©2019 L A Waygood
Why is the earth’s ‘Magnetic North‘ called ‘Magnetic North’, when it’s actually a south magnetic pole?
This often comes as a surprise to many people!
Some writers have put this down to a ‘mix-up’ when the poles were first named. But this is wrong! There never was any mix-up! When explained properly, it is entirely logical why Magnetic North should be a south magnetic pole.
Other writers suggest that the earth’s poles were named after the poles of a magnet —in other words, a magnet’s poles were named first. This is nonsensical because, of course, the poles of a magnet were named according to the direction in which they would point when freely suspended —which is roughly towards the earth’s ‘True North’ and ‘True South’— which has made magnets, in the form of compass needles, so useful for navigational purposes. The earth’s poles were named before those of a magnet!
Some writers even suggest that the ‘North-seeking’ end of a compass needle is actually a south pole, which is completely incorrect!!!
So why does there appear to be so much confusion on this topic? Basically, it can be put down to writers (and sadly, in some cases, teachers!) who make the subject unecessarily confusing.
The confusion exits primarily because many believe that the term, ‘Magnetic North’, refers to magnetic polarity. Nothing could be further from the truth!
‘Magnetic North‘ is simply the name we give to a location on the earth’s surface; it’s not the magnetic polarity at that location. The name, ‘Magnetic North’, is used simply in order to distinguish that location from the location of ‘True North‘. It has nothing whatsoever to do with the magnetic polarity at that location!
‘Magnetic North’ is a location, NOT a polarity!
True North and True South are fixed points located at opposite ends of the earth’s rotational axis. True North is located in the Arctic, and True South is located in the Antarctic. Magnetic North and Magnetic South, on the other hand, are not fixed points; they are relatively close to True North and to True South, but are mobile; i.e. they ‘wander’ about in the region of the True poles in rather the same way in which a top wobbles as it slows down. In the past, it has been difficult to predict precisely where it will be at any given time, because it hasn’t always followed a predicable pattern of movement! Currently, however, it appears to be moving in a relatively straight line, at a velocity of around 55 km/yr, and is now closer to Magnetic North than it has been since records began.
The difference between the locations of True and Magnetic North is called the ‘magnetic inclination‘ and this, of course, has varied over time due to Magnetic North’s ‘wanderings’. Magnetic inclination is important to navigators who rely on compasses, because it has to be figured into their calculations and, of course, it has to be regularly updated by scientists who study this topic.
Unlike True North and True South, Magnetic North and Magnetic South are not exactly opposite other! If we were to draw a line through the centre of the earth between Magnetic North and Magnetic South, unlike the rotational axis, that line would be slightly ‘bent’!
So the distance between Magnetic South and True South is not the same as the distance between Magnetic North and True North.
Magnetic North and Magnetic South describe the locations on the earth’s surface where the intensity of the earth’s magnetic flux (i.e. its flux density, expressed in teslas) is highest. Lines of magnetic flux emanate from the earth at the location of Magnetic South, and re-enter the earth at the location of Magnetic North. By common agreement, the direction of these lines of flux are from Magnetic South to Magnetic North, in accordance with the direction a compass needle would point within the earth’s magnetic field.
Although the earth’s magnetic field is often described ‘as though there was a large bar magnet within the earth…’, it’s actually results from circulating electric currents within the molten metal which exists between the earth outer and inner solid cores, some 3000 km below the earth’s surface.
The ends of a freely-suspended bar magnet come to rest pointing roughly in a North/South direction. The end of the magnet which points North was originally termed its ‘North-seeking pole’, and its opposite end, its ‘South-seeking pole’. Over time, we have dropped the ‘seeking’ part and, now, they are simply called the magnet’s ‘north’ and ‘south’ poles.
So, the poles of a magnet are named after the directions in which they point.
The poles of a compass are named in exactly the same way.
Since ‘unlike poles attract‘, the north pole of a bar magnet or compass must be attracted by a south pole, which means that the polarity of ‘Magnetic North‘ must be south.