what happens to a compass at the magnetic north pole
At some betoken in contempo weeks, a once-in-a-lifetime event happened for people at Greenwich in the United kingdom of great britain and northern ireland.
Magnetic compasses at the historic London area, known as the abode of the Prime Superlative, were said to have pointed direct at the north geographic pole for the showtime time in 360 years.
This means that, for someone at Greenwich, magnetic north (the direction in which a compass needle points) would have been in exact alignment with geographic due north.
Geographic north (also called "true north") is the direction towards the stock-still point we phone call the North Pole.
Magnetic north is the management towards the northward magnetic pole, which is a wandering point where the Earth'south magnetic field goes vertically down into the planet.
The north magnetic pole is currently virtually 400km southward of the north geographic pole, but can move to about 1,000km away.
How do the norths align?
Magnetic north and geographic northward align when the so-called "angle of declination", the difference between the two norths at a particular location, is 0°.
Declination is the angle in the horizontal aeroplane between magnetic north and geographic north. It changes with time and geographic location.
On a map of the Earth, lines forth which there is zero declination are called agonic lines. Agonic lines follow variable paths depending on time variation in the World'south magnetic field.
Currently, naught declination is occurring in some parts of Western Commonwealth of australia, and will probable move westward in coming years.
That said, it's difficult to predict exactly when an area will take zero declination. This is because the rate of change is slow and electric current models of the Globe's magnetic field but encompass 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 whatever time, based on predictions.
The ever-irresolute magnetic poles
Well-nigh compasses point towards Earth's north magnetic pole, which is commonly in a different place to the north geographic pole. The location of the magnetic poles is constantly irresolute.
Earth'due south magnetic poles be because of its magnetic field, which is produced by electric currents in the liquid part of its core. This magnetic field is defined past intensity and 2 angles, inclination and declination.
The relationship between geographic location and declination is something people using magnetic compasses have to consider. Declination is the reason a compass reading for north in 1 location is dissimilar to a reading for n in another, especially if in that location is considerable altitude between both locations.
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Bush walkers accept to exist mindful of declination. In Perth, declination is currently close to 0° but in eastern Australia it can be up to 12°. This departure tin can be significant. If a bush walker following a magnetic compass disregards the local value of declination, they may walk in the wrong direction.
The polarity of Earth'due south magnetic poles has also changed over fourth dimension and has undergone pole reversals. This was significant as we learnt more than about plate tectonics in the 1960s, because information technology linked the idea of seafloor spreading from mid-ocean ridges to magnetic pole reversals.
Geographic north
Geographic northward, possibly the more straightforward of the two, is the direction that points straight at the North Pole from whatever location on World.
When flight an aircraft from A to B, we employ directions based on geographic northward. This is considering nosotros have accurate geographic locations for places and need to follow precise routes between them, usually trying to minimise fuel employ by taking the shortest route. All GPS navigation uses geographic location.
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Geographic coordinates, latitude and longitude, are defined relative to Globe's spheroidal shape. The geographic poles are at latitudes of 90°N (North Pole) and ninety°S (S 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 north.
At the time of writing this article I used an online computer to discover that, at the Greenwich Observatory, the Globe'southward magnetic field currently has a declination just in a higher place zippo, nigh +0.011°.
The average rate of change in the area is about 0.xix° per year, which at Greenwich's latitude represents about 20km per yr. This means next twelvemonth, locations about 20km west of Greenwich will have zip declination.
It's impossible to say how long compasses at Greenwich will now point e of true due north.
Regardless, an alignment after 360 years at the home of the Prime Tiptop is undoubtedly a once-in-a-lifetime occurrence.
Source: https://theconversation.com/explainer-what-happens-when-magnetic-north-and-true-north-align-123265
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