1675, Charles II appointed  John Flamsteed as the first King’s Astronomical Observator, a.k.a., the Astronomer Royal. For that he got £100 a year, use of the brand new, empty Greenwich Observatory, and no equipment. What a deal! He organized some equipment, supplied whathe couldn’t get donated himself, took on students to stretch his income, and set about studying the sky, which was the key to accurate navigation. This mattered intensely because Britain was increasingly a naval power. That makes this a story about power and money and empire, although they’re not what I’m going to tell you about. Brush the words aside, though, and you’ll find them right under the surface.

Flamsteed had come to Charles’ attention by working out a formula for converting solar time to mean time, and for that to make the least bit of sense, we need to take a step or six back, to the time before time was standardized. But before we do, let me sneak in the information that Flamsteed did something at Greenwich that will become central to our story: he drew an imaginary line right through the place and claimed it as the world’s prime meridian–the line that would divide east from west the way the equator divides north from south. 

At the time, the only people who cared were astronomers. Everyone else measured east and west from wherever they were standing and life rolled on as if nothing had changed.

Vaguely relevant photo: Navigation at sea comes into the story. Do I need to tell you this is the sea?

Clock time and solar time

For those of us who grew up with clocks–and I’m guessing that’s all of us–it goes against the grain to think that the hour hasn’t always been a fixed measurement, but it hasn’t, and this makes a certain kind of sense. As soon as you wander away from the equator, the day’s length varies over the course of the year, and–oh, hell, you know this–in the interest of domestic harmony, so does the night’s. So when people decided it would be convenient to divide the day into twelve equal segments and the night into twelve more, they came up with segments that were the same in the morning, at night, and at noon but that shifted over the course of the year, following the stretch and unstretch of the day.

Why twelve segments? Don’t ask. It’s what they did. Or at least what they did in the ancient Middle East. What they did elsewhere is on a different page of the book and I don’t have time to read it just now.

That system held until the astronomer, geographer, and mathematician Hipparchus (120 to 190 BCE; you’re welcome) realized that if he couldn’t find a more reliable way to divide time his brain would melt, so he took hold of the equinoxes, when day and night are equal, and measured the length of the segments, and said, “That’s it. This is the length of an hour.”

Only since he was Greek and ancient, he said it in classical Greek. And no, I’m not going to translate.

It was a brilliant idea and everybody who wasn’t a mathematician, astronomer, or some sort of specialist ignored it. Daylight went right on lasting for longer and shorter periods of time over the course of the year and in practice so did the length of an hour. And people kept on using those expandable, contractable hours until–oh, let’s say the 14th century, when mechanical clocks ruined the fun.

And that, children, is the difference between clock time and solar time.  

Hipparchus did one other thing that we need to know about: he introduced longitude and its non-identical twin, latitude. Between them, they kept geography from being as slippery as hours.

Longitude

Even after an hour in May had been strong-armed into being the same length as an hour in January, time was still slippery. Everyone could agree that noon came in the middle of the day, but the middle of the day came at different moments in different places, and people set their clocks to local time.

Well, what else would they set it to? Since transportation was slow and phones didn’t exist, hardly anybody cared and I’m willing to bet not many people even noticed.

The people did care, though, were sailors, because you need two fixed points to calculate your longitude. Or to put that in plain English, to figure out where the hell you are, and I’d love to explain why and how but it’s way above my pay grade. 

Knowing where you are is less of a problem on land, since you have, ahem, landmarks, and fixed points stay politely fixed, but at sea they’re badly behaved, and the difficulties this posed crashed into public and political awareness in 1707, when four British ships wrecked off the Isles of Scilly and 1,400 lives were lost, all because, through no fault of their own, they hadn’t been able to calculate their position reliably. 

Now let’s circle back to Flamsteed and his imaginary line through Greenwich. It was a fixed point that ships could compare their location to. If I understand this correctly–and that’s not guaranteed–they could use solar time at their location and compare it to clock time at Greenwich. All they needed was a clock they could set to the time at Greenwich. 

Nothing to it, except that the clocks of the era couldn’t keep time on a ship that was going up, down, and sideways. 

At more or less this point, Parliament offered a £20,000 prize–that would be something like £2 million today; in other words, more than enough money to hold people’s attention–for the person who could invent a seaworthy clock, and in 1773 John Harrison, a joiner and watchmaker, did just that. All sailors had to do after that was set it to the time at Greenwich and as long as they remembered to keep it wound they had their second fixed point. 

Greenwich Mean Time

For some hundred years, ships used that imaginary line as their ultimate reference point. Think of it as Patient Zero of the world’s time zones.

As the railroads grew, treating time as a liquid began to became less and less workable on land, and Britain’s railroads introduced Railway Time, which was basically Greenwich Mean Time under another name. Localities were welcome to adapt it or not, but since the trains ran on Railway Time, I expect there’d have been a good bit of pressure to reset village and town clocks so people could catch them. 

In 1880, Britain adopted Greenwich Mean Time as the national time.

In1884, the international Global Meridian Conference accepted the imaginary line through Greenwich as the world’s prime meridian. By then, the US had already based its time zones on it and 72% of the world’s commerce used sea charts that relied on it. But the conference’s acceptance didn’t commit individual governments to doing anything they weren’t already doing, and most of them didn’t.

Then the Titanic met the iceberg–this was in 1912–and it turned out that a French ship had radioed a warning of the danger, but it based its time on the Greenwich meridian and its longitude on the Paris one. The article I found that says said it wasn’t “the overall cause of the disaster,” but it made a hell of a good argument for getting everyone to use the same system and it actually swung a few more countries behind it.

The original imaginary line is now marked in brass, making it a real line, even if it’s not exactly the line that’s in use anymore, In the name of accuracy, efficiency, and confusion, it’s been nudged sideways a few times. Never mind, it made its point.

These days, international standardized time is called Coordinated Universal Time. And Greenwich Mean Time? It’s been downgraded to a simple time zone.