Compasses don’t lead to true north


See the image below? That’s the South Pole, well… the physical pole placed at the geographic South Pole. Here’s the thing though, that’s not the magnetic South Pole, meaning that getting to it with just a compass would be impossible. To find out why, let’s talk a bit about airport runways and how they’re named.

Runway names

Yes, runway names. Unless you have a deep fear of flying, you’ve probably taken off from (and hopefully, also landed on, during that same flight) an airport runway once or twice in your lifetime. You might have also noticed the runway names, which mostly consist of numbers ranging from 1 to 36 combined with letters like L,C and R. These names might not roll off the tongue, but they’re quite important, and have a unique criteria for when airports have to change them.

In 2009, Fairbanks International Airport in Alaska had to rename its runaway from 1L-19R to 2L-20R. This sounds like a rather trivial decision, why would it matter if it were named 1L-19R or 2L-20R? What’s important to know here is that runways get their names from the Earth’s magnetic field. Let’s take out a compass to explain.

A compass is divided into 360° degrees and has an arrow that points to magnetic North in one direction and magnetic South in the opposite direction – 180° in the opposite direction, to be exact. Runways are named depending on their orientation to magnetic North. For example, 1L-19R is one runway that has two sides. On one side, it’s called 1L. To keep things simple, the names are based on the direction they point to in degrees, rounded to the nearest ten and excluding the final digit. So the 1 in 1L stands for 10° degrees after being rounded, while the L stands for left. Airports use letters like L,C, and R as shorthand for left, centre and right, to differentiate between different runways that point in the same direction.

https://commons.wikimedia.org/wiki/File:Compass_align.jpg

If I haven’t lost you yet, let’s see why the same runway is called 19R from the other side. If a plane would land from the other side, that would mean that its going in the exact opposite direction, so 180° in the opposite direction. We’ve established that the runway has a position of 10°, so we just add 180° and then we leave out the final digit, leaving 19. Since we’re on the other side, its now 19R, meaning the runway on the right.

Now that we’ve gotten that out of the way, let’s get back to our story.

Compasses don’t lead to true north

The reason Fairbanks International Airport had to rename its runway, if you haven’t guessed it yet, is because the earth’s magnetic field changed. Not by a lot, but by just enough to require an entire runway to change its name and pilots to take note. And this isn’t a one-time occurrence, but something ongoing that affects places closer to the South and North pole. This is one of the few tangible situations where the Earth’s magnetic field affects day to day life…so far.

Or rather, this is one of the few examples of the Earth’s magnetic field changing that we will see in our lifetimes. If you aren’t aware, there’s plenty of research showing that the magnetic field doesn’t just change by a few degrees, but it even flips once every few hundred thousands years. That’s when North becomes South, and South becomes North. This won’t only happen, but has happened hundreds of times already.

I brought up the South Pole for a reason. It’s physical, it’s there, you can touch it, see it, take pictures of it or selfies with it. But it should never be confused with the magnetic South Pole, which is constantly moving. The picture represents the Geographic South Pole and is based on the Earth’s axis of rotation. It’s also known as true south, the same as the Geographic North Pole is known as true north.

The actual Magnetic South Pole is currently about 2,860 km from the geographic one, while the Magnetic North Pole is harder to pin down since it is located in the middle of the Arctic Ocean. What we do know, however, is that the speed at which it is moving accelerated from 9km/h to around 52km/h from the 1970s to the 2000s.

If that’s not impressive, there’s at least one thing you should take away from this. Anytime someone says their “compass is pointing towards true north”, whether its literal or metaphorical, you can tell them they’re wrong. Compasses only point towards magnetic north, which is always on the move.

Photo Credits: Cover, Compass, Runway, South Pole

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About Radu Mester

Radu studied film & computing, works in EdTech as a content creator, and reads nonfiction books in his spare time.

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