Magnetic north, true north and grid north align over UK
Discussion
"The difference between magnetic north and grid north is often referred to as ‘grid magnetic angle’ and it not only varies from place to place, but changes with time. This needs to be taken into account when navigating with a map and compass.
In 2014, for the first time in Great Britain since the 1660s, magnetic north moved from being to the west of grid north to the east. The change started in the very south-west corner of Britain and will slowly progress across the whole country over the next 12 to 13 years.
Now, there is a third line about to come into alignment – true north. This is the direction of lines of longitude that all converge at the north pole. "
https://www.ordnancesurvey.co.uk/newsroom/blog/mag...
In 2014, for the first time in Great Britain since the 1660s, magnetic north moved from being to the west of grid north to the east. The change started in the very south-west corner of Britain and will slowly progress across the whole country over the next 12 to 13 years.
Now, there is a third line about to come into alignment – true north. This is the direction of lines of longitude that all converge at the north pole. "
https://www.ordnancesurvey.co.uk/newsroom/blog/mag...
Beati Dogu said:
This needs to be taken into account when navigating with a map and compass.
In 2014, for the first time in Great Britain since the 1660s, magnetic north moved from being to the west of grid north to the east. The change started in the very south-west corner of Britain and will slowly progress across the whole country over the next 12 to 13 years.
Interesting, as I haven't used a map and compass for years.In 2014, for the first time in Great Britain since the 1660s, magnetic north moved from being to the west of grid north to the east. The change started in the very south-west corner of Britain and will slowly progress across the whole country over the next 12 to 13 years.
Does this mean that the old phrase for remembering which way to convert map to compass and vice versa of:
"Grid to mag - add
Mag to grid - get rid"
Is now completely wrong (in south-westerly regions of Britain, and increasingly the rest of the country as time passes)?
C n C said:
Interesting, as I haven't used a map and compass for years.
Does this mean that the old phrase for remembering which way to convert map to compass and vice versa of:
"Grid to mag - add
Mag to grid - get rid"
Is now completely wrong (in south-westerly regions of Britain, and increasingly the rest of the country as time passes)?
Depends where you are. Each os map tells you what it was at printing and the yearly adjustment. Does this mean that the old phrase for remembering which way to convert map to compass and vice versa of:
"Grid to mag - add
Mag to grid - get rid"
Is now completely wrong (in south-westerly regions of Britain, and increasingly the rest of the country as time passes)?
ks off you (even more) to save the planetIIRC since that point is not "at" the true North pole it's apparent location to East or West will depend where you're looking from.
What I've not understood is the difference between grid North and true North. Unless the grid is based on a projection and doesn't really point at anything.
What I've not understood is the difference between grid North and true North. Unless the grid is based on a projection and doesn't really point at anything.
I read this and am still no wiser as to what 'aligns over the UK' means: https://gisgeography.com/magnetic-north-vs-geograp...
Panamax said:
IIRC since that point is not "at" the true North pole it's apparent location to East or West will depend where you're looking from.
What I've not understood is the difference between grid North and true North. Unless the grid is based on a projection and doesn't really point at anything.
Basically yes. The grid is parallel lines and only really works for a small area (eg the uk). Whereas lines of longitude (which always point to true north) converge as they go to the poles.What I've not understood is the difference between grid North and true North. Unless the grid is based on a projection and doesn't really point at anything.
From the OS website:
"Across OS maps true north varies from grid north since it reflects the curve of the earth, except on one grid north line, which aligns with longitude 2 degrees west of the zero Greenwich meridian line. Anywhere on this ‘special line’ grid north and true north align."
Simpo Two said:
Mave said:
Simpo Two said:
Surely that's true for the rest of the world too...
I don't think so - some of the world its west, some is east. Do you mean its position varies depending on whereabouts on the planet you measure it from?
Let's say Magnetic North were in London. If you're on the equator at 0E then there's no deviation. As you travel East, magnetic North starts appearing West of true North. If you travelled West, then magnetic North would start to appear East of true North.
Unless magnetic North is actually at the pole, then there are only two lines of longitude which have zero variation - the one which the magnetic pole is on, and the one 180 degrees away on the other side of the globe.
So the magnetic pole has now shifted to align with our line of longitude, which means that for everyone West or East of us, it isn't aligned.
Edited by Mave on Thursday 10th November 20:07
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