A brief history of time

Stanley - Thursday

I have always been fascinated by time, from its measurement, to our perception of it, to its impact on our lives.

Most of the world today uses the Gregorian calendar for civil purposes, even though the motivation behind the establishment of the calendar was religious. It was made the official calendar of the Catholic Church in 1582, and named after Pope Gregory XIII. It took hundreds of years for its widespread adoption, partly because Protestants thought it was a nasty Catholic plot to bring them back into the fold. Greece, for instance, only adopted it in 1923, while Turkey waited another three years.

 The measurement of a day has obvious origins. It is the time it takes the earth to rotate once about its axis. 

A year is the time for the earth to orbit the sun. And that year is divided into 365 days. Of course, we know now that it actually takes the earth 365.25 days to go around the sun, which has caused some problems historically, which were solved by adding a day to February every four years, giving us the leap year. 

Well, actually the orbit time is actuallynot 365.25 days but 365.2421891 days, which caused more problems because it is a little less than 365.25 days. That makes the four-yearly adjustment not work over the long haul. The smart men who developed the Gregorian calendar (for the most part two Italians,  Aloysius Lilius (known as Lilio) and Christopher Clavius) realised this and added another wrinkle to take care of it. In years ending with 00 (such as 1900, 2000), there would be no leap year unless the year was divisible by 400 (eg. 1600, 2000). So there are plenty of people alive today who will have to remember NOT to add a day to February 2100.

Lilio

.Have you ever wondered why September, October, November, and December are so named? The names are odd since the roots of these months are seven, eight, nine, and ten -- certainly not the position of the months in the calendar.

Well, the Gregorian calendar is based on the Julian calendar, which was introduced by Julius Caesar in 48 BC. It had months of 30 or 31 days, except for February, which had 29 days and an extra day every four years.

The Julian calendar was based on an earlier Roman calendar established in 452 BC, which in turn was based on a calendar established by Nuna in about 700 BC.  That's a long time ago. His calendar was based on one established in 738 BC, which had only ten months, named Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, and December.Notice the fifth through the tenth months were based on the numbers five through ten. The problem with this original calendar is that it left out about 60 days of the year. Nuna's scientists realised this and added two months to rectify the situation - adding January at the beginning of the year and February at the end of the year. So, the months became Januarius, Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, December, and Februarius.

For reasons I don't know, the 452 BC calendar moved Februarius to be after Januarius, which left the number-based months out of sequence. To muddle things a little more, modest Julius changed what had been the fifth month, Quintilis, to be named after himself - Julius. 

Julius Caesar

Of course, Emperor Augustus wasn't to be outdone, so he renamed Sixtilis after himself. He also moved the 29th day in February to Augustus, so as to have the same number of days as Julius.

Augustus Caesar

You can't make this up.

So, years and days are based on naturally occurring phenomena. But what about months? It is easy to see why people used the moon as the basis for a month. After all, it rotates around the earth in a regular orbit of 29.53059days. In fact, some calendars still use this as their basis. The obvious problem with using a lunar month is that its duration doesn't fit neatly into a year, so early astronomers decided to use varying numbers of days as the basis for months rather than lunar cycles.

What about hours and seconds? Why 24 hours in a day? Why 60 minutes in an hour and 60 seconds in a minute?

Well, again we have to go back a long way in time.

Today, we use the decimal (or base 10) number system. It's convenient because we have ten fingers. However, the duodecimal (base 12) system was widely used for thousands of years in different parts of the world. It is also convenient - our four fingers have three joints each, allowing the thumb to count to twelve. Twelve is also divisible by more numbers than ten - 2, 3, 4, 6 versus 2 and 5.

About three and a half thousand years ago, the Egyptians used a sundial and divided the time between sunrise and sunset into twelve parts because they used the duodecimal system. One obvious problem with this is that the twelve divisions were of different lengths at different times of the year. Think twelve parts between sunrise and sunset in Iceland in summer versus winter.

Keeping track of times at night was obviously very difficult. The Egyptians figured out how to use twelve stars moving across the sky to accomplish this. They also developed a water clock that compensated for decreasing water pressure. It too was divided into twelve parts.  So, with daylight divided into twelve parts and night the same, there was the basis for the twenty-four hour day.

Greek water clock, 500 BC

It took over a thousand years before making all the hours the same length was proposed. It was Greek astronomers, like Hipparcus in about 150 BC, who started doing their astronomical calculations with twenty-four theoretically equal hours. The length of these hours was one-twelfth of daylight on the equinox.

So where do minutes and seconds come from. Again, we go back to Greeks like Hipparcus, who based their ideas on a sexagesimal (base 60) number system developed around 2000 BC by the Sumerians, and adopted for general use by the Babalonians. Base-60 arithmetic has the advantage that 60 is divisible by 2, 3, 4, 5, 6, 10, 12, 15, 30, and 30.

Hipparcus developed the idea of there being 360 equally spaced lines of latitude and 360 lines of longtitude (multiples of 60), equally spaced at any latitude. In his treatise Almagest (about A.D. 150), Claudius Ptolemy expanded on Hipparchus' work by subdividing each of the 360 degrees of latitude and longitude into smaller segments. Each degree was divided into 60 parts, each of which was again subdivided into 60 smaller parts. The first division, partes minutae primae, or first minute, became known simply as the "minute." The second segmentation, partes minutae secundae, or "second minute," became known as the second.

However, you will immediately notice that there are 360 degrees of latitude, or 360x60 = 21600 minutes. In our time system, there are 24 x 60 = 1440 minutes. So, there is no equivalence. It was only in the 13th Century that the notion of dividing the hour into 60 minutes and each minute into 60 seconds came about - again using the sexagesimal system. The same words used for measuring latitude and longitude were used. 

It was only when mechanical clocks became available several centuries later that ordinary people started paying attention to hours and minutes. To this day, most clocks don't show seconds.

Of course, today a second is not defined as 1/86400th of a mean solar day, but rather in an even more accurate way. In 1997, the following definition was internationally agreed to:

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. 

Gasp.

Needless to say, minutes and second also don't fit exactly into a day, so there are also leap seconds. Eight times a decade there are minutes with 61 seconds.

The way we keep track of time has always seemed a bit crazy to me at various levels.

First, the idea of ante meridiem (a.m.) or before midday, and post meridiem (p.m.) or after midday is very inefficient. When writing or talking about time, one often has to qualify the time by a.m. or p.m., unless the context makes it clear. 

It can also be confusing, as I recently found out. I booked an airline ticket from Minneapolis to Las Vegas, leaving at 2:30 pm and returning at 12:45 pm. Or so I thought. Yesterday, in checking my ticket, I noticed that I had inadvertently booked the return for 12:45 am. If we used the much more sensible 24-hour clock, I would have noticed this immediately because the departure times would have been 1430 and 0045.

Even some people who use the 24-hour clock put a colon between hours and minutes, such as 14:45. Since there can be no ambiguity about 1445, the colon is redundant.

One of the outcomes of the French Revolution was the introduction of the metric system, which brought sanity to the world of weights and measures, even though in some places its adoption was slow. In the cases of Myanmar and the United States, as well as Liberia, adoption has never taken place. The proponents of the metric system also proposed changing the measurement of time. The thought it made sense for the day to have 10 hours, each divided into 100 minutes, divided into 100 seconds. As you know, that didn't go anywhere.

There is one other aspect of time that is controversial, namely Daylight Savings - the practice of shifting the clock forwards or backwards by an hour to accommodate the seasons' different length days. Right now, there are proposals to scrap the idea completely.

Another proposal, which I like a lot, but won't go anywhere, is the idea that everywhere on the planet should be at the same time. So, 7pm or 1900 in Minneapolis would be 7pm or 1900 in Glasgow, and 7pm or 1900 in Johannesburg, and 7pm or 1900 in Auckland. Why do I like this idea? Because it rids us of the need to deal with time zones when talking about time. 

The other thing that fascinates me about time is our perception of it. Why is it that sometimes time flies and sometimes it drags? I remember in August 1963, I was sitting in a history class, bored out of my mind as we revised for our end-of-year matriculation three months away. Every few minutes I would look at my watch. Time dragged, and time dragged. And time dragged. So, I took off my watch hoping to speed up the passage of time. It worked, and I never wore a watch again, except when I was being a pilot.

I can remember impatience when young waiting for Saturday to arrive to go out on a date. I remember, too, time flying as an exam loomed for which I was ill prepared. 

As I get older, time seems to pass faster and faster - which is sad as there are so many things I still I want to do. 

There one other aspect of time that seems important. One of the things that has an impact on visitors to the United States is how so many people believe that the more hours they work, the more productive they are. They often feel that their worth is tied to how long they're at their desks. And how little vacation they take. This adds a psychological pressure that has to be unhealthy. This is probably tied to the often-stated regret expressed by people approaching death that they hadn't spent more time with their families or friends.

Finally, I'd be interested in hearing from readers what their perceptions are of time, its passage, and impact. Please do that if you have the time.