Does a Compass Read True North or Magnetic North
At some indicate in recent weeks, a one time-in-a-lifetime upshot happened for people at Greenwich in the United Kingdom.
Magnetic compasses at the historic London expanse, known equally the home of the Prime Height, were said to have pointed directly at the north geographic pole for the outset time in 360 years.
This ways that, for someone at Greenwich, magnetic north (the direction in which a compass needle points) would have been in exact alignment with geographic north.
Geographic north (also called "true north") is the direction towards the fixed betoken we call the N Pole.
Magnetic north is the direction towards the north magnetic pole, which is a wandering betoken where the Earth's magnetic field goes vertically down into the planet.
The north magnetic pole is currently about 400km south of the n geographic pole, but can motion to about 1,000km away.
How do the norths marshal?
Magnetic due north and geographic due north align when the so-called "angle of declination", the difference between the 2 norths at a particular location, is 0°.
Declination is the angle in the horizontal airplane between magnetic n and geographic n. Information technology changes with fourth dimension and geographic location.
On a map of the Earth, lines along which there is cypher declination are called agonic lines. Agonic lines follow variable paths depending on time variation in the Earth's magnetic field.
Currently, zip declination is occurring in some parts of Western Australia, and will likely move westward in coming years.
That said, it's hard to predict exactly when an surface area will have null declination. This is considering the rate of change is dull and current models of the Earth'southward magnetic field only cover a few years, and are updated at roughly five-year intervals.
At some locations, alignment between magnetic north and geographic north is very unlikely at any time, based on predictions.
The ever-changing magnetic poles
About compasses betoken towards World'south n magnetic pole, which is usually in a unlike place to the north geographic pole. The location of the magnetic poles is constantly changing.
Earth's magnetic poles exist because of its magnetic field, which is produced by electrical currents in the liquid part of its core. This magnetic field is defined by intensity and two angles, inclination and declination.
The relationship betwixt geographic location and declination is something people using magnetic compasses have to consider. Declination is the reason a compass reading for north in i location is different to a reading for northward in another, especially if there is considerable distance between both locations.
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Bush-league walkers accept to be mindful of declination. In Perth, declination is currently shut to 0° just in eastern Australia it tin can exist up to 12°. This difference can be pregnant. If a bush walker post-obit a magnetic compass disregards the local value of declination, they may walk in the incorrect direction.
The polarity of Earth'southward magnetic poles has also changed over time and has undergone pole reversals. This was meaning as nosotros learnt more virtually plate tectonics in the 1960s, because it linked the idea of seafloor spreading from mid-ocean ridges to magnetic pole reversals.
Geographic north
Geographic north, possibly the more straightforward of the 2, is the direction that points straight at the North Pole from any location on Earth.
When flight an aircraft from A to B, we use directions based on geographic n. This is considering we have accurate geographic locations for places and need to follow precise routes between them, usually trying to minimise fuel use by taking the shortest road. All GPS navigation uses geographic location.
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Geographic coordinates, latitude and longitude, are defined relative to World'due south spheroidal shape. The geographic poles are at latitudes of 90°N (North Pole) and xc°S (Due south Pole), whereas the Equator is at 0°.
An alignment at Greenwich
For hundreds of years, declination at Greenwich was negative, meaning compass needles were pointing west of true northward.
At the fourth dimension of writing this article I used an online computer to detect that, at the Greenwich Observatory, the Earth's magnetic field currently has a declination just higher up zero, well-nigh +0.011°.
The average rate of alter in the area is about 0.19° per year, which at Greenwich's latitude represents about 20km per year. This means adjacent yr, locations about 20km due west of Greenwich will accept zero declination.
It's incommunicable to say how long compasses at Greenwich will now betoken east of true north.
Regardless, an alignment subsequently 360 years at the habitation of the Prime number Meridian is undoubtedly a in one case-in-a-lifetime occurrence.
Source: https://theconversation.com/explainer-what-happens-when-magnetic-north-and-true-north-align-123265
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