Magnetic declination - Earth's magnetism

suppose you're tired of all the digital world and all the apps and technology and you decide to walk or swim towards the arctic ocean in the north pole without any gadgets and find peace over there i have one question for you how would you reach there without any gadget well you say ha all i need is a compass compass will tell me where the north pole is but even if you had an awesome compass and you followed it exactly you will not reach the north pole at all you completely miss it why well let's find out so to solve this mystery let's first start by asking ourselves some fundamental questions about the earth first of all what do we even mean by the poles of the earth well we know the earth spins around its own axis and so wherever this axis touches the surface of the earth those are what we call the poles so there are two points one near the arctic ocean is called the south pole sorry north pole and the one in antarctica is called the south pole okay but what's this got to do with your compass why does the magnetic needle always align along the north and south well that's because and this is something you may have already learned earlier that's because earth itself behaves like a giant magnet you may have seen pictures which show the magnetic field lines of earth now we're not exactly sure how the earth is able to generate the magnetic field what causes it there are theories out there but we don't have a conclusive answer yet but the for the purposes of this video let's just assume that there is a giant bar magnet inside the earth okay although there isn't it just makes our you know our life much easier so here's a question for you now we now know that the north pole of our needle gets attracted to the north of our earth right and we're now imagining that there is a bar magnet inside the earth so my question to you is which pole of that bar magnet is in the north pole of the earth is it the south pole of the bar magnet or the north pole of the power magnet can you pause and think about this for a while all right well we know that north is always attracted towards the south and since the north is pointing towards the north pole there must be the south pole of the bar magnet over there and therefore if you visualize the bar magnet it's kind of reversed does that make sense because the needle is because the not pull of needle is attracted to the north pole that means the south pole of the magnet should be at the north pole long story short earth's north pole kind of behaves like a south pole of a giant bar magnet inside of it okay so if we digest all of this this means we can use our compass and to help us find where the north pole of our earth is so now we come back to the original question i said that if you were to just walk with your compass you will not end up at the north pole why did i say that well that's because there's a small small thing that i have i haven't mentioned over here it turns out that the axis of the bar magnet does not exactly align with the earth poles earth's pole in fact it's tilted a little bit like this this means the south pole of that giant hypothetical bar magnet inside the earth is not exactly in the arctic ocean it's not exactly over here but it is somewhere shifted and i googled it it turns out about 400 kilometers shifted somewhere in northern canada and so now you can see the problem let's say this is you who wants to swim to the arctic ocean then this is the path that you want to take towards the north pole towards the artic ocean but if you follow your compass it will not lead you over there it will lead you somewhere over here you will end up taking this path and you will miss the north pole and so this this place where you would reach now this place is called the earth's magnetic north pole this is called the earth's magnetic north and the actual north the north what we mean is often called the geographic north or some people often say true north you can also call this true north now you might feel a little uncomfortable and i do as well in calling this magnetic north because really it's a magnetic south and so there is a confusion there's a lot of confusion out there some people say hey if we call this as the magnetic south pole then the magnetic south will be close to the true north and that's going to be confusing but some people say hey if you call this magnetic north but you know the field lines are entering over there so it should really be the south pole so you know what let's not worry too much about this nobody's going to question you what is it really called all that matters is this behaves like the south pole of a giant bar magnet okay that's all that matters okay so don't don't worry too much about the confusion anyways let's come back to our point you need to swim to the arctic ocean right how do we how do we make sure that you end up over there well all you need is the correction factor if you can get this angle between the true north the path to the true north and the path to the magnetic north if you can get that angle then you are done you can course correct yourself if this angle was say for example 2 degrees to the east and if you knew that right then what you would do ideally is you would look at the compass and you would say okay i don't want to move this way i need to move two degrees east of this and then you would be on the right path okay so this angle is super important for navigation and we give a name to that angle we call that magnetic declination i know it's a little crowded so let me write over here it's called magnetic declination okay we are not done yet so before we continue let's let's uh you know check your understanding uh do you think the value of magnetic declination would be the same at everywhere on the planet or do you think it will change from place to place why don't you pause the video and think a little bit about this okay all i have to do is pick another point and see what would my compass what path would my compass lead to and what path i would really need to go and to make things easier what i'll do is i'll consider a path i'll consider a point somewhere over here now if you had to use a compass well you will end up going this way this is the path but where do you really want to go if you want to go to the north pole this is the path that you need to take and so now this would be the new angle i don't know you can see that hopefully and you can immediately see that angle is different than this angle in fact that angle is larger than this angle because you're already a lot off course over here and so clearly you can see that the value of magnetic declination keeps changing and it has different values at different places which means it's not like you can look at you know at one place and you can say ah i know the magnetic declination value now i'm on the right track no no you pretty soon go off track if you just use that value everywhere so you have to constantly keep updating yourself constantly keep looking what the new magnet declination is at every point and constantly keep course correcting yourself so a quick question you might have is how do we record the declination values everywhere on the planet like do we like how do we write it like you know how do we communicate that how do i use it how do i read that okay so this is where graphs are super important so there are graphs drawn will not get into too much detail you can do the research but you know let me quickly show you what it would look like so here's the world map and all these lines represent a particular declination value for example if you are somewhere over here then you are on this green line and the green line represents 0 meaning it says at this point the declination is 0. and then you walk somewhere and maybe you are now somewhere over here now you are on this blue line and notice this blue line says declination value is negative 10. they have some notation maybe i think towards the east is called negative towards the west is called positive or something like that but so if you look at this map anywhere you are on the world you can figure out what the declination value is by looking at which line you are on all right again let's not worry too much about that so there are ways in which you can figure you know these maps help us know what our declination values are all right the last thing i want to do before winding up the video is some formalities for your exam how do you define the magnetic declination angle right now so far we said this path the angle between this path and this path is the magnetic declination and that's fine for me but for in physics we need to have very precise you know definition so how would you put this in words can you pause the video based on whatever just learned you can think about how would we put this in words all right maybe you would say something like okay it's the angle between the line joining the you know your point where you are at or the point on the earth and the true geographic north and the line joining the point on the earth and the magnetic north right looks fine and again i would give full marks for that but there's a problem the word line you know is causing problem because you know in physics or in math line means a straight line and when you're drawing a line on earth it's curve so you can't usually you can't just say a line the second problem is you know i can draw multiple lines from here to the true geographic node i can draw some random line like this right so how do you represent this line the line along the longitude okay maybe you might say something like okay maybe the shortest line between this you know what let's stop i'll just tell you i'll just tell you how we define it instead of calling this a line that's the only problem we have instead of calling this a line if you were to complete that path go all the way around the world what shape would you end up with well you can kind of visualize you will end up with a circle and although it doesn't look like a circle hopefully if i slice the earth along that path you can kind of see this is a circle it's look you know a circle looked at from from a cider okay so we could say it's the angle between this circle and how do we define this circle we could say it's a circle that passes through the point on the earth and the earth's you know true north and true south poles or you can say it has the the mac the the earth's axis as the diameter okay so this is one circle we can use to define and similarly we can have another circle for that you walk along this path what your compass shows and again complete that entire journey and now you would get another circle again this is a circle okay if i were to slice the earth now you know you slice it this way this is what it looked like that in the another circle and how do you define this circle well we could say this is the circle that passes through the point where you are standing or the point on the earth where we are calculating the declination values and the earth's magnetic north and there will be a magnetic south somewhere down there magnetic northern magnetic south poles or you could say it's the it's the circle that passes through this point on the earth and the earth's magnetic axis you can call this as the magnetic axis and we could now say declination is the angle between these two big circles and because these circles are so useful in definition we give names to these circles this circle is called the geographic meridian both circles such circles are called meridians by the way so these are called this is called geographic meridian and this circle the other circle because it's along the magnetic sorry let's use light color because it's along the magnetic we call this light color light color okay we call this the magnetic uh meridian magnetic meridian okay fancy names are being used but you get the idea right what these two are and so what's magnetic declination now we could say magnetic declination is the angle between the geographic meridian and the magnetic meridian and if anybody asks what exactly is a geographic meridian it's this for geographic medium you can just imagine the longitude circle at a particular point and the magnetic meridian is something very similar but this circle has the earth's magnetic axis as the diameter okay passes through the earth's magnetic axis so to quickly summarize we saw that if you just use your compass it doesn't show the true north pole and so there is a correction factor required if you want to navigate properly and that angle is called magnetic declination the value of the declination changes from place to place and also from time to time actually again let's not worry too much about that and how do you define the magnetic declination we say the is the angle between or the acute angle because there are two angles actually the acute angle between the geographic and the magnetic meridian and finally what exactly are these meridians well geographic meridian is a circle it's basically the longitude circle it's a circle that has the you know it passes through the geographic north and south poles and if you just say that you can draw many circles right and the point at which you're calculating the magnetic declination similarly what's the magnetic meridian it's a circle that passes through the earth's magnetic north and south poles and and the point at which you're calculating the magnetic declination so the angle between them is the magnetic declination