World Building Question: Where Am I?


Last time in the World Building Questions I talked about the differences between noon, 12pm, and how those two concepts evolved. In doing so I very briefly touched on Universal Time, offsets, and the fact that timekeeping on the globe centers on a spot to the south-east of downtown London just off the Themes River. This is Greenwich, specifically the Royal Observatory therein. More specifically, the line running up the middle of the front door to the roof peak overhead. This is the origin point for Greenwich time, and it serves as such because the British figured out Longitude at sea first. Which has a lot to do with noon. So there’s a fitting transition from asking questions about how we keep time on planet earth to how we keep directions.

Let’s talk generally about the ideas of latitude and longitude first. The earth is a sphere. That’s the first of several lies in this post, but it’s an extremely helpful lie.¬† Around this sphere humanity has drawn two imaginary lines and defined these as origin lines. One is the equator, the other is the Prime Meridian. Locations are then defined by how far north or south they are from the equator, and how far east or west from the Prime Meridian, given in degrees. On earth we call these two measurements latitude and longitude, respectively. Lines of latitude circle the globe, parallel to the equator. Lines of longitude run pole to pole, converging at each end.

The equator is a pretty easy and logical defining line, it’s a circle around the earth perpendicular to the axis of rotation where the days don’t really vary in length and equidistant from the poles. To determine how far north or south of the equator you are, whether at land or at sea, simply look at the sky. For centuries, ancient navigators have known which heavenly bodies to consult and measure to know just where they are in relationship to the equator. The problem is…once you know your latitude is 20 degrees north of the equator, that’s great, you’re somewhere on 19,250 mile long line circling the earth. Where on that line are you? What’s your longitude?

Longitude is harder to work out that latitude. There are no clear celestial signs for how far east or west one has traveled. The easiest way to work it out is through a clock. Here’s how. First you find a clock that keeps reliable time. Then you set that clock to 12pm when the sun is directly overhead. Now, start traveling east or west until noon the next day. Noon, not 12pm on the clock, I’m still being serious about that distinction. When the sun is overhead, look at your clock, and you know how far east or west you’ve traveled by the time shown. How?

Well, it takes 24 hours for the sun to circle the earth. A circle is 360 degrees. If you divide 360 by 24 the result is 15 degrees. So, for each hour that the clock is off, you’ve traveled 15 degrees of east or west latitude. If the clock shows a time before 12pm, you’ve traveled east, if it shows a time after 12pm, you’ve traveled west.

There you have it. Noon tells you where you are. Segue complete!

Alright, it’s a little more complicated than that. Not the math, the math is simple to derive. The difficulty is in that first step: finding a clock that keep reliable time. That’s not too difficult in the year 2013, however clocks of a sufficiently reliable accuracy are a relatively new invention. Clocks of a reliable accuracy that will retain that accuracy while at sea are newer yet. And here is where I’m going to reference A History of the World in 100 Objects, a fantastic podcast and audiobook and hardback that I’ve talked about on this blog before. If you’re curious about history, grab this! The 100 objects range from millions of years old to only three years old, presented chronologically. Object 91 is a ship’s chronometer from the HMS Beagle voyage that brought Darwin to the Gal√°pagos Islands.

What John Harrison did was to invent a clock, a chronometer, that would go on accurately telling the time set in Greenwich, despite the constant movement of the ship and, just as important, despite any fluctuations in temperature and humidity. It was a great feat of precision engineering, but Harrison’s chronometers were pioneering, high-quality instruments, made in tiny numbers and affordable only by the Admiralty. Then, around 1800, two London clock-makers managed to simplify the mechanisms of his chronometer, so that virtually any ship – and certainly the whole of the Royal Navy – could carry them as routine equipment.

First Sea ClockThe image over to the right is one of John Harrison’s first clocks intended for use at sea, not one of the simpler devices that followed. It is the Creative Commons released image I could find.

So this is all well and good, there’s some nice math involved, and I like math. But why is the Prime Meridian where it is, and not one of the infinite other equally arbitrary lines of longitude? When I made that post about noon, I said that the Greenwich Meridian was the Prime Meridian “because an Englishman figured out longitude at sea.” I was London clock makers who perfected the ship’s chronometer, it was the Royal Navy that first used it, and they needed a point to use as their baseline when setting all the chronometers that would go on all the ships. So they chose the Royal Observatory in Greenwich.

It doesn’t entirely answer the question, though, as it only explains why the British chose the Greenwich Meridian. Why did the rest of the world accept this meridian? Simple. They voted on it. In 1884 a conference was held in Washington, DC for the purpose of defining which arbitrary north-south line would be the arbitrary north-south line. 26 nations were invited, 22 voted for the Greenwich Meridian, and the motion passed.

Do I even need to say that the French were one of those opposing. They used their own meridian which ran through Paris, and kept it until 1914. Which means the Prime Meridian has been an international standard for less than a century. Which makes it slightly older than the full international adoption of the modern calendar, but puts it squarely on the list of things you might have thought were international standards longer than they actually have been.

One equator, one Prime Meridian. That’s also how we can know where we are on an arbitrary, but internationally agreed upon, scale of latitudinal and longitudinal measurements. Certainly we now have more sophisticated ways of determining our location, such as GPS, but it all comes down to clocks and the sun.

How do you know where you are at sea without a way to calculate longitude? Answer is, you don’t. Not really. Oh, the best navigators could guess by using a process called dead reckoning which relies on knowing three things: where you were, what heading you were on, and how fast you were going. If I traveled 50 nautical miles east-northeast, I can put a dot on a map 50 nm east-northeast of the dot I drew yesterday. Which was based on the dot the day before. And the day before that. It’s a series of educated guesses which allows errors to compound. Yet it brought Columbus to the new world and back again.

I’ll admit, while a fun transition from time to direction, this is a harder post than usual to come up with world building questions for.

I could posit a planet in tidal lock to its sun has an interesting set of non-arbitrary meridians. It has an equator, and it has the delineation between day side and night side. Since the sun doesn’t rise or set, its position in the sky would always provide an exact location on the day side. The night side would have to rely on purely stellar navigation. This is actually the case in Frederick Pohl’s book Jem, which has a “heat pole” and a “cold pole” instead of a North and South pole, representing the points farthest from the day/night line.

I could posit an uninhabited alien world. Would a human colony on a new planet use its first outpost to define a prime meridian for the planet?

I could posit an inhabited world. Would an alien race come up with another way of defining a point on their globe? I can actually think of one. Start with the equator around the center of the globe, then rotate it a given number of degrees about a set axis. A point on the globe could be defined by the angle of rotation and the distance from the equator. I’m not sure that makes sense as I’ve written it, I might try to diagram it if it doesn’t.

I suppose the world building lesson is that north and south, as we define them, are easy on a rotating body. East and west are a little harder. A society that navigates with something like latitude would need a way to compute that latitude, whether technical, biological, or magical.

Up next: how maps are centered and oriented (“Which way is up?”), and how we tell directions on a day-to-day basis, especially since we have two different sets of four directions we tend to use (“Is that my right, or your right?”).

Chronometer picture via Wikipedia user Phantom Photographer and released under Creative Commons 3.0 Attribution-Share Alike license.
  1. No comments yet.
(will not be published)


%d bloggers like this: