Why Did Longitude Matter?

Latitude and Longitude

Longitude. You know it, you love it, you probably don’t care about it at all. But what if I told you that calculating longitude at sea was one of the most important problems in the world a few hundred years ago?

It was so important that England would give the equivalent of $6 Million in today’s money to anyone who could solve it. In comparison, solving one of the Millennium Prize Problems (which includes the famous P vs. NP problem) would only award you with $1 Million.

Let’s step back for a second. What even is longitude?

Lines of longitude are drawn across the earth from the north pole to the south pole. They’re all the same length.

This is in contrast to lines of latitude which are parallel and varying in size. Latitude is largest at the equator and smallest at the poles.

Latitude tells you how north or south you are, while longitude tells you how east or west you are, which is particularly useful if you just happened to discover a shiny new continent with gold on it somewhere to the west.

We will get into why in another post, but for now all you need to know is that up to the 1700s, longitude was more or less impossible to calculate at sea with any reasonable accuracy.

The Problems Of Not Knowing Longitude

When there’s no good way to calculate longitude, you have two choices as a sea captain.

Rely On Latitude

Latitude Meme

Firstly, you can rely entirely on latitude. Longitude may have been hard to calculate, but latitude was easy. Therefore, one solution to the longitude problem was to hold on to a specific latitude for the entire trip, or use a well mapped route that you could navigate with only latitude.

The problem? These were well mapped routes. So they were heavily trafficked. Do you know who likes heavily trafficked routes with valuable cargo? Pirates, and enemy nations.

If you want to avoid pirates and foreign interference, you probably want to avoid the mainstream path.


Drake Meme

The other thing you can do is to say YOLO. You can use methods of calculating longitude that aren’t completely reliable, but kind of work as a guesstimate.

Or you can just follow your heart, and pray that God is on your side.

This actually kind of worked, though sometimes it would lead to captains getting lost, running out of supplies, or crashing into rocks and dying.

Samuel Pepys summed it up nicely in 1683:

“It is most plain, from the confusion all these people are in, how to make good their reckonings, even each man’s with itself, and the nonsensical arguments they would make use of to do it, and disorder they are in about, that is by God Almighty's Providence and great chance, and the wideness of the sea, that there are not a great many more misfortunes and ill chances in navigation than there are.”

In the next post in this series, we’ll talk about why longitude was so hard to calculate, and the various calculation methods people experimented with.

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