Outdoor fans can probably ignore magnetic variation for a while. Photo: Bob Smith/grough
A unique triple alignment of one of the cardinal points of the compass will occur this week.
Britain’s national mapping agency Ordnance Survey said all three norths – grid, magnetic and true – will combine at a single point in southern England for the first time.
The phenomenon will then slowly move northwards in Britain over the next few years.
Langton Matravers, a village west of Swanage in Dorset, is where the alignment will happen first.
People navigating with a map and compass have, for years, been aware of the need to account for magnetic variation – the difference between grid north and magnetic north – for accurate travel.
Grid north is the alignment of Ordnance Survey’s grid covering Great Britain: the blue lines marked at 1km intervals on 1:25,000 and 1:50,000 maps. Magnetic north is the direction your compass needle points to, and is dependent on the movement of molten iron in the earth’s core.
True north, which is not widely used in land navigation by outdoor enthusiasts, is the direction of longitude lines running from pole to pole.
Because the OS grid is a flat representation of the earth’s curved surface, variation of the norths differs across the country. Only one grid line, which coincides with 2 degrees west, actually points to true north.
Ordnance Survey said: “After always being to the west of grid north in Great Britain, the last few years have seen magnetic north move to the other side of grid north. The change started in 2014 at the very tip of Cornwall and is slowly moving west to east across the country. It is now reaching the ‘special line’ and will incredibly converge with the other two norths for the first time in history.
“After making landfall at Langton Matravers, the triple alignment will pass northwards through Poole by Christmas and then Chippenham and Birmingham before reaching Hebden Bridge in Yorkshire in August 2024.
“It will pass though the Pennines before leaving the English coast at Berwick-upon-Tweed a year later in August 2025 and it does not hit land again until around May 2026 at Drums, just south of Newburgh in Scotland. After passing through Mintlaw, its last stop in Scotland and the landmass of Great Britain is Fraserburgh, around July 2026.”
OS said the predictions are likely to change, but only by a few months. The British Geological Survey provides updated magnetic observations based on the changes in flow of the earth’s outer core. Its geomagnetism team makes detailed measurements at 40 sites across the UK.
Dr Susan Macmillan of the BGS said: “This is a once in a lifetime occurrence. Due to the unpredictability of the magnetic field on long timescales it’s not possible to say when the alignment of the three norths will happen again.”
Mark Greaves, earth measurement expert at Ordnance Survey, said: “It is no exaggeration to say that this is a one-off event that has never happened before. Magnetic north moves slowly so it is likely going to be several hundred years before this alignment comes around again.
“This triple alignment is an interesting quirk of our national mapping and the natural geophysical processes that drive the changing magnetic field.
“But for navigators the same rules will apply whether they are simply on a trek or a walk or flying planes or navigating ships at the other end of the spectrum. They will always have to take account of the variation between magnetic north from a compass and grid (or true) north on a map.”
OS paper maps have the predicted magnetic variation marked on their margins to help navigation, but for outdoor enthusiasts in many parts of Britain, this will be so small as to obviate the need to calculate the declination over the next few years. General purpose compasses on sale to walkers are usually accurate to one degree.
An OS video explains the three norths
Jock
02 November 2022Far more interesting than falling from Striding Edge.
Cameron
03 November 2022I guess this is going to impact all our lives more than we ever imagined. I'm just concerned that the mountain rescue teams will end up getting even more calls because of all the people not accounting for this navigational change.
As an aside, I heard something really interesting the other day. Apparently some scientists in one of the top research institutions have worked out that really big stones are harder to lift because of their weight.
Old Git
03 November 2022I can't sympathise with your logic. A significant number of hill-goers don't even carry a compass, let alone know how to use one, so this will probably make little difference to callout frequencies.
Doug
04 November 2022Thanks for putting it in perspective Cameron, interesting stuff. Not sure everyone gets your point
P
07 November 2022Human error with taking a bearing is a much bigger issue than people not adjusting for magnetic variation when it comes to navigation errors.
Unless you are calling in an artillery strike, for UK purposes on the hills, magnetic variation has little impact on navigation accuracy. If you are walking on a bearing, your legs should be short and even in whiteout conditions, when used with pacing, timing and contour interpretation, by not adjusting for magnetic variation will have zero impact on accuracy. You are more likely to not correctly align your compass on the map or on the ground.
Taking super long legs on a bearing is not good practice so negates the impact along with the human error factor. I haven't adjust in the UK for about a decade and it's had no impact for me even in night time, whiteout conditions...and my job is guiding and instructing on UK mountains!
Andrew W
08 November 2022#P
there's always someone who claims to know it all isn't there
James
09 November 2022Andrew - think about what 'P' is saying - if not in a warm comfortable room then taking a bearing from a map on a cold, wet and windy hillside provides a number of opportunities for minor errors to creep in during the procedure. Also, consider the opportunities for error when walking on a bearing.
Good navigation involves much more than 'just' following a compass bearing.
Mike W
09 November 2022This isn't TicToc, lets keep comments (whether in agreement or disagreement) constructive and informative. No need for sarcasm / vitriol.
#P's point is fair and relevant - this article is really interesting science (for geeks like me) but from a basic compass navigation angle there are many factors that are much more important for most hillwalkers to get right before even considering the vaguaries of magnetic variation.