[HN Gopher] 'Three norths' alignment about to end
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'Three norths' alignment about to end
Author : altilunium
Score : 71 points
Date : 2025-12-24 15:17 UTC (7 days ago)
(HTM) web link (www.spatialsource.com.au)
(TXT) w3m dump (www.spatialsource.com.au)
| oersted wrote:
| > when the true, magnetic and grid norths met in the village of
| Langton Matravers in Dorset
|
| Love that, sounds like something Douglas Adams or Terry Pratchett
| would write :)
| rwmj wrote:
| Langton is obviously "long town", but Matravers is a very
| strange non-English sounding name, and indeed according to
| Wikipedia it's from French:
| https://en.wikipedia.org/wiki/Langton_Matravers#History
| dspillett wrote:
| 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.
| jfengel wrote:
| 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.
| umanwizard wrote:
| Charles doesn't "rule the roost" in any meaningful sense.
| Who knows whether Keir Starmer descends from Normans, but
| his predecessor certainly doesn't.
| exe34 wrote:
| 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.
| antonvs wrote:
| 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 Jorvik,
| 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.
| louthy wrote:
| 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] https://en.wikipedia.org/wiki/Wirksworth
|
| [2] https://en.wikipedia.org/wiki/Cromford_Mill
| MangoToupe wrote:
| > 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 French
|
| Duh? 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?
| dave1010uk wrote:
| 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).
|
| https://en.wikipedia.org/wiki/Dancing_Ledge
|
| 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.
|
| https://en.wikipedia.org/wiki/Winspit
| skrebbel wrote:
| How can "north" be a place? I feel like they forgot to add the
| content.
| x3n0ph3n3 wrote:
| 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.
| tor825gl wrote:
| 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.
| oersted wrote:
| 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.
| chippiewill wrote:
| In the UK there's a standard grid used for local-only
| mapping:
| https://en.wikipedia.org/wiki/Ordnance_Survey_National_Grid
|
| 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.
| gonzus wrote:
| 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.
| Sharlin wrote:
| In short, you can treat the local geometry as Euclidean.
| bregma wrote:
| 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.
| tialaramex wrote:
| 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.
| teamonkey wrote:
| 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.
| Luc wrote:
| > 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.
| rcxdude wrote:
| This video explains it a lot better:
| https://www.youtube.com/watch?v=HcFvegnQpPo
|
| 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:
| https://www.ncei.noaa.gov/sites/default/files/inline-
| images/...). 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.
| jstanley wrote:
| 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.
| teamonkey wrote:
| Anything outside the M25 is "The North", regardless of
| latitude.
| lrasinen wrote:
| 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 2degW meridian where the
| grid lines up.
|
| The magnetic north wanders around, and it now happens to match
| along the 2deg 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.
| bjackman wrote:
| 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!)
| louthy wrote:
| > The title is written specifically for UK readers
|
| Is it? The `.au` TLD might suggest otherwise.
| MangoToupe wrote:
| True. There may be australians interested in other otherwise-
| obscure islands
| LeifCarrotson wrote:
| 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?
| Majromax wrote:
| > 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.
| MadnessASAP wrote:
| 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.
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