So I read with some alarm a warning from the Scottish Mountaineering Association telling people to be careful about how they store.

Their compass is we carry a lot more magnets around than we used to, and that can get you into trouble.

It can deflect the needle of your compass, or in some cases, it can reverse the polarity altogether.

So got trusty compass.

Here.

Lots of surprising things have magnets in them.

Anything with a speaker in it has a magnet, and you can see just by waving the phone nearby the compass.

You can deflect the needle, and so if you inadvertently have a magnet in your sleeve as a fastening on your phone and your you have anywhere near your compass, get pointed in the wrong direction.

And if you store this compass for a long time next to something with a strong magnet, you had actually reversed the polarity of the compass needle.

But this should have opened the floodgates into learning a bit about the Earth's magnetic field.

As a whole, astronomers don't know a lot about magnetic fields.

It's a running joke that at a conference, if someone can't think of a question asked, they ask, Have you considered magnetic fields?

So, no, I would not count myself as an expert on magnetic fields if you're going out in the hills and you're going to rely on a compass, which is a good thing to do, because even if you have a GPS on your phone, which isn't going to be using years magnetic field, you never know when that might conk out.

So if you ever look closely a top, a logical map like the ones I've got here you see in the corner often a little diagram that says, Hey, be careful here.

What you think of is north on this map might not match what your compass is telling you.

The direction that the compass points is not necessarily almost never exactly at the true north towards the North Pole.

And so on every corner of every map you'll see a little correction that tells you how much you have to correct your bearings for this particular point on the earth.

So I can't say that myself.

I've ever been reliant on that level of detail in my navigation.

Plus, here in the UK, the deflections air fairly small.

So here you can see three degrees correction east of north.

But in some places, particularly near the magnetic north pole in the north of Canada, you could be out by 40 degrees.

And you definitely don't want to be relying on your compass without correcting it.

In that case, so there are multiple poles on the earth.

There's what we think of as the North Pole where Santa lives.

And this is this is associated with the rotation of the Earth.

The earth is spinning on its axis.

That access is actually tilted with respect, son.

But we won't worry about that.

Today.

The earth is spinning on the axis.

The axis of rotation goes up through the surface of the earth and subject to some caveats I'm not gonna talk about in this video is more or less what we call the geographic North Pole that the maps 0.2.

That's pretty much where your finger and thumb Er yeah, right right about there where the pins would go into a globe of the pins would go in the glove.

Yeah, but how would a compass needle no two points at the Geographic north or South Pole?

In fact, they don't the magnetic north pole in magnetic South Pole that our compasses point towards are actually in a different place altogether.

And in fact that place actually moves.

So to understand what's going on here, you really have to understand how the magnetic field of the earth is formed in the first place.

Unfortunately, we don't really know, at least not in the details.

It gets very complicated, but what we do know is that the structure of the interior of the Earth has at its core, just like this.

Plum does a very solid core of solid iron, and that's surrounded by a sea of liquid iron, and that makes up about half of the earth's interior.

So about 3000 kilometers in radius from the center.

And it's this molten iron core that we think is generating and keeping this magnetic field going.

Why would the fact that there's liquid metal suddenly so well, then you can have a magnetic field?

So now we enter the very complicated field of Magneto Hydro dynamics, where you're putting together equations from fluid dynamics like the knave, your Stokes equation and you're pulling together.

You know the core equations, Maxwell's equations from electromagnetism and you put them all together.

And you try to understand how the behavior of a conducting fluid in motion through a magnetic field what the effects of that would be.

So to produce the Earth's magnetic field, you need three things.

First, you need a conducting liquid.

You need that liquid to be in motion and not just chaotic motion, but fairly ordered flows.

And you get that from two processes.

First, Conviction s O.

The core of the earth is extremely hot and so much like a lava lamp.

It cycles through up and down and up and down and circulates.

But then it gets complicated because it's also rotating because the rotation of the earth and so this sets up.

It's a very complicated flow patterns.

And then the third really important ingredient you need is a seed magnetic field.

So something has to be there to start with.

And once you've got that, you have magnetic induction.

So you've got ah conducted fluid moving across these magnetic field lines in this ordered flow.

When you have a conducting fluid moving across magnetic field lines.

You generate electrical currents.

Those electrical currents, in turn, generate magnetic field lines.

And so you have the self perpetuating system.

Without the motions of the fluid across these men, any field lines that we would expect the magnetic field to just decay away in about 15,000 years.

So but we know it's been there for many, many geological time scales.

You can think of the magnetic field of the Earth in a very simple approximation, like a giant bar magnet, and we call that a DI polls.

It's got the north and the South magnetic poles, and then you've got these magnetic field lines that come out and around and connect them.

And so that's the simple approximation.

And if you drill line through that, you get to what we call the geo magnetic north and South Pole, which exactly opposite each other.

The geo magnetic North pole is located slightly off the coast of Greenland, and that's where you see all of the Aurora and Northern lights centered on that region.

But what we care about with our compass is the magnetic north pole, and that has a very practical definition.

That's the point on the earth's surface, where if you're carrying a compass and if you allow that compass needles to tilt in all directions, you stood over the magnetic north pole.

The compass needle would point straight down, and that's what we call North.

So when I'm literally walking around England, my needles not like perfectly flat, it's actually always tilting slightly down.

It's always tilting slightly down, and it's not necessarily pointing straight to the magnetic North Pole.

It's following whatever the local magnetic field lines are, which are actually quite complicated.

So I got this map here, which shows you the world magnetic field model.

This is essentially how much you have to correct your compass bearing by, depending on where you are on the surface of the earth.

So if you're anywhere near the green line, you're doing okay, and that's where we are.

Up here, we only have a deflection called the declination of a few degrees.

Elsewhere.

You can get up to 10 2030 degrees, and that it's not necessarily in a nice north and south pattern.

In line with lines of longitude, it gets really messy and even more interesting, the magnetic North Pole is not directly opposite the magnetic South Pole, either.

It gets really, really weird on different parts the earth, so I can show you a map of what's called the magnetic anomaly.

You can no one interesting place, which is in here.

This is the Central African Republic, a place called Bungie.

It's the site of the Bungie magnetic anomaly, and it's a place where you have no luck with your compass.

It would just be pointing all over the place because the magnetic the local magnetic field they're just goes weird is that in terms of like, there's a bunch of mountains with metal in a or the actual fundamental core created magnetic field is going weird on us.

We don't know these that cause of the anomaly.

It's probably some combination of crust and mantle interaction.

Either an igneous extrusion material from the mantel has come up and solidified or perhaps an impact from a meteorite has has done something to the crust.

But something there locally makes the magnetic field a bit wonky.

Do we know why the way that the magnetic poles turned out is so non aligned with the geographic poles, it would seem intuitive that the spinning liquid and everything that's going on would kind of roughly line up with the rotation of the Earth.

Yeah, and it it does.

I mean, when you think about it, they are pretty close to.

The North and South were only talking 10 degrees apart.

And in fact, that's predictable by what we know about fluid dynamics.

Is that the fluid in a rotating system well set up sort of these columns lined with the spin axis.

But what gets really interesting is to know that the magnetic North Pole isn't even stable.

In fact, it moves around.

We've known it moves around for quite a long time, but it's moving faster these days.

It's accelerating.

So it used to be that the magnetic North Pole was somewhere in the north of Canada, in the territory that we now call the Nunavut territory.

But it's been racing and accelerating and is now heading at great speed towards Siberia.

Interestingly, while the magnetic self pool stays more or less where it is, so that's another illustration that there's some local effect in the fluid flow underneath the North Pole, something akin to the jet stream that we see in the atmosphere that's actually driving the change in the magnetic north pole and they can't move around.

So for the past 400 years we think it was contained more or less within northern Canada.

But in the past 50 years it started to move around.

So it was moving around about tens of kilometres a year back and forth and in the last 50 years it started moving northwards and the past 30 years it's accelerated on this year.

It's now moving at 50 kilometers over the course of the year heading towards Siberia.

But they put a stake in the ground or anything like they do at the South Pole is that is this position marked and anyway and just have to move the marker.

It's marked on maps, but it's not gonna be a physical marker, partly because of how fast it's moving and partly because the nature of where it is there's no there's no solid ground up there or solid ice that's reliable, particularly since the Arctic ice is now melting at an accelerating rate.

Eso no, nobody's up there moving markers around, but because of this motion, normally the magnetic maps are updated every five years, and they've actually had to do an inter cycle sort of emergency update to that because it's moving so fast.

It's not gonna affect anybody here using their compass to walk in the, you know, with the Highlands of Scotland.

But it is gonna make a difference for anybody relying on the fine details, particularly up in the north northern latitudes.

I don't know anyone who is more proudly Canadian than you.

How do you feel about Canada potentially losing the magnetic North Pole?

Well, I only actually learned that fact today, and I do feel a bit sad because I was a source of national pride that for hundreds of years we have been magnetic North Pole within our territory.

But there's nothing I can do about it.

I can't hang on to it.

So this is the neat thing.

The magnetic North Pole might be moving around and taking a bit of an excursion around northern latitudes.

But we also know that quite regularly on geological time scales, the whole system flips.

So just like I was talking about my compass, reversing its polarity, the whole magnetic field of the earth occasionally slips so that the North Pole becomes south from the South Pole becomes the north.

We don't know why this is again in the details because it's an immensely complicated scenario, but we do know that it happens and it happens with great regularity, if not period ISS ity.

So we know that there have been 183 reversals in the past 83 million years.

Andi.

That's a record that we can establish really well, thanks to geological measurements of the magnetic field.

Because we have this really interesting phenomenon that when molten mantle material comes out and solidifies that cooling volcanic rock retains sort of the fingerprints of the Earth's magnetic field direction at that time.

So we go back to our magnetic anomaly map.

You actually see here in the mid Atlantic or the mid Pacific, that where material is coming up from the crust and where these tectonic plates are being pushed apart.

You've got this regular incursion of liquid mansell coming up and solidifying its retaining the direction of the magnetic field of the earth as it swaps back and forth.

So, on that map, we've got these stripes of red and Blue, which indicate that the field's been switching back and forth.

What does a flip look?

Look again?

We don't really know.

So we can do models, and we can do some quite interesting models.

Here's computer models of what a flip might look like done in a soup and computer.

So here's what we think the magnetic field of the Earth might look like now.

And so you've got these nice, well defined die pole magnetic field lines coming out, but a big mess locally towards the surface of the earth.

Some point through a reversal, you might get a situation like this where it's just a big mess.

You might have the North and South Pole just wandering around.

They might disappear.

You might have more than one poll pop up chaotically in different places.

The magnetic field of the whole earth might decrease altogether.

We don't really know Best estimate, so that it might take 1000 or tens of thousands of years toe happen.

Um, some people think it might happen within a human lifetime.

Does that mean we could see what happened?

Well, it's an interesting thing to think about that we have seen the magnetic North pole.

Go for a wander.

That wondering seems to be accelerating since we've been met making measurements since by 18 40 there's been a steady decrease in the strength of the magnetic field, So it's leading some people to think that we might be in the early stages of a reversal.

But whether that happens next year or in the next 10,000 years, we can't be so sure.

Sometimes the magnetic field just goes on a bit of a wobble cold excursion, but then it comes back to the normal polarity.

But when it does flit from one end to the other, we mark those geological time scales in periods called Cron's.