Four Historical Dials

131004-03 4-dials thread (1)

FOUR DIALS: A Brief History of Clock Design:
Before sundials and clocks, hours were positions of the sun in the sky.
Shadow poles were the earliest community time devices.
The first mechanical clocks had only one hand … the hour hand.
The minute hand was added when clocks became accurate enough to justify the addition.
(Text above is from public domain sources. Google is the source of the images.)


131004-03 4-dials thread (4)

These four dials follow a historical sequence that shows how the telling of time grew … (1) From watching the sun in the sky … (2) To watching its shadow on the ground … (3) To a one-handed, mechanical simulation of the sun’s shadow on the ground … (4) To the addition of a minutes hand when clocks became accurate enough to make that worth while.

Together, these four dials provide the foundation of an introductory study of time for our young TimeNavigators. These four dials could be used in a classroom, for homeschooling, or just as a neat, scientific-looking decoration in your kid’s bedroom.

Possibly, the best way to introduce these dials to young TimeNavigators would be one-at-a-time. Hang the Sun-Sky Dial on the wall, by itself, for a period of days or even weeks. During that time, mentor/tutor the young TN to understand what the dial means and how early people used sun position to tell time. The Sun-Sky Dial uses a 24-hour movement to simulate the sun’s movement throughout the day.

Next, the Shadow-Pole Dial is hung besides the Sun-Sky Dial for another period of time. The process of mentoring and tutoring is repeated to help the TN understand how the shadow on the ground marked the sun’s position in the sky.

The third step is to mount a third dial besides the other two, a dial with only one hand. It is a generalized replica of the earliest western clocks that also had only one hand … the hour hand.

Finally, the fourth dial, the one with only a minute hand, is mounted besides the others. The addition of this dial mimics the historical step of adding a minute hand when the accuracy of new clock mechanisms made this addition worthwhile.


The First Dial

131004-03 4-dials thread (2)The TN web site has a good blog post for putting this dial into a modern context. Please see  “Digging Wells and telling time in Niger” for a story of how reading sun-hours in the sky is still being done in modern times.

(Text above is from public domain sources. Google is source of image.)

131004-03 4-dials thread (3)

This dial uses a 24-hour movement to simulate the passage of the sun through the heavens above and beneath the earth below through the 24-hour cycle of a day.

The Sun-Hours Dial is designed to introduce young TimeNavigators to the way people once used to tell time. With this dial, our kids can begin to learn the names of the hours and learn how the vocabulary of sun-hours relates to times of day. People often talk about what happened yesterday or what needs to happen tomorrow. To tell yesterday’s story or describe tomorrow’s plan, you’ll have to talk about when things happen.

  • Before sundials and clocks came along, one way to reference time was to talk about where the sun is, was or will be in the sky. Examples of this are:
    •We left right after sunrise.
    •It’s high noon now. Let’s start the feast.
    •We stopped 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 people were involved in agriculture, which of course, 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) in the sky. Just as you can look at your watch today to see if it’s really getting late, they could watch the sun 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. 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 “when the sun is high.”

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 parts (hours) of equal length. 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” … the Roman list of counting numbers 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 the winter) or long (as in the 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 the lengths of hours would vary throughout the year.

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 sometimes better understood as points  in space  as well as points in time. Professional astronomers still use “hours” 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 [of an hour] past the hour.”

  •  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 a length of time … “In 15 minutes, it will be a quarter [of an hour] past the hour of 10.”


What Time Is It? How do we put the words together to call out time?

Suppose the sun lies between the positions of 10 and 11 in the sky and you are asked what time it is.

A simple answer could go like this: If the sun is halfway between the two points, you can say, “It is half past ten.” The words used to call out this time consists of  (1) first stating the name of the most recent hour, the tenth, which is a point in time, (2) and then giving an indication of how much time, if any, has passed since that hour arrived.

We can also reference forward to the next hour. Suppose that the sun is three quarters past 10. Instead of saying “It’s three-quarters past ten,” you could say “It’s a quarter to eleven.” To make this statement, you have still referenced a point in time, the 11th hour, and indicated a length of time that separates you from that point in time.

Please see “Handling of Copyright Material”


The Second Dial

131004-03 4-dials thread (5)

SHADOW POLES were the earliest community time devices 

The earliest time measurement devices were sundials, hourglasses, marked candles and water clocks.

Shadow poles … the simplest sundials … could be used as time keepers for a whole community. And shadow poles in different fields spread across town were always perfectly synchronized.

By definition, they accurately showed where the sun was in the sky by marking where the tip of the pole’s shadow was on the ground.

When two people looked at the tip of the pole’s shadow on the ground, they could easily agree on the time indicated.

If local time is defined by where the sun is in the sky, and the difference between short winter daytime hours and long summer daytime hours doesn’t matter, then shadow poles are perfect.

(Text above is from public domain sources. Google is source of image.)

131004-03 4-dials thread (6)

The Shadow Pole Dial

The Shadow Pole Dial is designed to introduce young TimeNavigators to the second historical stage in methods of tracking time.

Shadow poles were the earliest community-wide time tracking devices. They were simple to erect. All that was needed was an open field and a vertical post of any convenient size. Because of the sun’s great distance, the sun’s shadows across the entire local area are perfectly parallel and synchronized … to the accuracies that anyone could measure at the time. This means that all the shadow poles across a region could easily be set up to tell the same time. Moreover, reading time against marks on the ground overcame some of the problems associated with the error-prone process of looking up at the sky and trying to estimate sun angles against an empty sky.

As noted in the introduction to the Sun-Hour Dial, reading a sun-hour in the sky was an eyeball estimate. It was hard to do accurately, and different people were likely to guess different sun angles and times. On the other hand, the ground around a shadow pole could be marked (with stones, etc.) to provide a concrete reference for people to use in measuring shadow angles. A shadow pole on the Commons became a place to meet and to see and be seen. Though simple in concept, the village shadow pole (and the grounds around it) often became very elaborate and were sometimes treated as works of art.

The Shadow Pole Dial design uses a modern 24-hour clock movement to simulate the movement of the sun’s shadow around the base of a pole. The “stator” is a fixed graphic element attached to the inside of the dial cover … between the observer and the rotating part (rotor) of the dial. The white areas shown in the illustration are cutouts that allow parts of the rotor moving beneath the stator to be seen. The “rotor” is a flat plate attached to the hour hand of the 24-hour movement. During the 6am to 6pm daytime interval, the rotor shows the sun moving through the sky and its shadow on the ground moving in response. During the dial’s 6pm to 6am “nighttime  ,” the rotor shows an imaginary star and its imaginary white “shadow” moving a half-day out of phase with the sun and its shadow. (An imaginary star and its shadow are a little funky, but we felt the nighttime display needed something. Watching nothing go by on a simulated sundial at night would be relatively boring, at least to most people.)

 Local sun-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, time designations were all what we moderns today call “local time.”

Local noon in Houston occurs when the sun seems to be 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 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 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 watches and clocks  becoming common,

This dial’s movement rotates at a constant rate to give a rough approximation of what’s happening outside your window as the sun climbs across the sky. It is designed to teach the idea of the sun moving through the sky and its shadow moving around the shadow pole. If you happen to live at the eastern edge of your time zone and it happens to be the first day of spring or fall (or if you live on the equator), the movements of the sun and its shadow are reasonable representations of what’s happening outside.

Please see “Handling of Copyright Material”


The Third Dial

First clocks - one handed


The first mechanical clocks had only one hand … The HOUR HAND

The earliest clocks were made to simulate the motion of a shadow pole’s shadow on the ground.

If you live above the 23rd latitude, the pole’s shadow on the ground always moves in the direction that is now called “clockwise.” If the common clock had been invented below the equator, where the pole’s shadow moves in the opposite direction, then “clockwise” might have been defined differently.

One-handed clocks are easier for kids to “get into.” The clockwise motion of the hand becomes basic. Where the hour starts is clear. And the concepts of quarter-past, half-past and quarter-till are right there on the dial to see.

Once these features are understood, the student is ready for the minute hand.

(Text above is from public domain sources. Google is source of image.)


One-handed dial is easier to use 72CR

A Brief History of Dials

Clocks existed before clock faces. The first mechanical clocks, built in 13th century Europe, were mechanical devices that struck a bell to announce the hour, calling the public to prayer . (The German word for Bell is Glocke.) To ensure that the bells were audible, these were erected as tower clocks in public places. It was not until these mechanical clocks were widely used that their creators realized that their wheels could be used to drive an indicator on a dial on the outside of the tower, where it could be widely seen.

The Hour Hand

Before the late 14th century, a fixed hand (often a carving shaped like a hand) indicated the hour by pointing to numbers on a rotating dial. After this time, the current convention of a rotating hand on a fixed dial was adopted.

The Minute Hand

Minute hands (so named because they indicated the small or minute divisions of the hour) only came into regular use around 1690, after the invention of the pendulum and anchor escapement increased the precision of time-telling enough to justify it. St John the Evangelist, at Groombridge, Kent, has a fine example of a clock with only an hour hand.

The Second Hand

In some precision clocks a third hand, which rotated once a minute, was added in a separate sub-dial. This was called the ‘second-minute’ hand (because it measured the secondary minute divisions of the hour), which was shortened to ‘second’ hand.


The convention of the hands moving clockwise evolved in imitation of the sundial. In the Northern hemisphere, where the clock face originated, the shadow of the gnomon on a horizontal sundial (like a shadow pole) moves clockwise during the day. This was also why noon or 12 o’clock was conventionally located at the top of the dial.

About the One-Handed Dial

This dial allows kids to start reading clock dials quickly and easily. If your child is not up on his/her numbers beyond counting to twelve, this will not be much of an issue. The early learning achieved by kids using this dial is more a question of vocabulary … “naming the animals” … than arithmetic.

The one-handed dial reflects the design of some of the earliest mechanical clocks used in the Western World. Those early clocks used only one hand. With that one hand, they could show when each hour had arrived and indicate how much time had passed since the start of that hour.

When a child learns to read a standard clock, the process is complicated by the fact that the clock has two hands. The learner has to identify with two clock parts that move differently, have different functions and mean different things. Even smart kids in 2nd and 3rd grade can have problems sorting this out when it’s all presented together.

By eliminating one hand, this dial breaks clock reading down into easier tasks that can be mastered even by pre-schoolers. With the minute hand gone, the learner can focus on what the hour hand indicates and how fast it moves.

Learning Objectives


  • Learn the names of the hours
  • Learn that an hour can be a POINT in time (like “it’s ten-o’clock)
    or it can be a DURATION of time (like “we are in the 10th hour”)
  • Learn the names of the quarter hours
  • Learn what clockwise means
  • Extra credit: Learn that football, basketball and dollars have “quarters.” Here, the word “quarter” can be treated as vocabulary – it means one of four parts. The teaching of math/fractions need not be a learning objective for the young learners … but later, this can become a gateway concept for certain learning.


Minute Hand added when clocks more accurae

THE MINUTE HAND was added when clocks became more accurate

In 1577, Jost Burgi invented the minute hand while building an improved clock for the famous Danish astronomer, Tycho Brahe.

Tycho made the most accurate body of measurements of star and planet positions of anyone before the invention of the telescope.

Tycho’s student, Johannes Kepler, used Tycho’s data to prove that Mar’s orbit was not a circle but an ellipse and that the sun was at a focus of that ellipse.

These and other observations revolutionized astronomy by confirming that the sun, not the earth, was at the center of the Solar System.

(Text above is from public domain sources. Google is source of image.)

Minutes-dial adds new function 72CR

About the Minute-Hand Dial

This dial adds the idea that an hour can be measured in more detail with a new hand that moves faster and turns a full circle in only an hour, instead of half a day.

By keeping the Hours and Minutes Dials separate for one more step in learning, the young TimeNavigators can stay focused on learning the difference in the ways that the two hands work.


When a child learns to read a standard clock, the process is complicated by the fact that the clock has two hands. The learner has to identify with two clock parts that move differently, have different functions and mean different things. Even smart kids in 2nd and 3rd grade can have problems sorting this out when it’s all presented together.

By eliminating a hand, the two Hours and Minutes Dials break the reading of time down into easier tasks that can be mastered even by pre-schoolers. A one-handed dial helps the learner to focus on how fast each hand moves and how to read the time it indicates.

Learning Objectives


  • Learn the names of the minutes
  • Learn to count to 60 by 1’s and 5’s
  • Learn to relate “15”with quarter-past
  • Learn to relate “30”with half-past
  • Learn to relate “45”with quarter-til
    (does anyone ever say three-quarters-past?)
  • Learn that clockwise is still clockwise



The Final, Combined Dial

Combined Hours-Minutes Dial 72CR

This Final Dial Combines the “Look” of the Hours and Minutes Dials to Emphasize How a Standard Clock Is Simply the Combination of These Two Functions

This last dial intentionally repeats the graphics and formats of the individual Hours and Minutes Dials. This “look” is used to reinforce the learning that went into understanding how to read the Hours and Minutes Dials.




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