Early Ways of Telling Time
One of the oldest and simplest ways of telling time is by looking at the position of the sun. Over time, early people realized that when the sun appeared, the light part of the day started, and when the sun disappeared, the dark part started When the sun is low on the eastern horizon, people know that the time of day is sunrise, when daylight is just beginning. When the sun is low on the western horizon, people know that the time of day is sunset, when daylight is just ending. When the sun is at its highest point in the sky, people know that the time of day is noon, or midday, when daylight is about half over.
Since early times, humans have wanted more detailed information about the passage of time than sunrise, midway, and sunset provide. Much of the information early humans wanted about time involved meeting common needs, such as when was a good time to go hunting.
About 3000 BCE, early Egyptians told time by the shadow cast by the sun on an unmoving object. They used an obelisk, a vertical structure with four sides, as a shadow clock, placing it in the sun so that it could cast a shadow. The shadow showed the position of the sun throughout the day. By 300 BCE, people in Babylonia had started using a sundial, a flat circle on which a 12-hour clock face, or dal, had been written. Adapting methods used by the early Egyptians, Babylonians attached a gnomon, a vertical marker to the middle of the dial. The gnomon cast shadow on the dial as the sun’s position changed throughout the daylight hours. Where the shadow fell on the dial showed the time of day.
In addition to using the position of the sun to tel time, people used to learn the position of the moon, plants, and stars. However, on overcast days and nights, people found it difficult or impossible to tell time and began to invent tools for tracking time. The early Greeks and Egyptians designed a water clock (also called a clepsydra) that used the flow of water t measure time. In a very early version, water flowed through a small opening in one container onto another bowl-shaped container below it. Both containers were usually made of stone or heavy pottery. Horizontal lines were drawn on the bowl-shaped container. The water reaching each line showed that a certain amount of time had passed.
Another method of telling time at night was used by ancient China and involved tying knots at regular intervals on thick rope, then burning the rope. People could tell how much time ad passed by looking at how many knots had been burned. Once candles has been invited, people used them not only to provide light, but also to tell time at night. First, thick candles were burned t see how long they would last. Then, notches were made in candles of similar thickness were, each notch representing a period of time. A person could tel how much time had passed by looking at how many notches has been burned since a notched candle was lit.
An economic activities became more complex, people began to think of ways of telling time that are more accurate, lasted longer, were more easily carried than sundials, sand timers, and water clocks, and could be used at any time of the day or night. The hourglass was in use in Europe by the 11th century, could be used at any time and was one of the first timekeepers (also called timepieces), tools designed to tell time that we not dependent on the sun. The hourglass consisted of two upright containers joined with a narrow opening. The first containers were probably made of pottery, and the later oneself glass. One container contained sand or some other material, such as water, that shifted easily. To start the process, the hourglass was turned upside down so that the sand orator poured into the bottom container.
The units of time measured varied by how large the hourglass was, the size of the opening for the sand to run through and how long it tooth sand to fill the bottom hourglass. A small hourglass Ould be used for measuring minutes, or large one for measuring an hour or more. The larger the hourglass, the heavier it became and the more difficult was to make it measure time accurately. However, by the 11th and 12th centuries, hourglasses were one of the most portable and accurate ways of telling time. For those reasons, hourglasses wee often used as timekeepers on ships, which needed accurate measurements of time to determine longitude, imaginary lines or meridians that run from the North Pole to the South Pole on the Earth’s surface.
Did you know?
In the 14th century, hourglasses, also called sand timers, were used in law courts to let people know when the yard to stop talking.
Time was important on ships because sailors were required to take turns keeping watch for things such as storms, rocks, icebergs, land, and other ships. Captains might ring a bell once every half hour during certain watches. For this kind of short timing, 30-minute timers were used.
Activity 1:Making a Sundial to Tell Time Using Sunlight
Purpose: To investigate an early way go telling time by using sunlight.
- Round piece of cardboard about 6 inches (15.25 cm) in diameter, one for each student.
- Sheet of Bristol board or heavy craft paper
- Sunny day
- World History Journals and pencils
Most Montessori teachers present this concept in Year 4.
Announce that the students will have the opportunity to investigate one way early people tracked time during daylight.
Discuss ways people could tell time during daylight without referring to clocks and watches. Talk about situations where it might be useful to know how to tell time without using clocks or watches.
Explore with students what they know about shadows when they stand out in the sun at a particular time of the day. For example, their shadows lengthen or shorten with the rotation of the Earth around the sun.
Ask the students to imagine standing in the same place for 12 hours of daylight and watching their shadows moving around them, making out the hours.
Say that instead of standing in the same place for 24 hours, the students will make sundials that do the same job, then check the accuracy of the sundials with the clock.
DEMONSTRATING A SUNDIAL
Demonstrate the materials for making a sundial.
Use a ruler to place a dot in the center of the cardboard circle.
Cut a piece of craft paper intern isosceles triangle with the two equal sides at least 2 inches (5 cm) long.
Make a 1-inch (2.5 cm) fold along one of the sides of the triangle. This flap will be used to glue the triangle to the cardboard circle to form the gnomon.
With the point of the triangle on the center of the circle and the other end of the triangle facing the outside of the circle, glue the triangle to the circe to make a sundial.
With the students, take the sundial outside and place it in the sun. Use a pencil to mark the time from the classroom clock where the shadow of the gnomon falls on the base. Tell the students that if they had started a sunrise and come out regularly during the day to make where the gnomon’s shadow fell, they would see that the shadow from the gnomon moved completely around the base from sunrise to sunset and that they could make a 12-hour clock face on the bae.
Invite the students to make their own sundials and lace them outside for a small exercise. The students will use the classroom clocks to mark the fist time, then return to the sundial at least four times over the day to mark the sun’s shadow and compare it to the time on the classroom clock.
Ask the students to use their journals to record the results of the exercise.
Working in pairs, choose a place outside and mark it with chalk. One student stands in that place once an hour over the day, and the other student measures the shadow cast. Then together make a chart of how the standing students shadow shortens and lengthens through the day,
Research another early way of telling time by using sunlight (e.g., obelisk), write a short description, and draw a picture of it.
Activity 2: Making a Water Clock to Tell Time Without Sunlight
Purpose: To investigate an early way of telling time in the dark (I.e., without sunlight or a watch).
- Glass jar
- Paper cup that fits about halfway into each jar
- Straight pin
- Strip of paper marked with five horizontal lines 1 inch (2.5 cm) apart.
- Transparent tape
- Pitcher of water
- World History journals and pencils
Most Montessori teachers present this concept in Year 4.
Announce that the students will have an opportunity to investigate one way early people told time without using sunlight.
Discuss the challenges early people might have telling time without sunlight.
Define and discus water clocks and hourglasses as examples of how early people could tell time without sunlight, also as ways people could measure short periods of time.
DEMONSTRATING A WATER CLOCK
Demonstrate the materials doe making a water clock.
Tape a strip of paper vertically to the side of the jar, making sur that the bottom of the strip is at the bottom of the jar.
Use the pin to make a hole in the center of the cup.
Place the paper cup so that it fits about halfway in the top of the jar.
Record the time on the classroom clock, then use the pitcher to fill the cup with water.
When the water reaches the first horizontal line on the strip of paper, record the time on the classroom clock. Repeat as the water rises and reaches the remaining lines on the paper strip. Point out that the time it takes the water to reach the top line is the longest time the students can measure with the water clock. In a similar fashion, an egg timer measures time for just tow minutes.
MAKING WATER CLOCKS
Ask the students to make their own water clocks and use them to time three different tasks or events (e.g.,billing an egg, eating lunch, walking around the school once).
Ask the students to use their journals to write about the usefulness and accuracy of their water clocks in timing the three tasks or events.
* Make anther kind of clock. Nail two boards into an L-shape. Take six paper cups and use a pin to place a hole in the bottom of the center of five of the cups. Using tacks, attach cups in a vertical row on the upright board, placing the cup without the hole at the bottom. Fill the top cup with water. To see how much time the water clock can measure, record on clock how long it takes the water to move from the top cup tot he bottom. Finish by writing a short report about how this water clock could be used.
* Find two examples of water clocks used in early history. Provide a brief description and an illustration (drawing or photograph).
* Find example of an hourglass timer that is in use today. Write a report explaining how the timer works and ways it can be used (egg timer, timer for board games).
* Make sand timer that measures an exact length of time, such as 10 minutes or 30 minutes. Report on the challenges involved in making a timer that can measure exact lengths of time.
* Research early clocks that used motion to measure time (e.g., perpetual motion clocks, rolling ball clocks). Describe two examples and explain why they are not practical for everyday use.