Compasses to Point True North for First Time in 360 Years

At some point over the next two weeks, compasses at Greenwich will point true north for the first time in about 360 years. And for some parts of the UK, this may not happen for another 20 years. Either way, it is a once-in-a-lifetime event.

The angle a compass needle makes between true north and magnetic north is called declination. As the magnetic field changes all the time, so does declination at any given location. Over the past few hundred years in the UK, declination has been negative, meaning that all compass needles have pointed west of true north.

The line of zero declination, called the agonic, is moving westward at a rate of around 20km a year, experts say. By next month, the compass needle will point directly to true north at Greenwich in London, before slowly turning eastwards.

The Royal Observatory Greenwich was established in 1676 and, from 1839, hosted the specialised magnetic observatory that made continuous measurements from 1840 onwards. In 1926, the instruments were moved to Abinger in Surrey, as electrified railway lines had made it impossible to measure the magnetic field.

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https://www.theguardian.com/science/2019/aug/30/compasses-to-point-true-north-for-first-time-in-360-years

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