For the first time in more than three centuries, your compass might finally be about to point true north.
At some point over the next two weeks, compasses at Greenwich will point true north for the first time in about 360 years, while other parts of the UK may have to wait another two decades.
Either way, it will be a once-in-a-lifetime event.
Wait, my compass has been wrong all this time?
Afraid so – to an extent, at least.
The angle a compass needle makes between true north and magnetic north is called declination, and this changes along with the magnetic field.
Over the past few hundred years in the UK, declination has been negative, meaning that all compass needles have actually pointed west of true north.
Remind me of the difference between true and magnetic north?
Magnetic north is the direction in which the north end of a compass needle will point because of how the magnetic field of the Earth works.
The reason it is not a match for true north the vast majority of the time is that the Earth’s magnetic poles are not fixed in relation to its axis.
So why is it going to be correct all of a sudden?
Experts say the line of zero declination is moving westward at a rate of around 12 miles (20km) per year.
That means that come next month, the compass needle will point directly to true north at Greenwich, east London, before slowly turning eastwards.
How significant is this?
Well, 360 years is a very long time. For The Royal Observatory Greenwich, which was established in 1676, it marks the first time that compasses there will point true north.
Everyone else may have to wait a little longer.
Dr Ciaran Beggan, a geomagnetism scientist at the British Geological Survey’s Lyell Centre in Edinburgh, said the line of zero declination “will continue to pass across the UK over the next 15 to 20 years”.
By 2040, all compasses will probably point eastwards of true north.
Is my GPS in trouble?
You will be relieved to hear that there will be no disturbance to daily life.
Compasses and GPS will continue to work as normal.