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But the meridians of longitude define time zones

The lines of longitude define time differences, but they merely suggest time zones. A quick glance at a map verifies that they don't define time zones. Political entities define time zones.

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accurate east/west navigation had to await the arrival of the chronometer.

Actually, you can measure longitude using only celestial navigation (using the lunar transit method), but you need detailed astronomical tables (plus clear skies, a steady quick hand, and no little mathematical skill) to do it, and the available tables were made from observations taken at Greenwich; hence one had to calculate one's position relative to Greenwich, making Greenwich the origin of the coordinate system. If the best tables were made from observations done in, say, Berlin the prime meridian would go through Berlin. The prime meridian goes through Greenwich not because of British leadership in boats and trains, but in astronomical observation.

Yes, lines of longitude define time differences, but sailors weren't interested in determining when it was tea time in London or when to telephone a friend in Chipping Sudbury, they interested in determining where the hell they were.

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The lines of latitude are defined by the Earth; longitude is defined by man.

Both sets of lines are defined by man. There are is no reason why the lines of latitude should be shown as they usually are on world maps - they could be shown to be a thousand miles apart or half a mile. Longitude meridians are conventionally drawn at 15 degrees as that is the distance that the Earth rotates in an hour. Convetion only; there's no physical reason why an hour should the length it is.

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Actually, you can measure longitude using only celestial navigation (using the lunar transit method), but you need detailed astronomical tables (plus clear skies, a steady quick hand, and no little mathematical skill) to do it,

True. But it was not a very accurate method at sea for the reasons you cite. To read the time off a Harrison chronometer was far simpler.

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Richard: Plus it was Britain that invented railways and it was railways that invented the concept of universal time. Before the railways locations set their own local times according to the sun's position.

I see. By that logic Richard will give the British credit not only for the railways, but for everything that the railways resulted in.

Let's be accurate here. As to railways:

• Britain did not invent railways. Carts-on-rails had long been used in the mines, moved by animal power.
• Britain was the first pioneer in the use of mechanical power (steam engines) to move containers over rails.
• The British system tended to be based upon heavy investment in well-graded track, allowing the use of relatively low-powered engines. British firms, having established markets, could justify that investment. In the U.S, however, it didn't make sense to spend heavily for laying track to a newly-opened market. The U.S. system tended toward lesser track-grading and, consequently, required and received the development of higher-powered locomotives.

As to time zones:

• In 1883 that the U.S. railroads switched to a zoned time system. (Previously each locality had its own local time, based upon the sun.) While this was a special "railroad time", in practice the general population along the rail route reset their watches to railroad time.
• I believe it was the next year, 1884, that the UK started to use a standardized time across the country. In any even, it was not until 1884 that much of the world in general switched to zoned time.

As to the prime meridian:

• As of 1884 the Greenwich meridian was the most common, but by no means exclusive, choice for sea measurements; it was less dominent for land measurements.
• At an 1884 conference in Washington D.C., called by the U.S. President, much of the world agreed to use the Greenwich meridian.
• A prior 1874 Rome conference had reached no binding decision but had ended in a statement of hope that the world would standardize to the British meridian and that Britain would covert to the metric system.

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Both sets of lines are defined by man.

The equator is defined by the axis of rotation of the Earth. Nobody had to decide where to put the equator or the poles. That's why latitude is easy to measure and longitude hard.

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I believe it was the next year, 1884, that the UK started to use a standardized time across the country. In any even, it was not until 1884 that much of the world in general switched to zoned time.

This is the point I was trying to make about "railway time". Zoned time didn't happen until the railways spread across the world; prior to that, even though navigation relied on time zones defined by meridians of longitude, different cities used different times based on the solar time in their area.

Interestingly, in England, "legal" time differed from standard time for many years (I think until the 1920s) following a judicial decision that the time followed by the court would be the time on the court's clock - which was the solar time, not "railway time". Or that's the story I learnt - I haven't checked it out.

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The equator is defined by the axis of rotation of the Earth. Nobody had to decide where to put the equator or the poles. That's why latitude is easy to measure and longitude hard.

Those points are defined, as you say - but it was a human decision to subdivide them into degrees (they are equidistant and could equally well be divided into miles, chains, furlongs, rods, poles or perches). And the degree is an arbitrary division itself; a circle does not have to be divided into 360 degrees; 512 degrees would be a far more logical division.

There is also some logic in the suggestion that two of the defining parallels should be the tropics of Cancer and Capricon, presently at 22.5 degrees, which could be placed at a precise distance rather than a fractional number of degrees. Or, had a cirle been divided into 512 degrees as I hypothesisied above, then the tropics would have been at a more comfortable 32 degrees.

Because we know the present system and it works well, it's hard to imagine any alternative. But the divisions we now know and accept were not inevitable neither are they unalterable.

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the tropics of Cancer and Capricon, presently at 22.5 degrees

That's 23.5 degrees.

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it was a human decision to subdivide them into degrees (they are equidistant and could equally well be divided into miles, chains, furlongs, rods, poles or perches)

I don't believe anyone has claimed otherwise.

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512 degrees would be a far more logical division

Spoken like a true Brit! Now I know why we have miles, chains, furlongs, rods, poles and perches, not to mention grains, pecks, slugs and stones.

Our 360 degree system, by the way, dates from the Babylonians and is the oldest system of measurement still in use today. It is superior to a 512 degree system because 512 can only be divided by multiples of 2, while 360 can be evenly divided by 2,3,4,5,6,8,9,10,12,15,20,24,30,40,45,60,90,120,180 and a few I missed in between. That's why they used it: easy to make fractions.
Also, I've heard that the coordinates of celestial objects are still made in the system that the Babylonians used, but I've never confirmed that.

To return to our muttons, one suggestion I saw recently for Pluto et al. was to call them planettes.

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That's 23.5 degrees

Well, the darn things keep moving.

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one suggestion I saw recently for Pluto et al. was to call them planettes

Maybe it's the Mexican heritage of California, but I prefer planitos. ...mmmm....planitos...

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Planitos? I think I had them at Taco Bell recently.

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That's 23.5 degrees

Oh clang:-( Do you know, I didn't even bother to check it so sure was I of my memory!

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It is superior to a 512 degree system because 512 can only be divided by multiples of 2

True. But 512 can be halved in full numbers down to 1.

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I didn't even bother to check it so sure was I of my memory!

22.5 is half of 45, maybe that's why it sounded familiar. The Earth wobbles on its axis between 21.5 and 24.5 degrees over a roughly 40,000 year period, so you'll be right eventually (the tropics of Cancer and Capricorn oscillate concomitantly, of course).

There's a word for that sort of wobbling. What is it?

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There's a word for that sort of wobbling

The angle of the axis is called the Earth's obliquity. I haven't found a word for the cyclical change of obliquity.

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Originally posted by Richard English:
True. But 512 can be halved in full numbers down to 1.

Yes, but how is that of use in astronomy, or in math? Or for that matter slicing pies? It is useful for the number to be divisible by multiple prime numbers.

No number can ever be divisible by every smaller number so any number will be a compromise. I'd have though that a number that's perfectly divisable down to 1 would be the most useful.

But in any case, whatever number is chosen it will arbitrary and a human decision. There are no "natural" measurements; all depend on mathemical systems devised by different peoples, at different times, using different rules.

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I'd have though that a number that's perfectly divisable down to 1 would be the most useful.

Actually, any number is perfectly divisible down to one. Just divide it by itself, and you have "1".

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But in any case, whatever number is chosen it will arbitrary and a human decision. There are no "natural" measurements; all depend on mathemical systems devised by different peoples, at different times, using different rules.

I suspect that we have a confusion of semantics. Agreed that all measurements require a human decision or choice of how to measure. But that does not mean that no measurements are "natural" and all are "arbitrary". The periods of time we call a "year" and a "day" are defined by naturally-occuring events (the revolution and rotation periods of the earth). It was of course man's choice to use these naturally-occurring periods for his measurement -- but it was hardly an "arbitrary" choice.

Apologies. I should have defined "measurements". I was talking about linear and radial measurements - which were the ones under discussion.

Clearly measurements of time are different since we do have the rotation of the earth as a basis. Having said which, most of the subdivisions of the year are also abitrary. Only the month has any real periodic basis.

Nathan Bierma had a good column today about the planet definitions. Quoting Benjamin Zimmer from Language Log, he says that it's hard to exclude Pluto as a planet by using a term with the word "planet" in it. Bierma quotes Zimmer as saying, "The fact that the IAU would like us to think of dwarf planets as distinct from 'real' planets lumps the lexical item 'dwarf planet' in with such oddities as 'Welsh rabbit' (not really a rabbit) and 'Rocky Mountain oysters' (not really oysters)."

Here are some interesting Pluto-less mnemonics from Language Log. I think I could do without the Michael Jackson one.

[BTW, I have linked to Bierma's "On Language" columns a lot, and I do like him. However, I went to his Web site tonight and found that he graduated from high school in 1998 with a bachelor's degree in communication and journalism. I had thought he had more of a linguistic background, and maybe was a bit older. ]

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Oh THAT Michael Jackons. I though you meant the REAL Michael Jackson - the beer writer!

Speaking of Pluto, we really must be politically correct and include the Plutonians in on this decision, as this recent FoxTrot comic says.

[I just don't know how to post those comics like the rest of you can, so the above link was the best I could do. Sorry!]