Three norths collide!

 

Here's an interesting quirk from the Ordnance Survey: for the first time ever the three types of north they identify on their maps will coincide - they will all be pointing in the same direction. But only at a certain place and at a certain time! True north means the direction you go to head directly to the geographic north pole - the axis of the Earth's rotation. Because the Earth is curved, these lines get closer together the further north you go. Try drawing lines going from the stalk of an apple to the bottom - they start close but spread apart round the middle of the apple and then come back together again. Now look at a map: all north pointing grid lines are parallel and do not get closer as you head further north. This is an approximation to make curved space sit on a flat paper. It is arranged so that one special grid line is actually true north. Then there is magnetic north. The magnetic pole of the Earth wanders and in the next year or two, there will be times when if you stand on that special true north grid line, your compass will also point along that line. Three norths collide!! It's well explained in this film.