Your compass is about to be right for the first time in 360 years

MANY of us believe we need only open a compass to find true north.

But in fact those needles have been a little wide of the mark – until now.

For the first time in around 360 years, magnetic north and true north have lined up at Greenwich. This is known because Britain has the longest series of magnetic field observations in the world, many recorded in Greenwich in the 19th century.

True north is the north you can find by following the Pole Star at night or the sun during the day. Magnetic north, picked up on a basic compass, is measured based on the movement of molten iron in the Earth’s core.

Compasses are so popular because picking one up is much easier than trying to plot a direction by following the sun and adjusting for the hour of day and where it is in the sky.

But although many people do not know it, they are often well off true north – as far as 24 degrees west of it in Britain in the 1820s, according to the British Geological Survey.

It is the BGS which has announced that true north and magnetic north are now one at Greenwich, for the first time since around 1660. The angle between them will remain small for the UK for the next few years, making life a lot easier for hillwalkers and ship’s captains.

Until now, walkers using a basic compass needed to check a map to see how many degrees magnetic north was off true north, then turn the device that many degrees before setting off.

With just one measurement now needed for north at the Royal Observatory in Greenwich, it finds itself on the ‘agonic line’ of places in the world where magnetic and true north match. Dr Ciaran Beggan, a geomagnetism scientist at the British Geological Survey’s Lyell Centre in Edinburgh, said: ‘At some point in September, the agonic will meet zero longitude at Greenwich.

‘This marks the first time since the observatory’s creation that the geographic and geothe

‘GPS will work as usual’

magnetic co-ordinate systems have coincided at this location.

‘The agonic 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.’

When true and magnetic north last lined up at Greenwich, King Charles II was on throne. But although they have lined up again in London – and in other places across the world, including in Singapore – it will have little impact on us.

Dr Beggan said: ‘Compasses and GPS will work as usual – there’s no need for anyone to worry about any disturbance to daily life.’

For some parts of the UK, it will take 20 years before their compass points true north because of the magnetic field in the part of the Earth they live above. Although basic compasses point magnetic north, smartphones’ compasses do offer a true north calculation.

The Royal Observatory Greenwich was established in 1676 and, from 1839, hosted the specialised magnetic observatory which has made continuous measurements from 1840 onwards.