A Brief History of Time Counting

From a one-time sundial to today's cesium clock or optical clock, the measurement of time has gradually become more and more subtle. Since when is it necessary to measure this time? Why or why not? Why is it necessary to make that measure more subtle? How did so many different places come under the same system? Professor Shubhdeep Dey, who himself is currently researching the most modern instrument of measurement, is giving a surprising answer to these questions.

Many of us are familiar with the name "A Brief History of Time" due to the book written by Stephen Hawking. In the first part of this article, I will give a brief discussion about the history of "time calculation", which is different from the history of "absolute time". Time is something that is beyond the reach of human beings. Absolute time can never be measured but time calculation is a completely mechanical matter. The instrument can measure the time difference between two events. The practice of counting time dates back to the beginning of modern science. But the beginning of time itself is from the birth of our world, that is, from the Big Bang. So in that sense, the history of time counting can be called a newborn baby.

Why was it necessary to calculate the time

Horology is the process of measuring time and making the necessary mechanical instruments for it. Measuring time is basically an event that reliably repeats itself. Approximately thirty thousand years ago, humans found such an event in different phases of the moon (29.5 days of a full orbit around the earth, the same phase of the moon is repeated). The idea that lunar time can be measured by looking at different phases of the moon, however, did not occur to humans in the beginning. That came much later when the time needed to be calculated. Since ancient times, the need to calculate time from the finest to the finest has been felt, as well as the technology of time calculation. Where once the sundial was used to measure time, now atoms are brought to absolute zero temperature by the use of lasers to measure time. Today's state-of-the-art atomic clock is one of the finest man-made instruments. The finesse of measuring time has reached an unprecedented level.

The first question that comes to mind when discussing the different methods of calculating time and their sources is: Why do people need to calculate the time at all? I have read many reasons for this. The reason for my personal preference was that a time calculator was needed to ring the prayer bell at certain times of the day, depending on the position of the sun and moon in different places of worship. This, of course, is one of the many possibilities, although many sources have suggested it. However, the main point is that measuring how far the day went in relation to sunrise or sunset was the first urgent measure. Gradually people also realized that the seasons can be determined by measuring time because the length of the day varies according to the seasons (of course it is also possible to determine the seasons through various observations of astronomy). If you can determine the season, there is a lot of profit in farming.

In ancient Egypt, sundials were used to measure time during the day. The use of sundials has also been seen in other civilizations such as Persians, Greeks, and Romans. Over the course of several thousand years, at the very beginning of the nineteenth century, measuring the time of the sundial has become more accurate.

History of time counting in India

One of the traces of a sundial still found in India is a thirteenth-century sundial at the Sun Temple in Konark. Then there is the Jantar Mantra of Jaipur, made by Raja Joy Singh in the eighteenth century. Yantar-Mantar's sundial was the largest sundial in the world at that time. Later King Joy Singh made similar sundials in Delhi, Benares, Mathura, and Ujjain. In addition to the sundial, these instruments contain many other modern instruments for the practice of astronomy. (In this connection, it should be noted that the practice of astronomy in our country is older than many developed countries and even today I am ahead of my developed countries in various fields of astronomical research.) Time calculations were needed to ensure this change of position. Therefore, the need to calculate the time has come from astronomy.

There are more modern and more accurate sundials than these older sundials at IIT Roorkee and at the IUCAA in Pune where I work (Inter-University Center for Astronomy and Astrophysics). Pictures of all these sundials are shown in Figure 1. Apart from these, there are probably many more sundials in India beyond my knowledge.

If you look at it that way, the use of sundial was common in our country till a few decades ago. I remember in the late eighties my grandmother could tell the time by looking at the shade of a toggle tree in our home garden in Burdwan. This is also a kind of sundial book! It is customary to tell the time by looking at the length of the shadow based on the position of the sun, but not long ago.
 

Some problems with the sundial

To measure the exact time at different times of the year with a sundial, you have to work a little harder. As the latitude of the earth is tilted by 23.5 degrees, the length of day and night increases and decreases throughout the year. The seasons also change for the same reason. So the shadow that is seen in summer can be said to be a time, that shadow is seen earlier in winter. Moreover, sundials have to be made latitude-dependent because as the latitude of the earth increases, so does the altitude of the sun.

Even if these issues are caught, some problems remain. For example, the Earth's rotation axis itself completes a circle every 26,000 years, or it may change slightly due to natural causes such as volcanic eruptions. So it is not possible to make a perfect sundial despite hundreds of attempts for various reasons. As time goes on, the error in the measurement of that clock will also increase.

Light clock, water clock, hourglass

In addition to sundials, the Chinese used an oil-lamp-dependent watch. In this watch, time was calculated based on how much oil was left in the container. Perhaps their main use was in religious ceremonies so that the ceremonies could be completed within a certain time. But later the common people also started using it. A refined version of the oil-lamp clock is the candle clock, which has some marks on the candle and the time can be measured with the help of those marks as they burn.

But it should not be expected that such a watch will give the right time and each lamp will give the same time. How fast a lamp burn depends on what the lamp is made of, what kind of environment it is lit in, how many mistakes are made in staining, all of this.

The Egyptians again invented a kind of water clock. There is an empty pitcher with a mark on it and a small hole in the center. The kalsita is then placed in a container filled with water. The water slowly enters the jug and until the jug is filled, an estimate of the time is obtained from the stains. This type of water clock was used in the ancient Indus Valley Civilization of India. In Dravidian, it was called "ghatika yantra" ("clock" in white). This type of watch has also been shown in the Bollywood movie 'Mohenjo-Daro'.

Hourglass became very popular in the early thirteenth century, especially among sailors at sea. Particles like liquid or fine sand were used in such clocks. The Middle Ages saw the emergence of more precise timekeeping clocks, such as the clocca ("clocca", Latin clock). I have heard that such a clock is still hanging on the wall of a church in Italy.