norths appear to be in the same direction. I agree it wasn't clear.What's also unclear to me is how all 3 could reliably be colinear, but maybe it's an aspect of spherical geometry that eludes me.
 - tor825gl37 days ago
 The locus of points where magnetic north aligns with true north is a (one dimensional) curve. On one side of the curve magnetic north is too far to the east, on the other side too far to the west.Same for the locus of points where grid north matches true north.The two curves meet in some finite number of isolated points, at each of these all three directions are the same.