Sundial Time, Local Time, Standard Time: What’s the difference?

The mission of the TimeNavigators website is to introduce young people to the nature of time … how it feels as it goes by and how we mark it, measure it and tell each other what time it is. The vocabulary of time started in pre-history, but we moderns have managed to put our own spin on some of the concepts.

In the beginning, time reckoning was tightly connected to astronomy.

The motions of the sun & stars connected us with the passage of the hours during the day & night. The moon and seasons connected us to longer cycles of time, like weeks, months and years.

With TimeNavigators’s clock dials and calendars, our kids can begin to learn the vocabulary of time and begin to develop a sense for how time feels as it passes.

Before sundials and clocks came along, one way to reference time was to talk about where the sun was, is or will be in the sky. Examples of this are:

  • We left at sunrise.
  • It’s high noon now. Let’s eat.
  • We’ll stop the hunt at sundown.
  • Let’s meet at the fork in the north trail tomorrow afternoon, when the sun is three-hands above the horizon.

Pre-clock people lived in a world where they spent much more time outdoors than most modern people do. In those days, most were involved in agriculture, which is largely an outdoor activity. Because artificial lighting was expensive and poor in quality, even homemakers and craftspeople did as much of their work outdoors as possible. Pre-clock people became very good at tracking where the sun was (or should be on cloudy days). Just as you can look at your watch today to see if it’s getting late, they could watch the sky and get a feeling for how fast the day was passing.

So how were times referenced?

Early on, the pre-clock marking of time was fairly unstructured. One could use a hand gesture to indicate how high the sun should be at the beginning of some event. [See blog post “Drilling Wells and Telling Time in Niger” for a modern story about this.] Or sun positions could be quantified with a simple counting system like “two hands above the horizon,” or by using simple descriptors like “sunrise,” “sunset,” and “high noon.”

As time went on, people began to make use of the fact that the sun follows a predictable path through the sky each day. This path was divided into imaginary parts (hours) of equal length from sunrise to sunset. Although different ancient societies experimented with different numbering systems, today’s analog clocks are based on a system where daylight was divided into twelve equal parts. The following definitions applied to the daytime hours:

  • Sunrise, by definition, occurred at the “sixth hour” in the morning.
  • Noon was the “twelfth hour.” To be “noon,” two conditions had to obtain: (1) the sun had to be due south; (2) the sun had to be at the highest elevation above the horizon that it would be all day.
  • The next hour after twelve was the “first hour.”
  • Sunset happened at the “sixth hour” after high noon.

Why wasn’t there a “zeroth hour” in this counting system? The Roman numeral system on which the modern clock dial is based did not have a “zero.” It started with “one.” Adding “zero” to the list of counting numbers was the development of another society; today, the corresponding set of number symbols are called Indo-Arabic numerals.

The definition of the 6th, 12th, and 6th hours applied whether the daytime hours were short (as in winter) or long (as in summer). If the sun was on the horizon, it was the 6th hour of the morning (or evening), exactly. Before the invention of clocks, people understood and accepted that hours would vary in length throughout the year, and even from day to night. Summer hours were long and nights hours were short. And it was just the opposite in the winter.

Further comments on the meaning of an hour

While an hour can be thought of as a length  of time, it should be noted that the sun’s hour-angles in the sky, themselves, are better understood as points  in space  as well as points in time. Professional astronomers still use “hours” … in a measure similar to longitude that is called “right ascension” … to identify a star’s location east or west of a point on the celestial equator (which looks like the earth’s equator, only much bigger and appearing to float above it … out among the stars).

The following sentences use “hour” two different ways: “The sun is at the 10th hour. In 15 minutes, it will be a quarter past 10.”

In the first usage, note how the hour is a point in time … “The sun is at the 10th hour.” In the second usage, see how an hour is used as a length of time … “In 15 minutes, it will be a quarter of an hour past the hour of 10.”

Now what’s this about local time vs. standard time?

In the old world of sun-in-the-sky time and, later, with the early usage of shadow poles as sundials, all time designations were what we moderns would call “local time.”

Local noon in Houston occurs when the sun appears due south of Houston (and, not coincidentally, at the highest point above the horizon that it will be all day). Similarly, local noon in San Antonio is when the sun appears due south of San Antonio. Likewise, local noon in El Paso is when the sun appears due south of El Paso.

In the old days, when there was no instant communications between cities, it didn’t matter that local noon just doesn’t happen at the same time for Houston, San Antonio and El Paso. These three cities are located in places that are east and west of one another; the rotation of the earth causes the sun to cross the southern compass point at different times for each city. For San Antonio, local noon comes about 12 minutes later than for Houston, and El Paso’s local noon is about 44 minutes later than Houston’s.

When people walked or rode a horse across the country, these differences were not important. But when America and Canada started laying tracks and building stations for the great intercontinental railway system, it became impossible to print a table of train arrivals/departures for scores of cities if each town’s local noon variations had to be accounted for.

So standard time was invented.

The history of standard time in the United States and Canada began November 18, 1883 when United States and Canadian railroads instituted standard time in time zones. Before then, time of day was a local matter, and most cities and towns used some form of local solar time.

With Standard Time replacing local time, and with accurate clocks counting hours that do not vary in length from day to night or from season to season, modern people have broken the connection between sun location and the time indicated on a time piece. Nowadays, you have to read the newspaper … for your own city … to tell today’s times for sunrise and sunset. It will be different for places that are east/west of you or north/south of you. But that’s another story from Astronomy 101.


watches - analog vs digital


TimeNavigator’s response to “Discard Digital Watches? Not So Fast!”  This was an earlier post about the Detroit School System’s going back to teaching with analog clocks.

When I was a young computer analyst, I was what some might call an “early adopter”  … you know, that guy that runs out and buys every new electronic gadget that comes out.  So when the first affordable digital watches came out, I knew I had to have one.

My first digital watch was a beauty. It had (I thought) a real coolness factor. Get this … it used red LEDs for the numbers! You had to press a button to get ’em to light up and shine through the watch’s dark crystal. And you could see what time it was in the movie theater without being irradiated by the radium dial on your wristwatch!

(Glow-in-the-dark wristwatches with radium dials … now that  was cool … Too bad someone had to figure out that they were not as safe for your health as first thought. Especially for the manufacturers.)

The first thing that struck me about my new watch was this. It told you the exact time, but it wasn’t so good at giving you’re a sense of where you were in your hour or day.

To know that, it took mental arithmetic and a mathematical interpretation of the result to sense whether a new hour was just starting, halfway through or almost over.

Now for a computer analyst, doing that calculation was trivial. But the fact remained that you had to be numerate (you know, the numeric equivalent to being literate) to use a digital watch to sense how far you had gone through an hour … or the day.

I still loved my cool digital watch. To this day, I drift back and forth between wearing digital and analog watches. Each format has its uses and pleasures.   — JLF

Digging Wells and Telling Time in Niger

learning, clocks, dials, historicalDigging Wells and Telling Time in Niger – By Joseph Finch

The following post relates to Time Navigator Web Pages that treat how pre-clock people told time by tracking the sun in the sky. Click here to read more.

Even today, in the 21st Century, there are people in the world that use sun-hours to tell time.

Around the globe, there are large groups of people living at technology levels that are equivalent to the 1700’s (if not before) in the Western World. Not having access to clocks and watches, many of these still use hand signals to talk about daily points in time.

Here’s a back story that leads to a modern example of this old time-telling practice.

A friend of mine is working with Baptist Missions to train villagers in Niger to install and maintain pumps to bring water to their villages.

These villages are not on any roads. They have no electricity or running water … anywhere. Most homes have dirt floors, and the walls and roofs are made of mud and thatch. Cooking is done outdoors. The daily routine for the women in the village is generally like this:

(1)    Make breakfast.

(2)    Gather pots and jars to carry to a distant water source (hand-dug wells, streams, rivers) to bring water back to the village.

(3)    Prepare the evening meal.

Going for water and walking it back to the village may consume half (or more) of the productive labor of the village’s women each day. Besides any issues of lost woman-hours, the quality of the water brought back is very poor. It is mostly surface water that is heavily polluted by livestock, wildlife and general sanitation issues. Yet less than 200 feet straight down, is an ample supply of clean water … despite the fact that this people is living in a very arid region.

To boot-strap the quality of life for the vast numbers of people living in the area, two Baptist organizations (the Global Mission Partnership Network and the International Missions Board) have covenanted to train the villagers to drill, install and maintain their own wells. The Mission Boards understand that water facilities have to be a home-grown effort. By doing their own work, the villagers can install a well for as little as $200. To use a contractor to do this would cost as much as $5,000. For these people, this is the difference between “can” and “can’t.” Moreover, when the village men “own” the pump, they are in a better position to decide when/how to fix it if it breaks, and they are in a better position to decide when it’s time to install more wells in the village.

Besides providing a better water supply and allowing the village’s female labor force to be better used, the installation of water pumps raises the possibility of crop irrigation.

The region’s rainfall ranges between 5-10 inches per year (that’s in the wetter south-western portion of the country, if there’s not a drought going on). The staple crop of the village’s larder is millet. This is a fast growing, short season crop that is well suited to Niger’s hot, dry climatology. With a good millet crop once a year, the villagers can have something like two meals a day for about six months after the harvest. After that, supplies run low, and the village diet can drop to one meal a day. With irrigation, the millet crop could be supplemented with other crops, and the agricultural season could be lengthened. This would improve the villagers’ lives by expanding their larder to have more food (and more kinds of food) for a longer period of time during the year.

Drilling a water well … and telling time … in Niger

In John 21:17, the Lord commissioned Peter to lead His church, saying (among much more), “Feed My sheep.”

Sometimes this can be accomplished by showing the Lord’s people how they can prosper their own lives.

This was the mission that Dan Friend of the GMPN, Chris Riggs of the IMB, and others responded to as they joined a program to train African locals how to drill their own wells.  An important feature of this project was that the wells had to be drilled using only man-power, simple tools, and low-cost materials that are readily available on the local economy. Dan, Chris and the others were trained stateside on the designs and methods to be recommended for the Africans’ use. Then the team traveled to Niger to see if the theory would actually work in practice. It did.

As an old TimeNavigator, my ears perked up when Dan was telling me how the mission team came together with the locals to dig a practice well. On the first day of work, there were a couple-dozen men (locals and Team) getting their hands dirty in the project. When the sun went down, work stopped. (I wonder if the locals considered that to be at 6pm, exactly … customs vary, you know)

Supper was to come next, but while there was a crowd, Dan asked the Village Chief through an interpreter when the men were to come back to work the next day. The Chief considered this and then raised his hand to show where the sun was to be, above the horizon, to start the day. The locals understood this, and the moderns (on reflection) decided that he meant 9:30am. And it all worked out.

Even in modern times, we can run across the primitive roots of time telling. For eons, smart people have done what it takes to keep their societies organized. When there are no resources available but pointing at the sun to track the time, then that becomes a good thing to do.

– -Joe- –

Aug 23, 2013

Discard Analog Clocks? Not so fast.

Discard Analog Clocks? Not So Fast.
Blog by Deborah Williams:
Based on Detroit News article by Maureen Feighan

Do you think analog clocks/watches are on their way out? Here’s why they may not be.

Sometimes, the latest is not the greatest. Educators in Detroit have learned that very lesson and have chosen to teach their young ones to tell time the old-fashioned way—with analog clocks rather than digital ones.

Writer for The Detroit News, Maureen Feighan, recently penned an article, “Metro Detroit Educators Teach Telling Time Old Fashion Way,” in which she outlines the reasons that educators in Detroit have decided that students do not learn a real sense of time with digital clocks … Several schools are installing analog clocks “to help students not just learn to tell time but understand the concept of it.”

Some of these schools have only analog clocks, and some have both digital and analog clocks.

They have good reason for this change:  These educators acknowledge that children are able to read the time on a digital clock, but that “doesn’t mean they understand the concept of time or the increments of time — hours, half-hours, minutes and seconds,” explains Jim Burt, principal of Detroit’s Workman Elementary.

Not only that, the educators note that analog clocks help with skip counting by 5s, ideas like clockwise and counter-clockwise, and with fractions when the clock face is used to demonstrate half- and quarter-hours.

Furthermore, these educators are encouraging parents to have analog clocks at home and to reinforce these important concepts in the following ways:

Keep an analog clock at home.

Practice counting forward and backward between 1 and 12 and counting by 5s.  Being comfortable with numbers connects to all other skills in elementary math.

Talk about the language and vocabulary of telling time — half past, quarter past, etc.

For smaller children, count down to coming events, such as going to the park or Grandma’s house; gradually move on to longer time frames.

Use a paper plate to make a permanent display of an analog clock. Mark family times that are significant, such as meals or bedtime.




Welcome to Time Navigators!

Welcome to Time Navigators, your on-line resource for adventures in time, space and math.

clocks, calendars, learning, math, time

[Click pic to jump to TimeNavigators Home Page]


    The TimeNavigators website is dedicated to the development and promotion of resources leading young minds to have a fascination with and an understanding of the means of tracking and marking time.
   The navigation of time begins with an understanding of some of the key elements of astronomy and math. The sciences of time measurement (horology) and the stars (astronomy) grew up together like twins. The development of mathematics provided the underpinnings needed for an increasingly accurate tracking of time.
    In addition to clocks and calendars, this website talks about games designed to help young Time Navigators master the arts of addition, counting and multiplication.
    Though the reading of clock dials by pre-schoolers can be taught mostly as a matter vocabulary (learning the names of the parts of a clock dial … like “one,” “two,” “three”), such learning is a gateway to mastering counting and the higher arts of addition and then multiplication.
    To date (July 2013), TimeNavigators’ has been the effort of a single author (Joseph Finch) to develop resources to support pre-school and elementary students’ needs in understanding time, math and some “gateway” aspects of astronomy.
    The hopes of this site are that it will …
  • Provide constructive feedback from/to a community of resource developers on what works and doesn’t work with new educational resources and to offer  suggestions for carrying those ideas further.
  • Offer a platform for dissemination of educational resources to the world at large for those who have ideas that are slated to enter the Public Domain.
  • Build a network of interested inventors, parents and teachers to help them support one another in their endeavors.

The calendar wheel artwork in the figure above is Copyright Joseph Finch, 2013. Please see “Handling of Copyright Material” elsewhere in this blog for permissions and restrictions on the use of this copyrighted material.