Interesting press release from the British Geological Society:
Hold onto your compass: true north and magnetic north cross at Greenwich for first time in 360 years.
Compasses at Greenwich will point to true north for the first time in 360 years at some point within the next two weeks.
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. For 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 present rate of around 20 km per year. By September 2019, for the first time since around 1660, the compass needle will point directly to true north at Greenwich, London, before slowly turning eastwards.
We live on a wonderfully dynamic and fluid planet. All sorts of things are in continuous flux - the magnetic poles, solar output, variable climate, sea level, composition of our atmosphere.
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