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A Time for Longitude: Navigation Solved

All were lost—always. We listen in awe to stories of the great ocean explorers and navigators from times past, but the fact is, they never really knew where they were. Those shiny brass nautical instruments that no one really understands only provide some of the information required to figure out where you are. To fix your position on the big blue ball, you need to know both your latitude (how high or low on the ball you are relative to the equator and poles) and longitude (how far around the ball you’ve traveled from some defined starting point). As we’ll see, the former is easy to figure out and ruled by the laws of nature. The latter is somewhat arbitrary and gave humanity fits for centuries.

The Problem Illustrated

Suppose we’re driving west on Route 27 to see the world’s largest ball of twine in Cawker City, Kansas and have the following directions. “Keep driving west until you see it. You’ll know you’re halfway there when you see the International Horned Toad Museum on the left.” During the day, this would present no problem. It might take you 10 minutes or hours, depending on how fast you’re driving, but the visible landmarks will help you reach your destination, and once you see the halfway landmark, you’ll have a vague idea of how far you still have to drive. You can figure out how long you have yet to travel based on your speed and how long it took to reach the halfway mark.

Now imagine doing the same navigation in the pitch dark with no headlights. Oh, and your speedometer is broken. You might see a couple of Taco Bells, but you’d drive right on by the World’s Largest Ball of Twine as it and the museum both close at 6 PM and would be dark. You’d have no way of knowing where exactly you are relative to your destination. You might have miles yet to go, or perhaps you already passed it.

Ocean navigation was much like this back in the day.

The problem of finding the world’s largest ball of twine in the dark boils down to time and velocity. If you knew it was 30 miles away from your current location, you could use your speed and time elapsed to calculate your position and remaining distance. If careful with the math, you could (in theory) blindly turn left at the precisely calculated time to enter the parking lot, even if it wasn’t visible. Ever see that movie, Hunt for Red October? Sean Connery did something like that while navigating through underwater canyons in a submarine.

And therein lies the problem faced by, well, everyone sailing the seven seas back in the day. With no reliable speedometer, accurate clocks, or visible landmarks, you really didn’t know where you were, much less when you’d arrive.

Changes in Latitude, Changes in Longitude

Latitude is easy in comparative terms. Earth is mostly round but a little fatter around the middle, thanks to its rotation. While the equator is still an arbitrary line, there’s some substance behind its location. It’s equidistant from the north and south poles, and at noon along equator locations, the sun is directly overhead. As you define latitude lines, you create concentric circles decreasing in size as you get closer to the poles, and those lines are parallel—never intersecting. Wherever you are on Earth, the distance to the next latitude line is consistent.

Longitude lines are different. Not only do the run from pole to pole, they’re not parallel. At the poles, longitude lines touch. At the equator, they’re as far apart from each other as they can get. So, at different latitudes, you’ll have different distances to the next longitude line. So longitude lines represent relative “distance” around the sphere of Earth.

But the big deal for this discussion is longitude demarcations have no natural “starting” position. The beginning of longitude measurements could start in a line passing through Toad Suck, Arkansas or Narvik, Norway. It just doesn’t matter. Longitude lines measure how far around our sphere we’re located from any arbitrary starting point of longitude definition. Today, we use a line passing through the Royal Observatory in Greenwich, England. That line, running from pole to pole, right through the observatory break room, is what we call zero degrees longitude. Besides defining location, this line is the anchor for time zone definitions around the world.

Does Anybody Really Know What Time It Is?

Here’s where things get interesting. It’s fairly easy to determine when it’s 12 noon wherever you are. By definition, the Sun is as high as it can get in the sky. Unless you’re on the equator, it won’t be directly overhead, but there’s always a “highest point” on the arc determined by your current latitude. So, even before the era of quartz watches, it was fairly easy to get an accurate fix on the time of 12 noon by looking up. Even with an inaccurate shipboard clock, early navigators could re-calibrate it every day at noon, so it only had to keep somewhat accurate time for 24 hours.

Time for Longitude Position

Now, consider that a day has 24 hours, and this is defined by the rotation of the earth, so a longitude position could be defined by knowing the time at whatever place we defined as zero longitude. If we know it’s 12 midnight in Greenwich, England, and it’s noon wherever we are, then we must be precisely halfway around the world from the starting point of Greenwich.

Since the earth rotates, time represents distance around the globe. Every hour, we rotate 15 degrees around as defined by 360 degrees for a full rotation divided by 24 hours.

So, one way to accurately figure out your longitude position is to have the ability to keep “home” time precisely on the ship so you know the time from your starting point and the time where you are right now. While land-based clocks have been fairly accurate for centuries, it was much harder to keep accurate time at sea. Pendulum clocks, like the big Grandfather versions, can keep time within a minute per day but don’t do so well in the rocking motion of a boat. Salt air, humidity and changing temperatures also wreaked havoc on old mechanical timepieces.

Time for Big Money

In the age of intrepid explorers and folks out to make big bucks in global trade, knowing position while at sea was a very big deal. In fact, it was frequently a matter of life and death. In 1707, a squadron of British ships ran aground, resulting in the deaths of over 1,000 sailors because the ships were closer to land than predicted. The bottom line was that Admiral Cloudesley Shovell and his navigators couldn’t determine precisely where they were.

To overcome the navigation problem, governments began offering cash prizes for solutions to the longitude navigation problem. Kings Philip II and III of Spain started in the 1500s, followed by Holland, and by the 1700s, England.

By the 18th century, two methods were in serious contention for the money: the use of lunar distance, relying on celestial observations, lots of data tables, and hours of calculation. The second method was simply figuring out how to keep accurate time. To get a usable longitude fix, seaboard clocks had to be accurate to within several seconds per day—a seemingly unattainable feat at the time.

Enter John Harrison

Leave it to a crafty carpenter and clock-maker to persevere in the workshop. No, his name wasn’t Joe Timex, but rather John Harrison. Creating a series of five chronometers aptly named H-1 through H-5, it was iteration H-4 that won him the English prize.

Not surprisingly, the powers to be got all tight-fisted when Harrison finally succeeded in solving the longitude problem in a practical way. Because politics. After taking his claim to Parliament, he finally got the cash in 1773.

Final Analysis

It pays to wear a watch.

But seriously, until the advent of modern positioning methods like GPS, it was simple timekeeping that enabled accurate global navigation. A fix on the time and some very simple math changed the world as we know it. The next time you meet a clockmaker, buy them a cookie.

Editor’s Note: There is a stellar book on the topic of longitudinal navigation. I know it sounds boring, but I guarantee you it’s a great read. You can pick up a copy here.

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