The Story of Time (Nita Berry)

A CBT PUBLICATION TOhfe TSitmoery Nita Berry



By Nita Berry- Illustrated by B.G. Varma Children's Book Trust, New Delhi

The Story of Time won the Shankar's Award and First Prize in the category Non-fiction/Information in the Competition for Writers of Children's Books organized by Children's Book Trust. Apart from stories, the other works by the author, published by CBT, are The Story of Writing, The Wonder of Water, Rajendra Prasad and Vinayak Damodar Savarkar in 'Remembering Our Leaders' series. EDITED BY GEETA MENON AND SUDHA SANJEEV Text typeset in 13/17 pt. Palatino © by CBT 2001 Reprinted 2002, 2003, 2004 (twice). ISBN 81-7011-891-3 Published by Children's Book Trust, Nehru House, 4 Bahadur Shah Zafar Marg, New Delhi-110002 and printed at its Indraprastha Press. Ph: 23316970-74 Fax: 23721090 e-mail: [email protected] Website: www.childrensbooktrust.com

The Riddle Of Time Just suppose you could clamber aboard a Time Machine and press the 'Forward' button. Z...a...ap... Would you hurtle forward through a blinding flash of days and nights, months and years—even long centuries— perhaps, to land into an alien world of the future...? A world that will be a marvel of technology. And then suppose you pushed the 'Reverse' button and took a trip in the opposite direction— g journeying into the dim recesses of the past. You might just land right into your favourite period of history... Imagine a scene, set in ancient Macedonia. A gleaming, black steed is resisting all efforts to tame it. It rears wildly and throws every rider to the ground—until a handsome, curly- haired youth, who has been watching intently, approaches it. He murmurs gently into its ears, and turns the quivering creature to face 3

the sun, away from its moving shadow. This has been disturbing the horse all along... If you could re-enter the past, what a thrill it would be to watch young Alexander tame the splendid Bucephalus who would later lead him to victory in all his battles! Or to see for yourself the lavish Mughal court with its 'nine gems'. You might even travel further back into the primitive world and wander through dinosaur country, with a friendly brachiosaurus, perhaps, for company! Can man indeed travel through time? So far, it is only in the pages of science fiction that he has travelled at will into the past and the future. Or, of course, in his dreams which can take him into any period every night! However, he has always dreamt of conquering time which, more than ever before, rules our lives with a firm hand, without ever seeming to slow down. Could you think of a world without time? Imagine what it would be like not to have to tumble out of bed to the shrill buzz of the morning alarm and to hurry to catch the school bus! To be able to play on endlessly without being told that it was time to go home... or to watch a late night, horror film without it ever being bedtime! It all sounds too good to be true, or even practical for that matter, does it not? For a world without time would probably be a totally chaotic place to live in, where 4

everything happened all at once—a kind of topsy-turvy land! Without time you would be late for school or forget to go to bed at night. You would either reach the cinema too early or after the show is over. And how embarrassing to arrive at your best friend's birthday party after all the guests have left! Without the steady ticking of our clocks, nothing indeed would run smoothly anywhere. Factory machines would work in absolute disorder; and buses and trains would run at all hours, instead of to a schedule. On the other hand, life without time could perhaps be a kind of timeless existence, where nothing moved forward and existed in a static state. It is difficult to imagine either state, actually. No doubt, you do know what time means to you, because it is so very important. You probably look at your watch or clock at least a dozen times in a day. Yet, if you were asked to explain 'time', you would most likely be too perplexed to answer. Time is a funny thing. It can mean different things to different people. It is rather like the story of the six blind men who felt the elephant. Remember how each one gave his own description of the animal! Similarly, if you asked for a definition of time, you would probably get a lot of varied answers. For a physicist, time along with space makes up the two basic building blocks of the



universe. A science fiction enthusiast probably Napoleon Bonaparte views time as the fourth dimension. A (1769-1821) biologist, on the other hand, will see time as the internal rhythm of our bodies that keeps us in harmony with nature. For the watch manufacturer, time ticks away as accurately as his timepieces. Time means money to the busy businessman. As for the student taking an examination, time is always running short! What about when you are bored? Time just does not seem to move on, then! However, for some people time has no meaning at all! The great French General, Napoleon Bonaparte was a strict disciplin- arian. He was a stickler, too, for time. Once he invited some important generals over to dinner. When the guests failed to arrive on time, he sat down to eat a solitary meal. He then asked his servants to clear the table and put away the rest of the food. When the generals arrived, they were surprised to find no dinner. Napoleon calmly announced that dinner time was over and it was now time to leave. It was a bitter lesson on the value of time! \"So, what then is time?\" You might well ask, just as St. Augustine did as far back as the fifth century A.D. He had gone on to comment, \"If no one asks me, I know what it is. If I wish to explain it to him who asks me, I do not know.\" This most familiar of concepts used in organizing everyday thought and action is also the most elusive! 7

It cannot be given any simple definition. \"We physicists work with time every day/' the late Nobel laureate Richard Feynman remarked once. \"But do not ask me what it is. It is just too difficult to think about!\" Modern physicists, mathematicians and philosophers are determined not to let time slip through their fingers, eager to probe its many mysteries. They have been thinking hard—what really is time? How did it begin? Can it be reversed or even slowed down? After all, who has not wished to turn back the clock or calendar at some time—to redo a test perhaps, or erase a mistake? Again, they have wondered, could time be accelerated to move 'Fast Forward', rather like a video cassette? When did the universe come into existence? Will it expand forever and the galaxies fade and disperse into an ultimate 'heat death'? Or will it recollapse into nothing, so that our descendants are doomed to share the fate of an astronaut who falls into a 'black hole'? And then, will time end? The questions are as endless as they are puzzling. Early man too probably realized that time was passing, when he saw he lived in a world of constant changes that time was passing. Seasons came and went. Rocks crumbled into dust. He watched buds bloom into beautiful flowers and wither away. Little babies grew into young men and women, before time made them old and grey. He saw that nothing or nobody 8

lasted forever. Since those early days, man has Albert Einstein tried to measure the flow of time. In fact, (1879-1955) devising more and more accurate clocks and calendars became one of his most prolonged, intellectual pursuits. It was as if he could understand time better by measuring it. \"We have given more attention to measuring time than to anything in nature,\" remarked Gemot Winkler, Director of Time Services at the U.S. Naval Observatory, Washington D.C. \"But time remains an abstraction, a riddle...\" Despite our mastery of clocks and calendars, the nature of time itself is still a mystery. Time, as we see it, moves forward, somewhat like the flow of a river. To us, it therefore implies change in the physical sense. After all, development, growth and ageing do take place with time. Scientists who agree with this idea of time are called 'relationists'. However, some scientists feel that time exists, independent of the physical universe. They explain, it is rather like a container in which the universe exists and change takes place. It would have, therefore, existed even if the universe had not. Albert Einstein was one such scientist who believed in this 'absolutist' theory of time. Time began to be seen as a dimension like height and width. To make matters even more confusing, other thinkers argue that time depends on the existence of conscious beings, in the mind

alone. Without consciousness, there is no time! So far, these differing lines of thought have not come to a common conclusion on the nature of time itself. Yet, whatever their differences, the vast distances of space and time have held all men spellbound. Since the dawn of history, man has looked up at the mighty universe and gasped in awe. On a clear, starry night he must have been fascinated by the millions of twinkling stars, some bright even fiery, others a faint pinpoint. What great secrets do they hold, you may well wonder. Many of these pinpoints of light are thousand times larger than our earth. They are giant suns, blazing balls of molten metal and rocks, billions and trillions of miles from the earth. It is their enormous distances from the earth that make them appear tiny. Small distances, such as the length and breadth of this book, are measured in centimetres or inches. Bigger distances are measured in metres or feet, while still bigger distances are measured in kilometres or miles. However, sizes and distances in the universe are too vast to be measured in terms of any of these units. The stars of our galaxy whirl together in space in a gigantic spiral, so vast that ordinary words for describing hugeness just cannot describe this. Even millions or billions of miles would not be enough to express these immense distances. We need an 10

altogether different unit for measuring them. Scientists describe the size of the universe by using a measurement known as a light year. This means a distance so great that it would take a beam of light a whole year to travel from one point to another. To have an idea of the immensity of this distance we must first measure the speed of light. Light travels at an enormous speed, faster than anything else we know. It covers 1,86,000 miles per second. This means you would zoom more than seven times around the world in one second! It has a speed more than 5,00,000 times faster than the Concorde. Now calculate how far light will travel in a year. The distance will be about 58,80,000,000,000 miles. This distance is called a light year. Time thus becomes an essential unit for measuring the great distances of space. Scientists have calculated that the star farthest from the earth, visible to the naked eye, is more than eight million light years away. And if we use powerful telescopes, we can see stars even 1,000 times more distant than this! Light from them takes over 8,000 million years to reach us. This means that when you look at them, you are seeing them as they were 8,000 million years ago! Some of the stars you can see in the sky have, probably, ceased to exist long, long ago. Calculations show that our galaxy of stars is 2,00,000 light years across. In other words, 11

it would take a beam of light 2,00,000 years to travel right across the galaxy. It is easier to think of it this way than to try and remember the actual distance, which would be written out as 1,200,000,000,000,000,000 miles! You would lose count of the zeros! Thus it is simpler to use the light year as a unit when dealing with distances beyond our understanding. How old is the universe? When we start thinking about its origin and age, we run into real trouble with time. Some scientists believe that the universe came into existence at one particular moment. They call this the 'Big Bang', which happened a long, long time ago. Others think that the universe had always existed and will exist forever, that is, there is no beginning and no end to time! It is difficult Solar System

to grasp such an idea, either. However, recently it has been broadly accepted that time cannot be treated in isolation from space. The union of space and time is now being seen as a key to understanding the universe. Man's recent experiments in space have been successful in sending planetary probes to some of our 'nearby' and more distant neighbours in the solar system—remember, when we say 'nearby' it is in space terms, and is actually millions of miles away. At the same time, physicists and mathematicians are working hard to push the boundaries of our understanding of the universe, and to solve the riddle of time. Looking ahead into time, therefore, becomes an enthralling challenge.

Time In Our Lives 75...74..T3...72 hours... The time bomb ticked away inexorably, strapped tightly to Dr. Cabaleiro's chest. It was timed to explode in just 72 hours if a ransom of 10 million pesetas (Rs. 12 lakhs) was not delivered by 4 p.m. the next day, at a lonely spot outside Orense, Spain. Dr. Cabaleiro had become the victim of a new type of kidnapping in Spain, where a person is released to collect his own ransom after a live bomb has been attached to his body. Dr. Cabaleiro was on the edge of panic. After all, he was a walking time bomb! Wild thoughts raced through his head. Perhaps he should get away from people. 'I should head for the mountains and just wait for this to explode... No, that is madness. The kidnapper was confident there would be no accidents... 14

and, anyway, this bomb could be a fake...' Only his family and two close friends knew of his agony. The wily kidnappers had threatened serious consequences to his family, if the police were informed. Now, in less than 20 hours he would be blown to bits if he did not find the money... Fifteen hours to go! The hours seemed to be slipping away as Dr. Cabaleiro's friends urgently tried to make contact with eminent Orense citizens to raise the ransom money from different banks early the next morning. It was a race against time! It was now already noon with only four hours to go for the deadline. At last, with a 15 kg brown suitcase of thousand-peseta notes in his hand, the time bomb ticking loudly

against his chest, Dr. Cabaleiro drove 77 km out of Orense, following directions. He stumbled and panted 3 km through rocky terrain, his heart beating painfully against the bomb casing. The kidnappers had promised to leave instructions on defusing the bomb after receiving the ransom money. Dr. Cabaleiro just could not locate the place described on their hastily scrawled directions. Frustrated, he returned home. Three hours later, the kidnappers telephoned, with a more accessible spot. By the wee hours of the morning he had finally found the place, and deposited the money in a bag left there by the kidnappers. It was 12 hours past the deadline! He looked around helplessly. There were no instructions left anywhere on how to defuse the bomb. It was all a terrible trick! In desperation Dr. Cabaleiro contacted his family. They had already informed the police. He was to drive straight to Orense Police Headquarters where a special bomb squad had been flown in. It took three hours for the bomb disposal unit of the national police to detonate the explosive. Seven kilos lighter, Dr. Cabaleiro was in a state of shock as he stepped out of the explosive ring of death, barely in the nick of time. Later that day, the deadly bomb was detonated by experts in an empty field, by remote control. Fragments were blasted four storeys high and 25 metres from the site. 16

Time can thus become a crucial factor in a life-death situation like this one, where it almost ran out! Every minute becomes precious. Our newspapers sometimes carry stories of extraordinary, real life dramas where danger is measured in minutes and even split seconds. You may have read about the last minute rescue of somebody who has fallen on a railway track, before a speeding train whizzes past, or from a blazing inferno, before everything is engulfed in flames. Those crucial seconds often mean all the difference between life and death. However, exciting dramas in actual life do not occur all the time. Nonetheless, in our own lives we are deeply aware of time constantly, and indeed measure our existence by it. Our entire lives pass by to the steady ticking of clocks. Time plays a vital role even for the most ordinary purposes. We are rushing for buses and trains and connecting flights, and time is often fixed for appointments with the dentist or school principal. So the measurement of time becomes most important for us. We wear wristwatches that tell us the time even if there is no clock around. Every home has at least one clock. Take a look at your own day. You are probably awakened in the morning when your alarm clock says, \"Get up.\" In very little time you have brushed your teeth and are ready for school. It is important to be on time, or you 17

will be punished for coming late. In school, lessons are held according to the class time- table, and the buzz of the bell tells you when a certain period is over. If you have a test or classwork, you look at your watch even more than usual to make sure that you finish in time. Back home, life follows a pattern according to time, and before you know, it is bedtime! The days run into weeks, and weeks into months and suddenly you are a whole year older! It certainly is time to celebrate. The calendar that hangs in your room helps to plan things over the year. It would be difficult indeed to live without clocks and calendars. They help us save time as well as measure it. There is a saying, 'A penny saved is a penny earned.' One might just as well say, 'A minute saved is a minute earned.' If you work wholeheartedly, you could easily save a minute here and a minute there to finish a job faster. By the end of the day, you could save an hour from all these little minutes. In a year's time these hours would add up to precious week's, even months! Imagine what they would amount to over five years! So, if you do not dawdle over things but do them on time, you do well both at work and at play. Take care of the minutes and the hours will take care of themselves. And never do tomorrow what you can do today! Ever remember, a stitch in time saves nine! Many old proverbs like these tell us to make the 18

most of our time. After all, time and tide wait for no man! See if you can think of any more of these time tested sayings! Even as you look at a clock and watch a second tick away, it is gone. For us, a second as a basic unit of time seems adequate. Actually our clocks and watches do not need to be accurate to more than half a minute or so in our daily routine. Certainly, they should not run much slower or faster. If your school bus arrives at the bus stop at 7 o'clock every morning, it is not much point going there at five minutes past seven, is there? Sometimes, however, we do need more accurate timing. Track events and swimming meets are timed in fractions of seconds. It can make all the difference between being a winner or a loser. Our technological world needs even more precise time. An astronomer makes his calculations based on fractions of a second. A navigator at sea or in an aircraft, plotting location by satellite, relies on a time signal which is accurate to within a single millionth of a second (microsecond). You will be astounded to know that scientific technology has split the microsecond even further. Spacecrafts like the Voyager II are guided by radio signals timed to the nanosecond (0.000000001 of a second). Physicists tracking motion inside an atom reckon in picoseconds (thousandths of a 19

Babylonian shadow stick nanosecond) or even femtoseconds (thousandths of a picosecond). Such minute splitting of seconds is mind-boggling, to say the least. If you find it difficult to grasp, look at it this way. There are more femtoseconds in a second than there were seconds in the past 31 million years! During the last few years, clocks have been perfected so well that even if they were not altered for a thousand years, they would still give you the time, correct to within a second. Time touches us all, young and old, city and village dweller alike. We live our lives according to pattern, based on the clock or calendar. Though village life follows a more leisurely pace than life in the city, the farmer must follow seasonal patterns, to sow and to reap his harvest at proper times. You may have heard your grandparents or older people talk of the 'good old days' when the relentless ticking of clocks did not rule their lives. Communication was slow. People often embarked on journeys by foot or bullock cart which took months altogether! Today, as man progresses in all spheres of activity, it has become vital to make the most of time. Modern telex fax machines, electronic mail or e-mail have made communication practically instantaneous. Time is really what you make of it! 20

Nature's Time Divisions Do you have a baby brother or sister at home who wails when you are fast asleep, or is hungry long after everybody has eaten? If you do, you may be sure he is, in some ways, quite like our early ancestors. For they too had little sense of time! They seemed to live in a 'timeless present' when they hunted or ate or rested, with little or no sense of either the past or the future. Yet, even in the beginning, when man was little better than a savage, he would watch that great, golden ball, the sun, arcing across the sky everyday. He saw the wonder of the sunrise as the sun spread its red rays to bring daylight into a dark and sleepy world. As the sun moved high overhead, man knew it was time to hunt and fish. And later, when the buds closed and the birds flew home to their nests,; 21



he saw darkness setting in on earth with the setting sun. It was time to go back to the safety of his cave to rest. He did not quite understand where the sun came from, or where it went every night, but he certainly did feel day and night occurred. And he realized that it had something to do with the regular coming and going of the sun. Many thousands of years hence, man was a much cleverer being, for he now knew many more things. He was still fascinated by the vast sky above, and studied the movements of the sun and the heavenly bodies. It would be a long time yet before he had any proper clocks, but he could guess the time of the day just by looking at the position of the sun in the sky. It was his first clock. The sun seemed to move slowly but surely, in a wide curve from east to west. It was easy to recognize sunrise and sunset, but more difficult to tell when it was mid-day. That was when the sun is highest above the horizon and right overhead. Man came to recognize that half the daylight hours were spent when the sun lay between the two positions that marked sunrise and sunset. He knew then that it was mid-day or noon. At night, the movement of the stars in the sky served the same purpose. Man noticed that as the night passed, different groups of stars became visible. They seemed to form pictures in the sky in the shapes of men and animals. 23

Waxing and waning of the moon He learned to tell the time at night by looking at these star pictures as well. The sky was indeed a kind of gigantic clock that man was learning to read quite well and to tell the right time of the day. Indeed, even in those far-off days, it was important for him to know when he was supposed to be somewhere. For was not there a certain time for the temple, a time for meeting friends, a time for work and for play...? The idea of the month probably came with the observation of the changing shapes of the moon. Man noticed a strange thing in the sky. The moon seemed to grow bigger and become round in 15 days till it became a full moon. After that, over the next 15 days, it appeared to become smaller before finally disappearing from the sky altogether. This was a regular cycle, he noticed which spread over 30 days, before it started all over again. It is likely that the change in seasons gave birth to the idea of the year. The cold, windy winter when man huddled before a fire to keep himself warm was followed by spring. Then the earth turned green and joyful, the birds sang and flowers bloomed. And then came the blazing, hot summer when the earth became parched and dry, and everything dried up. The monsoons provided some solace from the heat. And leaves fell off the trees in autumn before winter came once again. This cycle of seasons covered about 365 days or a whole year. 24

It was, therefore, quite early in history that Early telescope man started counting time by days, months, seasons and years. These were really the first beginnings of the calendar. In ancient times, man had a very simple picture of the universe. He believed that the sun, moon, stars, and planets were small objects that moved round the earth. The universe was taken to be a great dome over- head having glittering lights. Below, in the centre of all creation, lay the vast, flat, immovable earth around which everything else moved. It was only in the sixth century B.C. that the idea of the earth being a sphere was first suggested. Ten centuries later, the sun was suggested as the centre of the universe. Then came the invention of the wonderful telescope that actually saw much more than what the human eye could see or even imagine. Man had a better way of looking at the vast expanse of space around him. As more and more facts were gathered and knowledge grew, our modern idea of the universe gradually developed. Scientists tell us that our earth is a planet, a globe nearly 8,000 miles in diameter, which moves round the sun. The sun itself is a star. Actually, it is much smaller and less bright than many of the stars in the sky. Only it seems so big and hot to us because it is much closer to us than any other star. The distance of the sun from the earth is about 93 million miles, 25

The earth spins on its axis which does seem a huge distance. If you journeyed to the sun in an aircraft at a steady speed of 1,000 miles per hour, you would not arrive for ten years! However, considering the vastness of distances in space, this figure is not really very much. Just as it appeared to our ancestors, the sun seems to us too to rise in the east and journey across the vast archway of the sky before setting in the west. At night it disappears altogether from our sight. This movement does not actually happen, but appears to do so. The sun at night is in exactly the same place as it was during the day. It is we who have moved! We know now that the earth is like a ball that spins on its axis. If you were to stick a knitting needle through the ball of wool, it will be very easy to understand what this means. The ball represents the earth, and the knitting needle is the axis of rotation. Day and night occur because the earth makes one turn on its axis every twentyfour hours. When one side of the earth faces the sun, we have daylight. When the same side of the earth turns away from the sun, we have night. While we are fast asleep in the night, someone on the other side of the earth is waking up to start a new day, because his part of the earth is turning towards the sun. We could understand better the occurrence of day and night by actually experimenting 26

with our ball of wool and a torch in a darkened room. Place the lit torch on a fable, and shine it directly on the ball of wool. The torch is the sun and the ball, naturally, is the earth. What do you see? The 'torch-sun' lights up one side of the ball, while the other side, which is not facing the 'torch-sun', is in total darkness. Now rotate the ball slowly on the knitting needle 'axis'. Each part of the ball gets illuminated in turn. Parts which were dark or had 'night' are now lit up to have 'day', while the lighted parts move into the dark side. Day thus turns into night. This is exactly what happens to the rotating earth.

Rotation of the earth The sun appears to us to move because of the earth's rotation. The period taken for the earth to make a complete turn from west to east, a 'day', was our first unit of time measurement. Man later divided this into 24 shorter periods called hours. Some of these hours occur at night and others in the daytime. Remember that the 'day' of 24 hours is not all daylight. It consists of both daylight and night. We, however, call it a day in science, which does seem to be rather muddling at first. Did you ever realize that you are living on a great, big spaceship? Every day and every night! If you have travelled at 66 miles per hour in a car, you know how fast trees, houses and people seem to whizz past. Imagine what it would be like if you were to move 1,000 times faster! That is the speed at which the earth travels round the sun—66,000 miles an hour! Even the world's fastest jetliner, the supersonic Concorde, moves about 1,450 miles an hour. That is why living on the planet earth is just like riding a great spaceship. It is faster than anything we can imagine. You should remember that the earth moves in two distinct ways at the same time. We just saw how it rotates, spinning like a top on its own axis, causing day and night to happen. The second kind of movement is its revolution round the sun. It moves at an amazing speed in a great circle round the sun, 28

covering every day 15,84,000 miles. The earth's full journey of about 5,84,000,000 miles round the sun takes nearly 365 days and six hours to cover. Like all the ancients, people in the great civilizations of Babylon and Egypt were drawn to the movement of the heavens and the changing seasons. It was probably their regular occurrence that gave birth to the idea of the year. Thus the Babylonians developed a 'year' of 360 days, which was about the time the earth took to make its long journey around the sun. The practical Egyptians extended this year by five days which they set aside for feasting during the annual flooding of the river Nile. So the 365-day solar 'year' came into use. After the 'day', the year was the next unit of time measurement to be drawn up. However, although a round figure of 365 days seemed accurate enough to use in everyday life, it was not really very exact, and created many problems in the early calendars, as we shall see soon. Clever improvements by the Romans and by Pope Gregory XIII Revolution of the earth round the sun

in 1582 gave us today's Gregorian calendar, which is accurate to a day in every 3,323 years. With man's progress in science, he has accurately calculated that it takes the earth 365 days and five hours, 48 minutes, 45.5 seconds (and another 1/100th of a second) to make a complete circle round the sun. As you can see right away, it is quite impossible to divide our calendar to include those extra hours and seconds. So, we just say that a year has 365 days. We do not throw away the extra hours but save them up very carefully. Every fourth year is called a leap year, when we add a whole extra day to the year to make it 366 days long. So we manage to stay even again with time. If we did not do this, think of* the total mess our calendars would be in! They would just keep falling further and further behind. In a matter of a few hundred years we would have February where January ought to have been! If you are good at maths, you can figure out yourself when leap years are coming. Every year that is exactly divisible by four is a leap year. Remember, there should be no remainders. However, there is one exception. If you are looking at the years at the turn of the century, like 1900 or 2000, they must be divisible by both four and 400 to be leap years. Now calculate—yes, 2000 A.D. was a leap year but 1900 A.D. was not. Nature's third time division was drawn up 30

by a thorough study of the movements of the moon, that shiny, white disc in the sky that does not stick to one shape. It takes on different shapes on different days. The ancients were enthusiastic moon-gazers! They observed that the interval between one fully round moon and the next is always about 30 days (29.5 days to be more precise). This lunar 'month' became their third unit of time measurement. Science tells us that this is the time taken by the moon to complete one revolution round the earth. The moon is actually a natural satellite of the earth. It travels round the earth, just as the earth travels round the sun. The moon is much closer to the earth than anything else in the sky. It is about 2,34,000 miles away. That is why it looks so large! If you were to travel ten times round the earth's equator, you would cover a greater distance than that between the earth and the moon. Down the ages there were lots and lots of stories about the The moon goes round the earth thirteen times in one turn round the sun, or one year.

moon, that it was made of silver or cheese— or even had a man who was supposed to be watching you! It was popularly believed that the moon was the land of the dead, where everything went after life. Dark areas on its surface were given fanciful names like 'Sea of Showers' and 'Sea of Nectar'. Scientists have now found that the moon is a dead world. It has no air, water or life of its own. Even its bright light is not its own. Then, how do we see it shine at night? The moon reflects the light sent to it by the sun. The sun lights up one side of the moon at one time. So the moon appears to change its shape at different times of the month and we see different 'phases' of the moon. When the moon is between us and the sun, we face its dark side. We cannot see it at all.

We call this 'no moon' the 'new moon'. Phases of the moon However, when the earth is between the sun and the moon, the lit side of the moon faces us and we see the 'full moon', big moon as a crescent, a 'half-moon' and a three quarter disc. The old sky watchers observed that twelve lunar months covered a complete cycle of four seasons, or one year. So they divided the year into twelve parts of 30 days each—the twelve months. However, once again, as with the year, there were difficulties with the early calendars. So months were lengthened or shortened, even though they were originally linked with the phases of the moon. We find today, not all the months are of the same length. January has 31 days while February has only 28 or 29. It is not difficult to see how these three earliest time units are nature's own time divisions. The day depends on the earth's rotation on its axis, the year upon its journey round the sun, and the month upon the moon's journey round the earth. The earth is a faithful timekeeper. Never has the day, month or year fallen back in time, although today's astronomers say it is losing a fraction of a second per century! Once man realized how well earth keeps track of time, he sought to measure it himself with a variety of the strangest devices. These were our very first man-made clocks. 33

Telling Time By Shadows It was a blazing, hot morning. The sun beat down bright and strong, making all living creatures scurry for the shade. Early man sat in the cool shadow of a leafy tree. He was armed with big hunting sticks and spears, but it was too hot to look for a meal that morning. He was content to lie there, chewing juicy bits of fruit. In a while, he was fast asleep. When he awoke, the sun was right overhead. He blinked hard. It seemed hotter than ever, for the shade had almost disappeared. Indeed, the shadow of the tree had shortened to a mere stump. Moreover, it had moved away from him. Early man grunted irritably and moved into the little, dark patch. There was not another tree for miles around. There were some big boulders, but their shadows too had virtually disappeared. 34

Soon the sun began to go down. The .tree's shadow lengthened once again, although it had moved around in a kind of semi-circle. Early man found that he had to keep moving every now and then to stay within the shade. Why could he not sleep in peace at one spot? He grumbled to himself. He found he had moved half a circle round the tree following its shadow. He did not know why the shadow kept moving. Maybe it was some kind of dark creature...he really did not know! All he knew was that it was good for a cool nap. Much, much later, man observed that whenever something came in the way of light, a shadow was formed. No, the shadow was not a creature at all! Rocks, trees, even hills, all had shadows in their own shapes. He saw that when he walked in the sun, he too made a shadow on the ground. It walked when he walked, and it stayed still when he was still. He realized that his shadow was formed because he stood in the path of sunlight. He looked at the shadow with interest at different times of the day. It was strange that it never remained the same size for long! In the morning, when the sun was low in the sky, how long his shadow was! It became shorter and shorter as the mid-day sun rose overhead. In the evening, it grew long once again as the sun dipped towards the horizon. The direction of shadows changed too, as the direction of the sun changed. We know 35



now that shadows form in the direction opposite to the source of light. Also that the length of the shadow depends on the angle at which the sunlight hits the object. Since the sun changes its position in the sky all the time, the direction as well as the length of shadows keep changing. Man did not know all this at that time, but he was trying to understand things as well as he could. He thought hard, and even began to experiment. When he stuck a twig into the ground, he found that its shadow, too, grew or shrank in the course of the day. It also moved round the twig in a kind of half-circle as the sun moved in the sky. The size of the shadow began to give him an idea of the general time of the day. A clever thought struck him. He firmly stuck an upright pole into the ground, out in the open. Like everything else he saw, its shadow too moved with the position of the sun. He marked the progress of the shadow cast by the pole with some stones which he placed around the pole. He looked at his stone markings the next day and the next. He saw that every day, at different times, the pole's shadow fell on the same markings. * With practice, man became cleverer still. He could judge the position of the sun simply by noting the position of the pole's shadow! Earlier, he had begun to recognize sunrise and sunset, and even mid-day, by looking directly at the position of the sun in the sky. 37

However, in between these times, it was difficult to tell the time by the sun's position. Man found that he could measure the passing of time more accurately by watching shadows, than by looking at the sun and trying to guess the time of day. Man had actually made the first crude clock! Of course, it was nothing like the clocks we have today, which have an hour and a minute hand moving round a dial. But it was the simplest way to measure time. Shadow sticks helped people tell the time long before proper clocks were invented. It is believed that the Babylonians first used these early clocks as long ago as 5,000 years. Naturally, these peculiar clocks worked only when the sun was shining, and could not be used at night, when there were no shadows! 38

This simple shadow and pole arrangement The shadow clock was the basis of the various shadow clocks which were used by the ancient Egyptians between 800 and 1,000 years B.C. The shadow clock was a clever invention, although not a very accurate timekeeper. It was a fairly simple device, consisting of a straight base placed in an east to west direction, on which stood a crosspiece. This crosspiece was placed at the east end of the base in the morning, and shifted to the west end in the afternoon. As the sun's rays fell on the crosspiece, it cast its shadow on the base. This was marked by a scale of six time divisions, so intervals of time could be measured. We know that daytime is never of the same length over the year. Summer days are much longer than days in winter, when the sun rises late and retires earlier to bed as well, just like some of you do! In north India, for instance, you must have seen how summer days stretch to over 14 hours, while the winter days are barely 10 hours long, and your play-time is shortened. This variation in daytime increases as one travels further north. Clearly, these changing lengths of daytime would create many problems while using shadow clocks. For the 'temporary' hours, as their time divisions were called, would vary over the year in length. An early Egyptian schoolboy would find, to his greatest dismay, 39

Egyptian shadow clock that a class in the summer months would really stretch longer than it did in the winter! He must have fidgeted restlessly during those hot hours, and probably earned a caning from his irate teacher! However, the Egyptians have not completely discarded clocks of this kind, for they are still in use in primitive parts. From the shadow clock, it was an easy step to inventing the sundial which is, in reality, a shadow clock, for it too depends on shadows cast by the sun to tell the time. It is said that the people of ancient Egypt and Mesopotamia developed the first sundials. In fact, the earliest known sundial still preserved is an Egyptian shadow clock about 3,000 years old. It consists of a stick raised above the ground, and a circular dial with markings for hours around it. As the sun changed its position in the sky, the length and position of the stick's shadow falling on the dial would change as well. The Egyptians divided the day between sunrise and sunset into twelve periods of time, which were marked on their sundials. They divided the night too into twelve time periods, corresponding to the rising of twelve stars. Why did they have twelve divisions and not eight or ten? We do not know for sure, but the twelve-hour time division may have been taken from the numbering system of Mesopotamia, or from star patterns they saw in the sky. 40

Our 24-hour day is, in fact, Cleopatra's needle based on this ancient Egyptian division of day and night. Actually, there is nothing occurring in nature or in the world that has anything to do with having 24 time divisions in the day. They were made by man for his own convenience. In those days sundials were made of blocks of wood with pointers. Later still, huge stone columns were used. By carefully working out the markings on the dial and the tilt of the pointer or arm, it became possible to make a good sundial. This could measure ordinary hours of uniform length, instead of the old 'temporary' ones that kept changing with the seasons. The Greeks and Romans took the idea of the sundial from the Egyptians. It was probably better than any other time- measuring instrument they knew. From them it spread to Britain and other parts of Europe. Cleopatra's needle, at present, on the Thames embankment in London, was once part of a sundial. Smaller sundials were 41

A sundial used too. One small Egyptian sundial, about 3,500 years old, is shaped like an 'L'. It lies flat on its longer leg, on which marks show six periods of time. The shadow cast by the shorter arm would fall on the divisions to indicate the hour. About 300 B.C. a Chaldean astronomer invented a new kind of sundial, shaped like a bowl. The shadow of its pointer moved along and marked 12 hours of the day. This kind of sundial proved very accurate and was used for many centuries. In fact, sundials of all shapes and sizes came into popular use. Some were crude structures, others amazingly accurate. The glass on an unusual sixteenth century sundial focused the rays of the noon sun onto some gun-powder in a cannon. A regular explosion at 12 noon was its effective time signal! Pocket-sized sundials were most popular in the eighteenth century. On the other hand, the enormous eighteenth century sundial at Jaipur has a triangular gnomon or stick 44 m high. Its huge shadow falls on a curved dial which measures 30 m across. This is the world's biggest sundial. The sundial was perfected over the centuries to tell the time accurately. In a good sundial, the pointer directly faces the north or south Pole Star. It slants at an angle equal to the latitude of the place it is in. A vertical pointer will show the right time only at one latitude 42

and in one season. Hour marks A sundial are spaced unequally on a flat dial. However, sundials today are built in gardens more as decorative pieces than for their usefulness. It is easy enough to make your own sundial, and to see for yourself how our ancestors measured time. Set up a 'shadow stick' in the open. Carefully mark its shadow at different hours of the day on the dial. Note the time above each shadow. Your 'clock' is now ready! You can read these markings to tell the time correctly enough if you cannot find your watch. Remember to keep this sundial fixed firmly in the same place. However, once the sun goes down, or it begins to rain, you will have to look at your watch again to know the time! 43

Water-clock—water turns the Man Keeps Track Of Time drum which winds the hands. People used sundials for at least a thousand years to keep track of the hours. Yet, they found that they needed to know the time more accurately, and often when it was raining or cloudy. Like us, they sometimes wanted to know the time at night too. What could they do then? After all, shadow clocks were quite useless when there was no sunshine. Necessity is the mother of invention. Not surprisingly, people devised other means to measure time. Many of these seem most strange, and even amusing to us in the peculiar ways that they worked. They did not resemble our familiar clocks in the least. However, they were popular timekeepers of long ago, both during the daytime and the night. The inventive Egyptians again put their imagination to work, to develop the water- clock or 'clepsydra'. This device measured 44

time by the gradual flow of water. If you were Water-clocks to look at it, you would laugh, for this 'clock' merely looked like a big bathtub full of water! The water-clock was actually a basin- shaped, stone vessel with a small hole at the bottom. Its inner walls were marked with divisions to show the hours, so the 'clock' was easy to read. To start the clock, the vessel was filled to the brim with water. As the water ran out through the hole in the bottom, the level of water in the vessel kept falling. When the water level dropped to the first mark on the walls, it indicated that the clock had been running for one hour. If the water level fell to the next mark, it showed that the clock had run for two hours. In this way, as marks were exposed, the time could be read. The clepsydra was a simple clock, but rather cumbersome. It certainly could not be carried around to tell the hours! Archaeologists have discovered water-clocks, some over 3,000 years old, in Egypt. In the oldest water-clocks, it is interesting that the wall markings do not allow for the fact that as water drained out, pressure was reduced and its flow slowed down. So the time these early water-clocks indicated could not have been too accurate. In India and China, water-clocks of another form were used. An empty, brass pot with a small hole in its bottom was set afloat in a big vessel of water. The brass vessel slowly filled with water, and within a set time sank to the 45

Plato bottom of the big vessel. Watchkeepers of the (427? 347 B.C.) hour would sound a loud gong before fishing out the bowl and setting it afloat again for the next time interval. Even the primitive Indians of North America and some African tribes used a similar kind of water-clock. This consisted of a small boat which was filled with water through a hole till it sank in the pond or stream it was floated in. Imagine the tribesmen diving into the water at the oddest of hours to retrieve their 'clock'! Later, the Greeks and Romans made water- clocks that were more complicated devices, although they worked on the same principle. The Roman water-clock consisted of a cylinder into which water dripped from a reservoir. This caused a float to rise and gave readings against a scale on the cylinder. However, these water-clocks were not reliable methods of telling time, and had to be checked frequently against a sundial. Do you have an alarm clock that rings loud enough to wake you up early for school? School students seem to have been traditionally startled out of their sleep down the ages! Even 2,400 years ago, drowsy Greek students jumped out of bed to the shrill whistle of their alarm clock. And this was probably loud enough to make them jump out of their skins as well! The ancient Greek philosopher Plato 46

invented an ingenious alarm clock by fitting a A water-clock siphon (a bent tube used to transfer liquids from one vessel to another) to water-clock. As soon as the water was level with the top of the siphon, it ran down a tube into a vessel below so quickly that the air in it was compressed, and escaped through a pipe with a piercing whistle. Plato effectively used this device to summon his pupils for classes at the unearthly hour of 4 a.m. It is not likely that they could have continued to sleep once their alarm clock went off! Since this had to be set six hours beforehand, Plato probably did not get much sleep himself as he set about adjusting it! Water-clocks were used for a variety of purposes. Orators's speeches were timed by them, so one knew when to tell them to stop! They later became the first clocks with movable parts. About 140 B.C., the Greeks and the Romans used the toothed wheel to improve the water- clock. Water dripped into a cylinder and made a floating piston rise as it trickled in. This piston was connected to a toothed wheel. The wheel moved a pointer which served as the single hand, the hour hand, of a clock. It gradually turned from one hour mark to another, on a dial. The Chinese civilization flourished in the Orient, with the development of many remarkable inventions, independent of the rest of the world. In the eleventh century A.D. 47

A sandglass a Chinese scholar, Su Song, constructed an enormous clock that was among the first mechanical water-clocks. It had a 12-metre high tower and was worked by a 20-tonne bronze waterwheel complete with shafts and levers, for 1.5 tonnes of water! Su Song's clock signalled the quarter hours with gongs, bells and even a musical instrument. So people living around just could not say that they did not know the time! As late as the sixteenth century, the famous scientist Galileo used a mercury water-clock to time his experiment on falling bodies. The principle of the water-clock, where the reservoir emptied in a set time, was also the principle of the sand-glass, invented much later. Only, fine sand was used instead of water. Initially, this 'clock' looked rather like a flower pot with a hole at the bottom. The pot was filled with sand which dropped through the hole into another pot below. The lower pot would fill up in a certain time, and so give indications of time. Although these clocks were smaller than water-clocks, they were rather messy and did not become very popular. About 2,000 years ago, people developed still another kind of sandglass. You may have seen this rather delicate looking instrument in some kitchens for the egg-timers we use today are a type of sandglass. It consisted of two hollow glass vessels, 48