North Pole Wanderings

A daily log entry

I live on a boat and at the top of every page of my ship’s logbook is a line which says: Compass variation …

Today, as I write — in Indonesia (we got there) — compass variation is 2⁰ East. Last year, when I was in New Zealand, it was 18⁰ East. That’s a big difference between True North (where Polaris, the Pole Star sits if you are in the northern hemisphere) and where my compass needle points, Magnetic North.

The difference between True North and Magnetic North varies slowly with time as the Magnetic North Pole meanders (it’s in the Arctic), and with location on the earth’s surface — which can change rapidly if you are flying in a plane.

The movement of Earth’s north magnetic pole across the Canadian Arctic in recent centuries, continuing in recent years across the Arctic Ocean towards Siberia.

Electronic navigation

My electronic charts have a built-in subroutine which uses data from the World Magnetic Model to give me the precise local magnetic variation.

This is what it shows today:

So what’s afoot?

The meanderings of the magnetic north pole will soon bring the variation between true north and magnetic north to zero in the United Kingdom, reportedly for the first time in history.

This is what the British Ordnance Survey says:

“The alignment will make landfall at Langton Matravers, Dorset, this month [October 2022] and reach Poole by Christmas [2022]. By August 2024, it’ll pass through Hebden Bridge and leave the English coast at Berwick-Upon-Tweed in August 2025.

In 2026, it will hit land again at Drums in Scotland around May before making a last stop in Fraserburgh in July.” — TheRegister

“These predictions are likely to change (by a few months only) with the assimilation of new magnetic field observations into the model. This new data will capture the latest magnetic field signals from the geodynamo operating in the Earth’s liquid outer core. Interactions between the flow of the molten iron-rich material in this region and the magnetic field generate electrical currents that, in turn, creates new magnetic flux which sustains the field

“Energy sources for the fluid motions are primarily convection — as the Earth slowly cools down, warmer fluid rises and cooler fluid falls and solidifies onto the solid inner core. This changes the chemical composition of the fluid making it less dense, from which buoyancy forces result. The rotation of the planet also contributes to sustaining the geodynamo.

“And that will be that, for a few hundred years at least. 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.”

For clarity, the third north is ‘grid north’ as shown on Ordnance Survey terrestrial maps.

Video from the British Ordnance Survey:

Importance

These days with GPS navigation the magnetic variation is little more than a curiosity to many sailors.

My boat is steel and there are other magnetic effects (deviation) on my compass which total, with magnetic variation, to a number called Compass Error. The maths is fiendishly complicated as the deviation is affected by the roll, pitch and yaw of a vessel. It’s way beyond the scope of this story and my brain, but if you want to know more then check out deadreckonings.com.

For newbie sailors it can be a bit daunting to deal with, especially when the variation and deviation are named in opposite directions.

Fortunately that’s not too much of a problem on a small boat like mine and my deviation (!) is less than 10⁰ on any heading (it varies with the boat’s angle relative to the earth’s magnetic field). It an change with time and also after I’ve been doing a bit of welding. So, deviation has to be checked regularly — it’s called swinging the compass.

So, I take note of the deviation, variation and total error. I never know when I might need to use them seriously.

What happens when Putin pushes a button and we lose our GPS signals?

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Canonical: This story was first published in Medium on 8 November 2022