while waiting on a plane during taxi till takeoff looking out the window you may have noticed the giant numbering the runway say eight which implies seven others exist at least but this is a flight out of LOL airport in Nevada's Desert of Nothing there's only two runways which given the passenger load seems like maybe one too many already what's the deal with runway numbers you might wonder aloud oh hello again flying to Nook as well are you it is a long flight so there's tons of time for me to tell you all about runways let's begin so before you can number a runway at an airport you need to build the airport and before you can build the airport you need to plan the port and what needs figuring first is which way to run the way pilots want runways with winds in parallel for physics reasons that we are going to skip both because lift physics is something people really like to argue about and this isn't a physics video yeah I'm recording a runway video right now hope you don't mind but the summary is planes take off and land into the wind because it lets them use less runway and makes for safer and stabler landings in particular now planes can land with winds unaligned but it's unsettling to watch these crosswind attempts as pilots do their best to face into the wind while landing on a runway that does not o so airports too want winds running with the runway but the universe is indifferent to human desires wind wines as it wants so the simple solution in aviation early days was to build a triangle of runways put up a little wind sock and direct the pilot to the runway that paralleled the sock and thus the wind but as aviation grew so did airplanes and thus their runways making the triangle trick impractical for big urban internationals but the simple sock still solved it see if you record when and which way the wind sock blows and with what wind force you've grown yourself a wind rose a clever little data viz tool with the sock in the center of compass points for orientation and bars colored in size for strength and frequency of wind though it reads opposite actually of everyone's expectations with the lines showing the way the wind blows from and not to physics stuff just loves to opposite actually let's just agree to avoid physics for this video shall we wind roses reverse readings aside they reveal that in most places most of the time most of the wind mostly blows back and forth in one direction so that's surprisingly convenient thanks in different universe oh you did it for other reasons well still this convenient wind happens because wind is a current of air transporting heat from where there's more to where there's less the Earth is blasted by the nuclear heat of the sun with the equator getting hit hot hardest making hot air rise there as it cools out along the edge of space before coming back down creating a big scale convection current that repeats in a pattern all up and down and because the Earth is a sphere that spins those cylindric convection currents of air on the surface twist clockwise north of the equator and counter below this is the coriololis effect creating coiled currents of air everywhere which is cool but also physics trying to sneak back into the video and this isn't a physics video all that matters is this creates the pretty stable pattern of trade winds and if you're planning a port you need only know which way does the wind mostly blow though at some locations the wind rose reveals two frequent directions of wind so if you want to constantly and safestly keep open the airport you're going to need to run a second way this is why many airports have an X or V layout like LOL they're not necessarily doing double the traffic of a one runway port but rather have double the chance of crosswinds when the tower will need to reroute pilots toward the other alignment for safer landings and once you have two of something you need names or numbers sure you could just go with run one and run two but pro tip try never to use the very first thing that comes to mind without giving it a bit of a ponder first and the wind rose reveals a better way with the compass points which form a circle of 360° starting at 0 north east 90 south 180 west 270 and back to north makes it 360 as well these compass degrees come from ships of the seas because captains and porter masters when in the vast featureless nothing could still count on their compass to point toward the north pole assuming no iron hooks happen nearby and with north as a fixed navigational point could then communicate their heading with names broadly eastsoutheast or numbers precisely helm to 108 quite handy so it's no surprise these compass headings got passed from sea ships to airship thus on the windrose devised plans for any airport the runway is already aligned with navigational numbers begging to be used but before grabbing the obvious one again ponder for a moment the runway points from the perspective of the port toward the plane the rather more important heading to use is from the plane's perspective approaching the port which on the plan is at the opposite end actually because it's what number matches the compass in the cockpit that's critical all right this needs a couple of example airports take one with a north south runway when the wind blows from the north to the south the tower directs pilots to approach from the south meaning they need to point the plane north which on their compass is a heading of 360° so let's put a big 360 on that end for now when the winds reverse the tower directs pilots to approach from the north to fly south which reads 180 so let's put a big 180 on that end as well now that we've got our heading numbers the convention is to round them to 10 and cut off the zero for the runway number because we don't need three sigfigs of precision when airports have singledigit numbers of runways and the very stressed air traffic controllers in the tower need to repeat precisely these numbers hundreds of times a day so saving syllables here really matters thus when the tower tells the plane to use runway 36 the pilot knows they need to get south of the airport to land facing north and while there are like a million indicators in a cockpit the pilot can always confirm they're doing it right by reading 360 on their ancient ancestors compass this low tech check is useful as a fallback because a compass can see the way even when eyes and other equipment cannot as a two runway example an airport with a perfect ordinal X would get numbered thusly northwest to southeast gives 315 for one end because that's the way the pilot needs to point and 135 at the other round to 10 for 320 and 140 then drop the zeros to get runways 32 and 14 on the other side 225 and 45 round to 10 again drop the zeros for 23 and five now when the towers talk to the pilots they say each digit individually so runway 23 because clarity here is critical which is also why the font and exact size of these digits is standardized worldwide though there are disagreements between the abundant aviation agencies as to if singledigit runways like six should have a leading zero for clarity or if that leading zero should only be in our hearts which it shouldn't be anyway that's the surprisingly good system behind numbering these numbers which is always a delight to discover unlike some other numbers I could mention though there are a couple of wrinkles for think about it if the wind mostly blows back and forth in most places then most big busy urban international airports will need multiple runways in parallel but parallel runways have the same heading thus the same number under this system which would be unclear for pilots to say the least so all the agencies assembled to agree if you have two parallel runways they will have the same number but add an L or an R for left and right if you need to construct a third runway add a C for center 2 but with four or more two runways will get the correct heading number with L and R but the others they're going to get the next closest numbers but not exactly correct numbers which is practical I suppose but also ah it's all slightly misaligned it's big airports like it the it doesn't line up like just try not to think about it okay just try not to think about it oh we're landing at Nook already wow flights fly fast when you're flapping about flying time to put this knowledge to use our compass heading reads 42° so round 210 440 cut the zero and we'll be landing on runway 04 and since there's only one runway at Nook it'll be perfectly aligned no doubt about that oh it's five not four how embarrassing i guess I need to delete this video now hey why are you painting a new runway number you do that every few decades that must mean Oh runway numbers depend on where the North Pole is and so watch out there's a geography video inside this video called Where is the North Pole really okay to find the North Pole remember that the Earth is a sphere that spins oh sorry we already went over that we draw a line about which this spin occurs and name each end the North and South Pole starting with these poles we clever humans created a squareish coordinate system for our spherical earth the detailed creation of which I'm going to skip because that's a physics story for a never time that took hundreds of years and needed lots of clocks and to make it official that London rules and Paris rules but anyway this grid is what every modern navigational system uses to get around with the GPS global positioning coordinates it gives but if you were to use your GPS to direct you to the North Pole so that you could experience the planet rotating you in place as the stars circled overhead and you pondered the scale of the indifferent universe and your tiny tiny existence within it if you took out your compass to doublech checkck that the GPS got the spot right the compass points you over the horizon toward another north pole what gives compass well what did you expect a compass is a magnet and magnets follow magnetic fields that's like their only thing it's not a math magnet your magnet compass will take you to the gigantic magnetic field spewing forth from inside the Earth so there are two north poles one for math and one for magnets i mean I guess if you want to be technical about it there are three north poles because the magnetic field the north pole of a magnet points to is the south pole of the Earth's magnetic field because opposites attract but look we're just going to ignore that because this isn't a physics video and there's been enough oh it's the opposite actually already and yes I know you can define more norths but we're moving on there are two norths math and magnets the compass points to the magnetic north and the GPS points to the geographic north they don't have anything to do with each other but for navigation humans have used both one isn't better than the other though math/geographic north is now often called true north which feels a bit like humans picking the new one as their favorite one oh and ships of the seas have stopped using the old magnetic north and now navigate with GPS using the true north even modern pirates but planes and pilots still love the traditional magnet north and we can stop thinking about this because they're pretty close anyway although isn't that kind of weird just how close the unrelated poles are on a planetary scale earth just so happens to have a giant magnet that sort of but not quite lines up with the planet's top and bottom in different universe are these things secretly related and still why would runway numbers change just because they're pointing at the magnet one but not the math one oh no there really is an unavoidable physics video inside this geography video and it's called magnets what's your deal okay we really can't cover everything about magnets because it's just so much but some bits of some metals such as iron generate around them a magnetic field why and how were a mystery for a long time until we discovered that if you take a wire and run a current of electrons through it aka electricity this current also generates a magnetic field around the wire but weirder if you start with a current of electrons and pop them in a magnetic field the current will curve and oh look you've stumbled upon a clue to one of the fundamental secrets of the universe magnets and electricity are two expressions of the same thing electromagnetism that's why in science class you can coil up a wire send a current of electricity through it and the whole thing becomes a magnet one you can make stronger and stronger with each additional coil cuz curving currents are magnets which is why when you cut the current everything drops our just iron magnets are doing the same thing but you need to zoom down and down and down and down to the atomic level to see here an atom of iron has a cloud of electrons each electron with a charge and as they whirl around they create a tiny current and a tiny magnetic field zooming even closer each electron spins and this spin acts like the universe's teeniest tiniest current creating the teeniest tiniest electromagnet okay look whirl around and spin don't mean what you think down here because in the land of quantum words mean nothing there is only math that we're not going to do so just go with it anyway in most atoms all these current created tiny magnetic fields arrange themselves against themselves so it all cancels out to nothing but in a rare few atoms like iron does there happen to be an imbalance that aligns and adds up and thus each iron atom is a tiny magnet and if adjacent atoms align their little magnetic fields add up and zooming out and out and out if all the atoms in the iron are aligned then the iron acts as one big monkeysized magnet but deep down inside it's just electron-sized electromagnets and scaling up and up and up and up to the whole Earth's magnetic field it's an electromagnet all over again see the Earth is made of parts the thin perilous cool crust on which we live the inner solid core that is several thousands of degrees hot a middle mantle mostly solid and relatively cool and critically a ring of metal liquefied by the hot hot core and just as on the surface do hot spots cause convection currents of air to try to even the energy out so too does the unbelievably hot inner core cause convection currents of liquid metal metal that happens to be mostly iron our magnetic friend thus as this mixture circles so do all its electrons curving currents which gets us magnetic fields baby though as individual coils it's not very strong to start to get a planet-sized field you need to somehow stack the coils which is where the Corololis effect comes back in for just as Earth's spin causes convection currents of air into coils so too does Earth spin cause convection currents of liquid metal to coil making the fields stronger turning the whole of the Earth into a giant electromagnet wow if there's one thing the indifferent universe loves it's repeating the same patterns across scales and domains such austere efficiency it's beautiful oh get back to the runways oh unlike a real electromagnet made of stable metal all that swirling liquid iron inside Earth is not stable so at any moment the field can split into multiple magnetic poles roam randomly or diminish entirely before oh my flipping north to south and south to north which it does every couple hundred,000 years or so and we have no way of predicting when great that'll cause some trouble and there's a clue that it's coming because the strength of Earth's magnetic field has dropped 10% over the last couple hundred years which is concerning so uh if you're watching this video after the flip one take everything I said about magnetic north and magnetic south and now it's the opposite actually and two if it's been a couple hundred thousand years since my last upload don't worry that's about normal so be sure to smash that subscribe button so you don't miss the next video oh and hit the bell god I hate that you have to do that now all right time to wrap this up first this giant electromagnet made of liquid metal coriololis convecting inside Earth only semi-sty means Earth's magnetic field moves that finishes with the physics and means the magnet north pole moves and quite a lot on human time scales when we started measuring it was safely inside of Canada but it's recently rocketed north geography over so we can finally get back to the start since runway numbers are derived from the heading on a compass when the magnet north moves the runway numbers need to change to match and the closer your airport is to a magnet pole the bigger a difference its movement makes and thus the more frequently you need to update the number which is why it's no surprise that Canada with more northern runways than anyone was the first to get pretty tired of frequently repainting all her northern runways and so changed her system to be based on the unmoving math north instead but this means when flying over her territories pilots can't count on their compass to match the runways and the winds they can use their GPS assuming the battery is charged but these runway numbers are inconsistent with runways in the whole rest of the world now Canada thinks her system is better and has created an aviation agency to try to convince all her international friends with airports more equatorial and thus less of this problem to try and switch with her from the old and busted magnetic north to the new true north if pirates can do it why not planes too y Well because it's mostly a problem for you and thus there's not one system for numbering runways but two oh hey you if it's your second watch through did you notice this video is a version two with sharp eyes you might have spotted what's changed during the landing at Nook V1 had the runway number repainting go up a number when it should have gone down the opposite actually now after first upload this seemed like only a glitch right causing some confused comments to come in but as I thought about it more it grew to a blunder a blunder that kept bothering me for after all the first half of the video builds towards these two correctly calculating the runway number in advance of their landing before finding the unexpected and then being proven correct which they weren't before the rest of the adventure this mistake brought me much gloom and eventually graduated this glitch turn blunder to an error kind catastrophicus so I've sucked it up sacrificing the V1 view count and algorithmic love of the YouTube gods to probably annoy a lot of people with what looks like a pointless re-upload if you didn't make it to this part post video which most won't but you did so thank you and given that you're a video completionist I've got something extra for all the Bonnie Bees who support the channel a 2-hour stream where I take you behind the scenes on how what I thought would be a simple explanation on runway numbers no more than 3 minutes surely spiraled into almost 20 explaining almost all of physics something given my background as a physics teacher I had been really trying to avoid for years but was obviously inevitable so if you've ever wondered how videos like this come together the stream is an unfiltered look at the process from ideiation to articulation to animation to publication plus revealing all the hidden Easter eggs and references of which there are a ton in this one plus plus there's a deleted scene on how everything connects to the Aurora actually and so if you've made it all the way here to the end of the end of the video you can click here to become a Bonnie B and get access to all of the extras for this video and others as again a thank you for directly supporting what makes these crazy long-term projects even possible thank you