How to Use the Stars to Find Your Latitude

Have you ever wondered how people figured out their latitude back in the days before the Internet? Did you know you can use the same math trick they used to pinpoint your latitude today? Keep on reading to find out how it works.

Jason Marshall, PhD,
Episode #252

Map of EarthGreetings, Secret Agent Math! Your mission, should you choose to accept it, is to figure out where you are on Earth relative to the equator. Why might you need to be able to figure this out? Who knows! But a secret agent like yourself is always curious to learn new things, right? After all, you never know when one of these skills is going to come in handy.

Perhaps it’ll be when you’re on that super secret mathematically-oriented spy mission to crack the code used to encrypt that really important message. Or perhaps it’ll be when you’re deploying your particularly well-honed set of mathematical skills to solve that riddle that’s going to help you save those people from that thing. Or … whatever.

The point is, you never know when figuring out where you are on Earth relative to the equator—by which I mean figuring out your latitude—is going to come in handy. So, as every good secret agent skilled in the fine and beautiful art of mathematics has done before, today we’re going to add this trick to our repertoire. Stay tuned to find out how it works!

Recap: What Is Latitude?

Before we rejoin Secret Agent Math and the quest to pinpoint your latitude on Earth, we’d first better recap what we mean by latitude. Those of you who have stared at a globe long enough to notice the grid of horizontal and vertical lines already know pretty much everything you need to understand latitude (as well as its close cousin longitude).

We can mark the location of any point on Earth by specifying its latitude and longitude.

The key thing to know is that we can mark the location of any point on Earth by specifying its latitude and longitude. Lines of constant latitude run around the globe parallel to the equator, while lines of constant longitude run north-south from one pole to the other.

Today we’re going to focus on how you can figure out the latitude of wherever you happen to be standing. In other words, we’re going to figure out how you can find the number of degrees north (or possibly south) of the equator that you are standing. Ready to hone your math secret agent skills and figure it out? Good! 

The Boring Way to Find Your Latitude

Like most things you might want to do in life, there's more than one way to find your latitude. Some ways are easy but boring, and some are a bit harder but much cooler. For the sake of completeness, let’s start with the easiest but also the most un-Secret Agent Math way. Namely, just ask Google.

Yes, that’s right. If you are dying to know your latitude on Earth at this very instant (and who isn’t) and you just can’t bear to wait, you can go to Google and enter something like “latitude of Los Angeles” (or whatever city you’re in). In its nearingly infinite wisdom, Google knows these sorts of things—and it's happy to tell them to you. Google tells me that my hometown of Los Angeles is located at a latitude of 34.05º N … that's about 34º north of the equator.

While kind of boring and totally not something a secret agent would use, this trick will nonetheless tell you your latitude wherever you are on Earth. That's certainly cool, but we can do much better.


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