Magnetic Storm (18 of 22)

Magnetic Storm

Now the magnetic field is outward in the northern hemisphere and inward in the southern hemisphere.
So now the burning question is, "Is what's happening in Gary's model reflected in the real Earth?"
Is the 300-year decline in our field which the pottery reveals, the work of magnetic anomalies brewing deep in the core beneath our feet?
If so, then a reversal really could be in the cards.
Amazingly, there are detailed records that cover exactly this 300 year period: the log books of Her Majesty's Navy.
For as geophysicist Jeremy Bloxham has discovered, eighteenth and nineteenth century sailors were obsessed with the magnetic field.
Back in the days of James Cook, when he was doing his voyages of exploration, a compass was the primary means of navigation.

However, a compass needle doesn't point at true north, at the real geographical North Pole, instead it points at magnetic north.
For sailors, knowing the difference between true north and magnetic north was a matter of life and death.
But as they were well aware, magnetic north keeps moving, wandering about near the pole as the field gradually changes.
So navigators needed to measure the difference between magnetic north and true north, the angle of variation.
They did this by comparing their compass bearing to an astronomical calculation of true north.
The trick was to find true north, and they could do this by looking at the sun at noon, when it's highest in the sky, alternatively by measuring the angle the sun made at sunrise or sunset.
Here, on the 8th of June, 1770, we have a magnetic variation of 4 degrees, 53 minutes east.
Thousands of these observations, together with early measures of the local strength of the field, have enabled Jeremy to reconstruct the ebb and flow of the Earth's magnetism over the past three centuries.
And it's what this reveals about one region in particular that's significant.
We've seen very abrupt changes in the Earth's magnetic field beneath the South Atlantic Ocean.