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September 28, 2005

Reality Based Time
Posted by Jim Macdonald at 10:10 AM * 68 comments

To begin with, twenty-four hours in a day and 360 degrees in a circle are arbitrary numbers. But they lead us to the question: What time is it?

People like patterns. Recognizing patterns allows planning. Planning has led to a lot of things, and arguably our success as a species is one of them. So folks noticed that the sun came up every day, set every day, and came up again the next morning, pretty much in the same place it came up the day before.

Higher and higher every day
Till over the mast at noon…

Noon is when the sun makes its meridian passage — when it’s due south (if you’re above the Tropic of Cancer) or due north (if you’re below the Tropic of Capricorn). That’s what we navigators call “LAN” or “Local Apparent Noon.” (Meridian comes from the Latin medius, middle; dies, day — the middle of the day.)

If you’re between the Tropic of Capricorn and the Tropic of Cancer, this is a bit trickier. The sun could be directly overhead. The Tropic of Cancer (in addition to being a book by Henry Miller) is 23.5 degrees north of the equator. The sun is directly overhead there when it’s in Cancer. The Tropic of Capricorn (aside from being another book by Henry Miller) is 23.5 degrees south of the equator. The sun is directly overhead there when it’s in Capricorn. (And you thought that those hours reading the newspaper horoscopes would never come in handy.) The area between the two Tropics is called “the tropics,” and a hot, nasty place to live it is, to be sure.

Anyway … back a long time ago, perhaps in Babylonia (hah! An Iraq reference! This post wouldn’t be complete without one!) someone decided that there were twelve hours in a day. Twelve is easily divisible by one, two, three, four, six, and itself … so it’s a good number. A natural day runs from sunrise to sunset. That’s the “natural day” that Dr. Faustus is carrying on about:

Now hast thou but one bare hour to live,
And then thou must be damn’d perpetually!
Stand still, you ever-moving spheres of heaven,
That time may cease, and midnight never come;
Fair Nature’s eye, rise, rise again, and make
Perpetual day; or let this hour be but
A year, a month, a week, a natural day,
That Faustus may repent and save his soul!

The natural day was divided into natural hours, twelve from sunrise to sunset, another twelve from sunset to sunrise. In northern lands that meant that a night hour in winter was a lot longer than a day hour. Chaucer, in his Treatise on the Astrolabe (the 14th century’s answer to Asimov’s An Easy Introduction to the Slide Rule) goes into quite some detail on how to figure the natural hours of day and night.

This worked great up until the invention and widespread use of mechanical clocks. Clocks didn’t change the length of the hours from day to day. (If someone asks you what time it is, betcha you say “o’clock” (of the clock) rather than giving the natural hour, dontcha?) Early clocks were only accurate to within a quarter hour. Due to the Equation of Time sundials varied over the course of a year up to around a quarter hour each way. Everything worked out fine.

Every day at meridian passage you’d reset your clock to noon, and let it run for another twenty-four hours, then reset. From meridian passage to meridian passage is one solar day. The clock time varies from the natural time by up to around sixteen minutes (depending on the day of the year). You figure the difference with the Equation of Time.

Look, up in the sky!

It’s a bird! It’s a plane! It’s an analemma!

Yes, this mild-mannered figure-eight of light, strange vistor from the Copernican solar system, is the true sun. If you put a stick in the ground and put a pebble on the tip of that stick’s shadow every day at noon, the pebbles, over the course of a year, would trace out that figure.

One of the mysteries of Chartres Cathedral (proving beyond the shadow of a doubt that it was built by the Templars to hide mystic knowlege) is that at one spot on the floor there’s a brass nail which is only illuminated at noon on Midsummer Day. Was Chartres built just so the light would hit that one spot on just one day? I kinda doubt it. I suspect that what happened is that someone waited until noon on midsummer day, saw where a random spot of light was landing, and banged a nail on in.

Not that the sun following a unique path and shadows casting a unique pattern would be a big secret or much of a surprise by then — the clever buggers who built Stonehenge had the fact that the sun rises and sets at different places on different days, and stands at a different place in the sky at mid-day, figured out.

The true sun is that big yellow thing up in the sky that you can see with your own two eyes if you don’t mind going blind. The mean sun is the average of the true sun over the course of a year. The Mean Sun is what Mean Time is based on, as in Greenwich Mean Time, beloved of navigators everywhere.

The analemma’s shape comes from the fact that the earth’s path around the sun is an elispe, and the axis of the earth is tilted at 23.5 degrees (actually 23 degrees 44 minutes, but who’s counting?) away from the plane of its orbit. By a weird coincidence, the analemma is 23.5 degrees of arc from top to bottom, and is the loops are thirty-two minutes of time (eight minutes of arc) across at their widest.

Local time, setting the clock to noon each day, worked great for centuries. It worked right up to the point people had to start comparing times in different towns. At the same time (so to speak), clocks themselves were moving from crew-served tower-mounted devices to man-portable pocket instruments.

First came the railways. The sun moves across the sky, and it moves pretty fast (about fifteen degrees an hour), but even so railway speeds made the differences in times noticeable.

At my latitude (around 45 North), say there was a train pulled by a John Bull engine, running due west at thirty miles an hour from Appleton to Beeville, thirty miles due west. If that train pulled out of Appleton straight up on noon by the courthouse clock and ran west at 30 MPH it would arrive in Beeville at 12:56 by the Beeville town hall clock. If the same engine running at the same speed left Beeville straight up on noon by the Beeville clock, though, it would arrive in Appleton at 1:04 pm by the Appleton clock. This made scheduling difficult.

If you ever hear the expression “railroad time,” it means the master clock kept by one railroad company or another to which all its conductors’ watches and all its station clocks were set.

The New York Central ran on New York time. The Pennsylvania Railroad ran on Philadelphia time. The B&O ran on Baltimore time. Stations served by more than one railroad had clocks set for several times, including that town’s local time. The situation was … amusing.

Within towns (and cities were growing to the point where the eastern part could be a minute or more ahead of the western edge), setting your watch could be confusing. Individual jewelers would determine the time at their shops and set regulators in their windows. (In case you were wondering what a Regulator was.) Their customers would come by and set their watches to the jeweler’s time. Eventually many towns adopted the Time Ball solution, whereby a ball on a mast on top of the town hall would be lowered at noon town hall time, so folks at a distance could see it all at once and set their watches accordingly. The last remnant of this is seen at New Year’s Eve in Times Square. Other communities rang a bell, blew a whistle, or fired a gun at noon — and you can find examples of those methods still.

The ultimate answer turned out to be time zones — adopted in the UK in 1848, in the USA in 1883, and in Germany in 1894 — in which the earth was divided into twenty-four time zones, each fifteen degrees across, where by common agreement it was the same time at all points inside of that zone. Zone time matched local time only at one meridian in each zone — along the Reference Meridian, mid-way between the zone’s boundaries. The whole country ran on Railroad Time.

Daylight Saving Time is just moving a little farther away from reality, by using the reference meridian for the time zone one zone to the west of your current location to set your clocks. It was introduced in the USA during WWI. I see that President Bush has recently announced the centerpiece of his new energy policy — extending the length of Daylight Saving Time by a couple of weeks. He’s turning the corner in the War on Darkness, I guess.

Sundial Time.

Now is the time to declare loyalty to True Time, based on the True Sun. That time is told with sundials.

First they’ll register sundials, then they confiscate ‘em. When sundials are outlawed only outlaws will have sundials. Support your right to know the true solar time! Make your own sundial.

Shall we tell time by the True Sun? We shall!

Naming the parts: This is your nodus point, which in your case you have not got.

I got your vertical sundials. The style (gnommon) is parallel to the earth’s axis, the dial is vertical.

You wanted to know the declination of your wall, didn’t you? The shape of a vertical sundial’s dial depends on the wall’s declination — noon is always vertical.

This is a calculator for creating your dial, given your latitude and the wall’s declination.

This is why number 12 is always vertical.

I got your horizontal sundials. The style is parallel to the earth’s axis, the dial plate is parallel to the earth’s surface.

I got your equitorial sundials. The style is parallel to the earth’s axis, the dial plate is parallel to the plane of the earth’s equator: The dial has a northern and southern face; the northern face is read in summer, the southern face in winter.

I got your armillary sundials. The style is parallel to the earth’s axis, the dial is parallel to the earth’s circumference.

I got your polar sundials. The dial plate is parallel to the earth’s axis. The style is also parallel to the earth’s axis and the hour lines are parallel to the style and to each other. The distance between the hour lines is not dependent on the latitude but only on the height of the style.

Here’s how to build an analemmic sundial.

A few more dials: A combination sundial and a portable sundial and a pocket sundial.

Some other fun and useful things:

How to find latitude and longitude by Local Apparent Noon.

More on Latitude.

Sundials on the internet.

A Solar Noon calendar.

In conclusion: Sundials. They aren’t just for earth any more.

Comments on Reality Based Time:
#1 ::: Emma ::: (view all by) ::: September 28, 2005, 10:49 AM:

Mr. Macdonald, no offense, but I love you. Madly.

After one of those mornings when one wants to clobber the next human being brave enough to enter one's office with yet another picayune "problem", you serve as a tonic to the intellect.

Thank you.

#2 ::: Steve Eley ::: (view all by) ::: September 28, 2005, 10:57 AM:

This worked great up until the invention and widespread use of mechanical clocks. Clocks didn’t change the length of the hours from day to day.

Actually, I understand the first water clocks did have variable hours.

(There's no reason I can think of that a pendulum or gear clock couldn't use that same cone system to regulate the hours either, but I don't know if any did.)

#3 ::: Andrew Plotkin ::: (view all by) ::: September 28, 2005, 11:00 AM:

What, no mention of the digital sundial?

(Easily findable on Web, but http://www.digitalsundial.com/videos.html
gives you the idea.)

#4 ::: P J Evans ::: (view all by) ::: September 28, 2005, 11:01 AM:

Trains have scheduled times for departure, but they don't leave until the conductor says go, no matter what the clock says. "Conductor Standard Time", anyone?

#5 ::: John Hawkes-Reed ::: (view all by) ::: September 28, 2005, 11:24 AM:

which in your case you have not got

Thank you.

I had this terrible feeling that I was the only one wandering the planet (not that I make a habit of wandering. Perhaps I should.) and having to explain that turn of phrase to the unenlightened. Now I know I'm not alone.

#6 ::: Tom Scudder ::: (view all by) ::: September 28, 2005, 12:09 PM:

All through reading the article, I was thinking of this Hitherby Dragons story:

Each year they made Daylight Savings Time longer, until one day it lasted the whole year round. Then it was spring forward, always spring forward, and never fall back, until noon was where midnight used to be and midnight lost in noon.

In the end it did no good.

The world grew darker, and darker, and darker still.


And much more. It's my favorite Hitherby ever, which is saying a lot.
#7 ::: Niall McAuley ::: (view all by) ::: September 28, 2005, 12:11 PM:

Your newspaper Horoscope column is particularly relevant to the naming Tropic of Capricorn since the Sun is not in fact in Capricorn at the Solstice anymore, it's next door in Sagittarius. No-one has renamed the Tropic or informed the newspaper Astrologers about the precession of the equinoxes in the last couple of thousand years.

Likewise the newspaper column will give Cancer as something like June 22 to July 21, during most of which time the Sun will actually be in Gemini, while at the Solstice itself it will be two houses along in Taurus.

Here's a nice analemma picture from Delphi.

#8 ::: Christopher Davis ::: (view all by) ::: September 28, 2005, 12:32 PM:

They still do a daily ball drop at Royal Observatory Greenwich, but at 1pm instead of noon.

#9 ::: Michelle ::: (view all by) ::: September 28, 2005, 12:58 PM:

That's it.

We have too much time on our hands.

#10 ::: protected static ::: (view all by) ::: September 28, 2005, 01:12 PM:

'crew-served tower-mounted' <snort />

Michelle: if you used a sundial, you would no longer have too many hands on your time... (assuming you swing analog, of course)

#11 ::: Bruce Adelsohn ::: (view all by) ::: September 28, 2005, 01:30 PM:

Thank you for the sundial links. There are a couple there that I hadn't already bookmarked.

But I have never seen a good noncircular definition of time, per se. Maybe one of these days (as it were :-)

#12 ::: Laura Roberts ::: (view all by) ::: September 28, 2005, 01:37 PM:

The Yin-Yang symbol is another depiction of the yearly solar cycle.

I once read a book called Runic Astrology by Nigel Pennick. His rants about the evilness of time zones and Daylight Savings Time were something to behold. He was all about Local Apparent Noon.

#13 ::: Xopher (Christopher Hatton) ::: (view all by) ::: September 28, 2005, 01:58 PM:

The sun is overhead somewhere on the Tropic of Capricorn at the moment the sun enters the traditional astrological sign of Capricorn, which moment is the Summer Solstice. It may be in the sidereal Sagg, but that doesn't help any schoolchildren understand anything. I'd leave that for highschool.

Interestingly, that means there are only two latitudes (the tropics) on Earth where the sun is directly overhead exactly once during the year. All other latitudes get two (between the tropics) or none (outside the tropics). But of course they move around from year to year, longitudinally-wise-speaking, as my favorite radio personality would put it.

It would be interesting to map the places where the sun is directly overhead (i.e. the point where LAN coincides with the Solstice on a tropic, and interpolated for LAN corresponding to the appropriate declinations elsewhere). My instinct says it would be a big sinusoidal curve, not phasing with its overlap (since the solstices and equinoxes vary quite a bit by time of day). But I don't know, and the calculations are beyond my abilities at this time.

Another exercise to baffle the mind: for a given point between the tropics, how long is it between times when the sun is directly overhead? Make reasonable assumptions about the size of a "point" and degrees to use for the orb of noon.

#14 ::: Jeremy Osner ::: (view all by) ::: September 28, 2005, 01:59 PM:

Tom Scudder -- thanks for the HD pointer. For some reason I do much better with Hitherby Dragons when somebody directs me there, than when I try to sally forth on my own. That is a great story, and a fine prelude as well. Particularly I like the use of "immine" verb.

#15 ::: Dave Bell ::: (view all by) ::: September 28, 2005, 02:04 PM:

In Hong Kong they strike a gong, and fire off a noonday gun.

#16 ::: Xopher (Christopher Hatton) ::: (view all by) ::: September 28, 2005, 02:04 PM:

Whoops. It's gonna be different for every latitude, isn't it? OK, just do the equator. Note that the sun is directly overhead somewhere every equinox (i.e. twice a solar year), but only the place where LAN corresponds to the actual moment of the equinox actually gets a direct overhead hit.

#17 ::: Mac ::: (view all by) ::: September 28, 2005, 02:12 PM:

Ti-i-i-ime
is on my side...
(yes, it is)
ti-i-i-ime
is on my side...

What do you suppose all this means in terms of those of us who don't wear a watch?

#18 ::: Larry Brennan ::: (view all by) ::: September 28, 2005, 02:33 PM:

OK, I'm down for True Sun time. Now, what's the best way to stick a sundial and compass to my PDA? And is there an extension for Outlook and Exchange Server?

#19 ::: Echidna ::: (view all by) ::: September 28, 2005, 02:58 PM:

The world will soon take another step away from True Time, with the upcoming elimination of the Leap Second. (The primary need for leap seconds is not, as is generally supposed, due to the progressive lengthening of the day from one year to the next, but due to the accumulated lengthening of the day between 1820 -- when the length of the day was officially defined -- and the present. Leap seconds are generally needed about every 18 months, though there hasn't been one for seven years.)

This will mean that civil time will begin to drift away from solar time; given long enough, the sun would rise at midnight. It will take about 600 years for the difference to reach an hour.

(The dire consequences are outlined at http://www.ucolick.org/~sla/leapsecs/dutc.html )

Of particular interest to me as an astronomer would be the failure of telescope pointing systems between 2025 and 2027 (depending on the value chosen for the deceleration of the Earth); of particular interest to this thread would be the "failure" of analemmatic sundials (being off by more than 2 minutes) between 2083 and 2116.

Absent new adjustments such as a leap hour, noon would become midnight by 5033.

We recently heard a talk on this issue in the astronomy department; it was the opinion of the man giving the talk that there's nothing we could do about it, as the decision was being made by shadowy committees somewhere and well-funded telecommunications firms were backing the change.

(I note in passing that the Director of Time, at the US Naval Observatory, has the coolest job title in the world.)

#20 ::: Jonathan Lennox ::: (view all by) ::: September 28, 2005, 03:32 PM:

Echidna: I wouldn't be so definitive about "the upcoming elimination of the Leap Second." The US has proposed this to the ITU, but it doesn't sound like anyone else likes the idea.

http://news.bbc.co.uk/1/hi/sci/tech/4271810.stm describes the British opposition.

#21 ::: Terry Karney ::: (view all by) ::: September 28, 2005, 04:02 PM:

Just a nit, to pick: It's Daylight Saving Time.

Other than that, I hooted (and "which in your case you have not got", among other places).

TK

#22 ::: Jeremy Osner ::: (view all by) ::: September 28, 2005, 04:02 PM:

In Hong Kong they strike a gong, and fire off a noonday gun.

I was reminded just now by the television mounted to the wall behind my desk, that on the floor of the New York Stock Exchange, they ring a loud bell every day at 4 o'clock. Perhaps to allow the traders to set their watches.

#23 ::: Clifton Royston ::: (view all by) ::: September 28, 2005, 04:26 PM:

Did Indiana decide to buckle on DST this year? Are Arizona and Hawaii the only US hold-outs? (We get plenny daylight, no need save.)

Dating myself here: Does anybody else remember the Feiffer cartoon on Nixon's DST extension during the early '70s energy worries? "Today we're going to show you how to keep warmer in winter by cutting a foot off one end of your blankets... and sewing it onto the other end. We call this Daylight Savings Time!"

#24 ::: TH ::: (view all by) ::: September 28, 2005, 04:50 PM:

Ball drops? Flags? Don't you have church bells on your side of the water? Her (at least in .de and .at) the church bell will sound the full count of the hour every daylight hour and one to four strikes of a different bell for every quarter of an hour.

And more exact than the quarter of an hour no human needs to know the time. All those minutes and seconds are just overexactitude which hinders rather than helps.

(And thanks for reminding me that I need a sundial on the house.)

#25 ::: hrc ::: (view all by) ::: September 28, 2005, 04:55 PM:

This simply reminded me of my favorite KY joke (which I as a northerner am no good at telling--be forwarned), where the city slicker watches the farmer take his herd of pigs one at a time to water at the trough. And after an hour has passed, asks the farmer why he does it that way, since it takes so long. The farmer replies, "Whay? whut's tahm to uh hawg?"

anyway, it loses a lot in the translation, but in the right hands/mouth it is a very good KY story.

#26 ::: James D. Macdonald ::: (view all by) ::: September 28, 2005, 05:07 PM:

Indeed we do have church bells in the USA, but not so many toll the hours that I've noticed.

Here, for your amusement, is a picture of the Time Ball in the port of Hamburg: http://www.fremo.org/betrieb/images/timeball.jpg

#27 ::: Simone ::: (view all by) ::: September 28, 2005, 06:20 PM:

Ah, analemma, you sexy thing you. We have a bit of our Prototype 1 of The Clock of The Long Now that corrects the clock's time by using 10,000 years worth of analemmas stacked on top of each other...we call it the
Equation of Time Cam

#28 ::: Lois Fundis ::: (view all by) ::: September 28, 2005, 06:48 PM:

Chaucer, in his Treatise on the Astrolabe (the 14th century’s answer to Asimov’s An Easy Introduction to the Slide Rule)

What's an example of famous authors playing Jeopardy!?

#29 ::: Lois Fundis ::: (view all by) ::: September 28, 2005, 07:34 PM:

The analemma on Mars looks like an egg rather than an 8; I guess this is due to Mars' axis being not as tilted.

Chartres dates back way before the Templars or the "modern" Gothic cathedral; its religious significance goes back to the Druids, who seem to have worshipped there before Julius Caesar came, saw, and conquered.

My dad, who worked for the Pennsylvania Railroad, would refer to "railroad time" as late as the 1960s. Though standard time had been in force for several decades by then, "railroad time" in Dad's day was more in reference to daylight savings time, or the lack of it: back then some communities started and stopped observing daylight on different dates than others, or not at all, and not just Indiana either. Dad had to keep the time the railroad did, which I believe was as you say, Philadelphia time.

As for the three ornery states: Hawaii doesn't need daylight time as much, because in the tropics the difference in the lengths of days and nights are much less. In Honolulu, for example, sunrise on June 21 is 5:50 a.m. and sunset 7:16 p.m., less than an hour and a half, compared with, say, Boston's 5:08 and 8:25, more than three hours (I adjusted the Boston times to Daylight Time). Arizona is (a) conservative as all heck and (b) far enough south that they can get away with it. And Indiana is a case unto itself. For one thing, some parts of the state feel they're in the wrong time zone. (I love the fine distinction in this line from the Wikipedia article: "Technically, during the summer months, this meant most of Indiana was on Eastern Standard Time, but functionally most of the state was on Central Daylight Time.") But yes, they are pretty much "buckling in" on DST as of next year.

Terry, as for your nit, officially you're right, but everyone says "daylight savings" anyways. :-)

#30 ::: Lois Fundis ::: (view all by) ::: September 28, 2005, 07:36 PM:

Mars' axis being not as tilted.

Footnote: I wanted to say "being not as bold as love", then cross out "bold as love" and add "tilted," but couldn't get a strikethrough to show.

#31 ::: Terry Karney ::: (view all by) ::: September 28, 2005, 08:50 PM:

Lois: Not everyone. Me, and the AP, and a few other people with that particular quirk.

I know most people say savings, but (as with the adverb) I shall fight a rear-guard action to defend it.

Everybody needs a windmill.

#32 ::: Maureen M McCarty ::: (view all by) ::: September 28, 2005, 09:47 PM:

I read through the piece wondering when someone was going to mention Indiana and our sorry state of time. Yes, despite our numerous woes (not enough $$ for schools, parks, and police / fire services), we had to spend much time, money and angst haggling over whether or not to jump on the DST bandwagon. That deed done, the haggling is now about whether we're Eastern or Central time. Whatever is picked, several counties want the other option so we'll never all be on one time and it will still be confusing. Despite the decision, I will not be springing forward of falling back. I think it's a crock and decided to align myself with True Time months ago. For scheduling purposes, the time is whatever the cellphone says it is, since it already keeps track better than I do.

#33 ::: Larry Brennan ::: (view all by) ::: September 28, 2005, 09:52 PM:

Maureen - As you drive from micro time zone to micro time zone in IN, does your cellphone adjust?

Or - what time zone would Verizon use (WTZWVU?)

#34 ::: Martin Schafer ::: (view all by) ::: September 28, 2005, 10:10 PM:

Another arcane bit in keeping with this thread. The term widdershins, which is usually defined as counter clockwise, is actually the opposite of deosil, which means the direction the sun moves across the sky. So in the southern hemisphere widdershins should be clockwise and in the tropics it should vary based on time of year.

#35 ::: Maureen M McCarty ::: (view all by) ::: September 28, 2005, 10:37 PM:

Larry - I believe it does. I've only noticed when going south toward Louisville... it changes a bit before I get to the state line. I've never checked going toward Chicago since it takes all my concentration to not get run over by traffic. And it *is* Verizon :-)

#36 ::: pericat ::: (view all by) ::: September 29, 2005, 02:10 AM:

Every day at noon in Vancouver, the harbour whistle blows the first four notes of "Oh, Canada", causing a virulent outbreak of earworms in all within hearing range. Luckily, this lasts only a couple of hours or so. And every evening, they shoot off the nine o'clock gun in Stanley Park. This, as I understand it, means it's bedtime in Victoria and we need to keep the noise down.

#37 ::: Danny Yee ::: (view all by) ::: September 29, 2005, 02:28 AM:

Now we have GPSes and suchlike, I think we can get rid of time zones and go back to continuous timezones.

#38 ::: Epacris ::: (view all by) ::: September 29, 2005, 03:24 AM:

Martin, there was a bit of discussion of widdershins, deosil & sundials in the Busted (September 21, 2005) comments, if'n you're interested in the subject.

#39 ::: jotter ::: (view all by) ::: September 29, 2005, 03:42 AM:

Ah analemma. The word I strive to remember as the days draw down to the solstice, but perhaps it won't be so hard this year thanks to your equinoctial reminder. Didn't most people first see it on a globe, where it appears between the two tropics, somewhere in the Pacific Ocean? You don't mention that pebbles on a stick analemmas constructed at different locations are not quite the same shape; I've often thought this one of the charms of the figure. Finally, the analemma appears whenever the sun is around, not just at noon. Try plotting the time of sunrise vs the time of sunset over the course of the year. I enjoyed your piece very much. Thanks.

#40 ::: Epacris ::: (view all by) ::: September 29, 2005, 03:58 AM:

Plans for Sydney Observatory began as a simple time-ball tower (Sydney Observatory timeball - J.Sarkissian) on the top of the highest nearby hill, near the existing signal station, but it was soon agreed to expand the tower into a full observatory. The Observatory is now part of the Powerhouse Museum, and hosts many public astronomical events.

For navigation, ships want their timepieces as accurate as possible. The astronomers had several important observations to make at noon, so every day at exactly 1.00pm, the time ball on top of the tower would drop to signal the correct time to the city and harbour below. At the same time a cannon at Fort Denison (on Pinchgut Island) was fired. Although the cannon no longer fires, the ball drop continues (I think).

The rather sad story of the Sydney southern star catalogue: David King and Nick Lomb, Proceedings of the Royal Society of New South Wales (Vol 116, p 53).

#41 ::: John M. Ford ::: (view all by) ::: September 29, 2005, 04:28 AM:

Now we have GPSes and suchlike, I think we can get rid of time zones and go back to continuous timezones.

Should I assume you're joking?

On the chance that you're not, this is a nonviable idea. Understand a basic principle of time: the only times that matter to you, as an individual, are when things happen and how long has elapsed/is remaining until those instants.

Understand that we never had "continuous time zones." We had places setting the town clock by an approximation of local solar noon, and waiting for it to gain or lose enough to be noticeable.* Towns that might have been exactly a solar hour apart might, in terms of local time, be anywhere from thirty to ninety minutes -- probably some odd number in between. Standard time was created not because the town clock didn't serve the town adequately, but because commerce and communication required that you know, exactly, what time it was down the line.

With the system we have, everyone has the same minute count (with the very few exceptions of 30-minute subzones, which are frankly more a local notion of solar propriety than something necessitated by the system). There are now twenty-four discrete hour differences, but those are (relatively) easy to correct for, and more importantly, they are fixed. Constantly "correcting" one's watch for local solar time would mean, in the temperate zones, moving by about a minute every time one went ten miles east or west. (It would vary by latitude, which makes it worse.) In other words, it would be impossible to compare watches with anyone who wasn't exactly on your meridian, and as you drove east or west trying to get to an appointment, your timepiece would slip backward or forward. To arrive on time, you'd have to know the time differential to the nearest minute, and set an elapsed-time side counter to figure out how close you were to making it.

In short, nobody would have any useful knowledge of what time it was. This may be swell if you're a particle and Werner Heisenberg is looking for you, but it's not much good for human society. If you actually wanted to simplify matters and be "futuristic," have everyone, everywhere, keep GMT and accept that local sunrise might come at 1800. Those of us who are already dissasociated from the day-night cycle wouldn't care. Just remember that you're still going to need an International Date Line somewhere.

*The old story of The Caliph's Clock is applicable here.

#42 ::: Niall McAuley ::: (view all by) ::: September 29, 2005, 05:59 AM:

I think we can note that the tropics are named for the Zodiacal signs for historical reasons without fudging the fact of whereabouts in the sky the Sun is.

Precession is cool. You can demonstrate it with a top or gyroscope, and the idea that the whole Earth is doing that wobble every 26,000 years is also cool.

There's a star map of the Northern Precession Circle here.

#43 ::: Teresa Nielsen Hayden ::: (view all by) ::: September 29, 2005, 08:04 AM:

Mike, I don't know that story. Tell me about the Caliph's clock.

#44 ::: Jo Walton ::: (view all by) ::: September 29, 2005, 08:13 AM:

What would be wrong with everyone keeping GMT, and just calling the time they get up 12h00 and the time they go to bed 03h00? It doesn't matter what names you give the hours, any more than it matters that September isn't autumn in Australia.

#45 ::: Patrick Connors ::: (view all by) ::: September 29, 2005, 08:49 AM:

Lois Fundis:

I don't know about famous authors, but Rick Cook won a decent year's income on Jeopardy some years back.

#46 ::: Dan Guy ::: (view all by) ::: September 29, 2005, 09:22 AM:

I prefer my time of day in powers of 10, and so have become enamoured of internet time, though I'm not pleased that Swatch decided to pull another meridian into the pot.

#47 ::: Michael ::: (view all by) ::: September 29, 2005, 10:42 AM:

As a resident of the aforementioned tropics, let me correct you on one point: they're hot, yes, but not a nasty place to live. I'm working on WiFi poolside and it's the end of September. And I'll be doing the same thing in January. Seriously. No going back.

#48 ::: Lori Coulson ::: (view all by) ::: September 29, 2005, 11:20 AM:

At Ohio State University, the carrillon (sp?) oh, hell, bell tower in Orton Hall chimes the hours and quarters.

It also is played for about a half hour every day, at 11:45 am and 3:45 pm. Since it doesn't have a full keyboard of chimes this can produce some interesting renderings of songs...

It can be heard for some distance. When I lived within a mile of campus you could hear it striking the hours and quarters during the quieter hours of the night.


Lori

#49 ::: rhandir ::: (view all by) ::: September 29, 2005, 01:20 PM:

re: the Caliph's clock
Can be found in this Dick and Jane collection, according to this page.

A quick google search for the phrase turns up little else, excepting references to a story called the Caliph's son, and some flakey erotica.

Having never read it, I am wicked-curious, Mr. Ford, do enlighten!
-R

#50 ::: Lois Fundis ::: (view all by) ::: September 29, 2005, 01:31 PM:

Patrick Connors:

OK, but I was referring to the idea of Chaucer answering Asimov, when he lived 300 years before. Thus Jeopardy, where the answer comes before the question.

#51 ::: Peter ::: (view all by) ::: September 29, 2005, 02:55 PM:

Getting back to science fiction, the international date line (or rather, the lack of it, since both of these works were written before it existed) has figured prominently in two SF-related works that I know of. The more obscure one is Lewis Carroll's A tangled tale, and the dateline seems to have had Carroll completely baffled. It's online here; see knot 10, the middle part: "change of day," starting with

“It changes from Wednesday to Thursday at midnight, doesn’t it?” Hugh had begun.

“Sometimes,” said Balbus cautiously.

“Always,” said Lambert decisively.

“Sometimes,” Balbus gently insisted. “Six midnights out of seven, it changes to some other name.”

The less obscure one, of course, is "Around the World in Eighty Days," by Verne, which was written earlier.

#52 ::: Therese Norén ::: (view all by) ::: September 29, 2005, 03:16 PM:

Railway time was the introduction of a standard time in Sweden, and it was decided to be Gothenburg time, since it's on the west coast.

Meaning that people on Stockholm time would be early for their trains, instead of the Gothenburgers missing theirs.

#53 ::: Emily H. ::: (view all by) ::: September 29, 2005, 04:40 PM:

The Bell Tower at UNC-Chapel Hill (about a tenth of a mile from my current location, as it happens) rings out the quarter-hours to the melody of the Brownie closing: "Oh Lord our God/Thy children call/Grant us thy peace/And bless us all." 1st line at x:15, first 2 lines at x:30, and so on.

I revised my judgement of this from "annoying" to "convenient" when I lost my watch last week; it means I don't need to find a clock as long as I know the time within an hour.

#54 ::: John M. Ford ::: (view all by) ::: September 29, 2005, 05:15 PM:

Curiously enough, I first read "The Caliph's Clock" in an old school reader I had when I was little. (No, littler than that.) I don't think it cah have been People and Progress, since mine was definitely not written on a "Dick and Jane" level. As you can probably guess, I wouldn't have read it, at least more than once, if it had been. The story list doesn't sound right, either -- I certainly read "Ben and Me," but it was Robert Lawson's version. My book also had a yarn about visiting General Cash-My-Check and the Dragon Lady of Long Island at Christmas during the war, which may charitably be said to be an artifact of its era. I would imagine that the Clock mentioned the same story, perhaps rewritten by the publisher for a different school reader haunted by the werblings of Baby Sally.

Maudlin Reminiscence Theater over, I know the story has broader provenance -- a Google brought up a mention that someone's doing it as a student opera -- but it seems to be rarer than I'd thought.

Anyway: A Caliph, who is fascinated by new things, and his Vizier, who for the first time in such tales is not a scheming bastard, accept the visit of a Yankee Peddler, who sells the Caliph a fine chiming clock. The Caliph installs it on a marble pedestal in his garden, and decrees that from now on, the clock's time is the official time of the country, and none other is to be followed for any purpose public or private. (Issues of prayer are not mentioned.)

The clock, as you might guess, begins to go off, and gradually the daily cycle of the country slips out of sync with the Sun. "When all the world was as black as your hat, the Caliph and the Vizier were watering the plants in the garden." The Vizier tries politely to point out that something must be wrong, somewhere, but the Caliph refuses to believe that an object of such fine manufacture can be in error.

Finally, one night, the clock winds up to strike as usual, but instead it gives a great, rending metallic BONG and stops still. This wakes the Caliph, so to speak, and without any fuss the clock becomes a garden ornament, and the country returns to its usual cycle.

There probably should be an expression for the assumption that a story one knows very well from childhood must also be known by everybody (at least, everybody of a broadly similar ethnosocial background). Nonisoapheisis? Suitably unintelligible, but not even very good as a first approximation.

#55 ::: Marilee ::: (view all by) ::: September 29, 2005, 06:06 PM:

My favorite time picture.

#57 ::: CHip ::: (view all by) ::: September 29, 2005, 11:03 PM:

Peter -- there's also a short story (which I thought I could lay hands on, but my library has come up empty) in which, for no obvious reason, the line runs through the capital city of an Earth-settled Mars; a thief from one side of the city plans a leisurely weekend looting a museum, not thinking that it's on the other side of the city and therefore not yet into the weekend.

#58 ::: David Goldfarb ::: (view all by) ::: September 30, 2005, 04:28 AM:

That's "The Martian Crown Jewels", by Poul Anderson.

#59 ::: Oskar ::: (view all by) ::: September 30, 2005, 01:14 PM:

What I now need is a utility into which I can enter my home coordinates, and which will then continuously update my computer clock to actual local time.

Any programmers out there?

#60 ::: Patrick Connors ::: (view all by) ::: September 30, 2005, 02:39 PM:

Lois:

(re: the notion of Chaucer citing Asimov)

Far too subtle for me this week.

And time travel makes my head spin in charming strange directions at the best of, er, moments.

#61 ::: Lois Fundis ::: (view all by) ::: September 30, 2005, 04:38 PM:

Oh, and by the way, my math fu must really be off this week. I meant Chaucer lived 600 years before Asimov, not 300.

#62 ::: abi ::: (view all by) ::: September 30, 2005, 05:37 PM:

Quoth Epacris:

The astronomers had several important observations to make at noon, so every day at exactly 1.00pm, the time ball on top of the tower would drop to signal the correct time to the city and harbour below.

That's a better explanation than the one they give at Edinburgh Castle. The ball drop at the observatory on Calton Hill across the way used to trigger the One O'Clock Gun. (It's now triggered by a wee man with a watch.) Why not noon, ask tourists on the official tour.

"Well," say the guides, "if we fired it off at noon we'd have to shoot off twelve shots. But we Scots, we're more careful wi' our money than that..."

This message is officially cleansed of all Questionable Content.

#63 ::: Kate Yule ::: (view all by) ::: September 30, 2005, 06:47 PM:

And every evening, they shoot off the nine o'clock gun in Stanley Park. This, as I understand it, means it's bedtime in Victoria and we need to keep the noise down.

Love it.

Circa 1970 in my Pittsburgh suburb, the volunteer fire station down the hill let off their siren nightly at 6:00. It was a good bet that any household with kids had dinner at ten or fifteen minutes past 6.

One sentence from a long-ago article in Smithsonian has stuck with me for years. It asserted that "There was no such thing as 7:02 until the invention of the railway timetable." Some truth to that.

#64 ::: CHip ::: (view all by) ::: September 30, 2005, 10:56 PM:

David Goldfarb: uh, not that I see; that's what I thought it was from the location (Boucher) my mind tied to the plot, but I found not (and just reread in detail to be sure). The action is mostly on Phobos and does not involve a museum.

#65 ::: Tom Scudder ::: (view all by) ::: October 01, 2005, 01:49 PM:

The date line story, I think I remember being by Arthur C. Clarke. I have no idea of title or where it might be collected.

Another sort-of-science-fictional story wherein the International Date Line comes into play is THE ISLAND OF THE DAY BEFORE by Umberto Eco (technically, a historical, I guess, or "literature", but I at least find Eco's discursions pleasing to my sensawunda), wherein the protagonist is stranded on an abandoned ship moored within eyesight of an island, yet (by his calculations) on the other side of the Date Line. This is a source of considerable philosophical anguish to him.

#66 ::: Diana ::: (view all by) ::: October 07, 2005, 10:26 PM:

My very minor contribution, as to why the day has twelve hours, the hours sixty minutes, the minutes sixty seconds:

The Summarians/Babylonians used base 12 as their numbering system, instead of base 10 as we do (it works quite well until you start serious multiplication & devision). They also had quite an elaborate calendar, and divided the day into twelve hours (because they divded everything into twelve) and then the hours into sixty minutes.

The Greeks and the Romans inherited the hours and the "lore" about the minutes and seconds, but without clocks or a religion that hung on the calendar, didn't really keep much track of them. The Romans at least were quite comfortable with the idea that hours could change their actual time -- summer day hours were longer than winter hours, and winter night hours were longer in winter.

Medieval alchemists, in their attempts to regain the ancient wisdom of the Chaldeans, timed their experiments in turning lead into gold by "Chaldean time": 12 hours in a day, sixty minutes in an hour, sixty seconds in a minute. This established the idea that an hour was a standard length of time, unlike a day, and as part of their equipment they created elaborate clocks. Since alchemy was at least partly a hobby of the rich, the clocks got pretty fancy.

Next thing you know, clocks with twelve hours, sixty minutes, sixty seconds were toys of the wealthy, to be displayed upon the marble mantle of your chateau.

And thus modern time was born.

Alas I haven't a cite for this. But this is a pretty literate crowd -- check your medieval history of the alchemists, that's where it should be.

#67 ::: David Goldfarb sees comment spam ::: (view all by) ::: October 22, 2005, 08:16 PM:

but with none of the links working (except perhaps the one in the name field)

#68 ::: Benjamin Wolfe ::: (view all by) ::: July 19, 2011, 08:27 PM:

What if time is just an artifact of perception? (credit for that line goes to Kage Baker, whose wonderful work I only discovered after she passed).

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