The Story of Time

A CBT PUBLICATION

The Story Of Time Nita Berry

By Nita BerryIllustrated 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, curlyhaired 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 views time as the fourth dimension. A 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 disciplinarian. 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

Napoleon Bonaparte (1769-1821)

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 tried to measure the flow of time. In fact, 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

Albert Einstein (1879-1955)

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

jS?.

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 timetable, 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

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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

g

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!

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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 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 overhead 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

Early telescope

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'. 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.

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Phases of the moon

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 shadow lei had movec Early man i every now, Why could He grumbl moved half its shadow, keptmovin creature...h< was that it ^ Much, n whenever s< a shadow w not a creatu all had shad that when h a shadow o: walked, anc He realizec because he: looked at th( times of the remained t morning, wh long his sha shorter as th the evening, dipped towc The direct the directior

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 s opposite to length of th< which the s sun changes the directioi keep chang that time, t things as w< He thou experiment ground, he 1 shrank in tin round the t sun moved began to gh of the day. firmly stud out in the o its shadow \ sun. He ma cast by the placed arou markings tl that every < shadow fell ' Withprac could judge noting the Earlier, he and sunset directly at t

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 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

The shadow clock

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, 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 timemeasuring 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

Cleopatra's needle

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.

A 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

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and in one season. Hour marks 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

A sundial

Man Keeps Track Of Time

Water-clock—water turns the 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 waterclock or 'clepsydra'. This device measured 44

*

•

>

time by the gradual flow of water. If you were 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 basinshaped, 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

Water-clocks

Plato (427? 347 B.C.)

bottom of the big vessel. Watchkeepers of the 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 waterclocks 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

m

invented an ingenious alarm clock by fitting a 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 waterclock. 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 water-clock

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

connected by a narrow 'neck'. The upper vessel was filled with fine sand, which trickled slowly into the lower vessel through the neck. It emptied the upper vessel in a precise measured period of time. Time intervals could also be measured by checking the amount of sand that had trickled through. The sandglass was inverted to restart its time measurement. No doubt, the measurement of time depended on the size of the glass vessels, the amount of sand and the narrowness of the neck. The top vessel could be filled with enough sand to flow through the neck for one hour. That is why the sandglass came to be called the 'hourglass'. On the pulpits, preachers often placed an hourglass which ran for a whole hour. Everybody could see how much longer sermons would last, and not surprisingly, many made use of this time to snatch forty winks on a Sunday morning in church! On ships, hourglass was invaluable in measuring time and even speed during voyages. Ships kept four hourglasses which timed the length of one watch, that is, a period during which part of a ship's crew are on duty. The hourglass was turned over at the end of each four-hourly watch. Another sandglass on board lasted only 28 seconds. It was used to time a length of line thrown overboard with a log at its end. The ship's speed could be calculated by counting 49

Sandglass/hourglass

Christopher Columbus (1451-1506)

the knots on the rope that ran out during these 28 seconds. The knots were tied at intervals of about 47 feet. Even today, sailors measure the speed of their ships in knots or nautical miles per hour. A land mile, as you know, measures 5,280 feet, but a nautical mile is longer, measuring 6,080 feet. The term 'knot' probably came from the old way of measuring the speed of the ship with a sandglass and knotted rope. It is said that Christopher Columbus made all his long voyages with only one 'clock' on board—a half-hour sandglass! Someone must have kept constant and careful watch on it to measure time. Today, if you want to boil an egg for three minutes and you have an egg-timer or threeminute sandglass, you cannot really go wrong. Start the sand 'clock' as soon as you have dropped the egg into boiling water on the fire. When the sand has run through from one glass vessel to the other, the egg is hardboiled. But if you are impatient and do not wait for the sand to run right through, you will have to eat a rather 'gooey' egg. If, on the other hand, the egg keeps boiling after the sandglass has run through, you will have to chew a very hard-boiled egg indeed! Some popular indoor games too use sandglasses to set a time limit. A watch would, no doubt, be more accurate, but a sandglass 50

is an easy and interesting way of keeping track of the minutes. The Chinese adopted a rather peculiar and laborious way of telling time. They knotted a rope at equal distances. This rope was wetted and set alight at one end. The time taken by the fire to reach from one knot to the next marked a unit of time! King Alfred spent much of his life fighting off the Danes from England. He probably needed to know the time often during his campaigns. In fact, he was the first person outside China to use the fire technique in 870 a.d. to measure the minutes, though in his own way. He invented a 'candlestick clock' which had notches marked down the entire length of the candle. It was placed inside a wooden lantern to protect it from any gusts of wind. King Alfred estimated that the candle took exactly four hours to burn down completely. If it were half burned, it meant that two hours had elapsed. The smaller markings on the candle, three for every hour, gave smaller indications of time as the candle burned from notch to notch. When it had burned out completely, another candle was lit at once, so the 'clock' ran continuously. You can well imagine King Alfred spending long hours keeping vigil against enemy attacks, by watching his clock burn steadily in the dark. All this while, even as people devised the 51

1

Candlestick clock—candle is marked in hours

strangest ways to tell time, others were trying to know more and more about the large number of stars in the sky every night. The science of astronomy was gradually developed through the study of stars and planets. A new way of telling time, by following star movements and patterns closely in the sky, was discovered. The Pole Star or Polaris was noticed to remain constantly above the North Pole. The earth's axis of rotation pointed northwards towards it. Polaris seemed to remain almost still in the sky while everything else revolved around it once in 24 hours. Star watchers used two of the stars in the Plough constellation as 'Pointers'. These seemed to travel round Polaris once in 24 hours. It was logical that time intervals could be measured by noting how much the Pointers had moved. In fact, any star could be used in this way on a dark and clear night. In those faraway days, instruments called 'nocturnals' were developed to help tell the time through stars.

AUtl

Garden sundial

It was not till much later, around the thirteenth century, that the mechanical clock was invented. Till that happened, people relied on devices like water-clocks, sundials and 'nocturnals' to measure the passing of the hours. However, these were not accurate timekeepers and were inconvenient to use because of their bulk and immovability. 52

With the invention of the ingenious mechanical clock, keeping time started to become really accurate and more simplified. 53

The Clock Goes Tick-Tock It was a wintry morning in Pisa, Italy, in the sixteenth century. A young student of seventeen years sat motionless in the Pisa cathedral. He looked worried and unhappy, and hardly glanced at the book of psalm that lay in his hands. He was in a dilemma. He wanted to study mathematics, his first love. His father insisted that he study medicine. He had little interest in the subject, although he had already started studying it at the University of Pisa. His father was, indeed, difficult to disobey! As the lad pondered over his problems, his gaze shifted to the high ceiling of the cathedral. Some repair work was being carried out there, and a lantern swung to and fro. He began to watch it with interest as it swung in wide arcs. Suddenly, his eyes widened. The arcs were becoming smaller 54

J

Galileo Galilei (1564-1642)

and smaller, but big or small, they seemed to take the same amount of time to swing. It was strange indeed! Galileo, for that was the lad's name, sat up straight in excitement, and felt his pulse. Its regular beat was his best time-keeper, and he began to time the lantern's swings. He was right. The lantern always required the same amount of time to complete a swing, no matter how long the range of its swing. Galileo did things thoroughly. He ran home in excitement to try out his own experiments. He fixed one end of a string to the branch of a big tree in his garden. He hung an iron weight from its other end. He now pulled the string back and released it. He had made a simple pendulum, like the lantern in the church. He next replaced the iron weight with a much lighter wooden one. This too took the same amount of time to swing to and fro, in a regular motion. Galileo thought hard. His experiment confirmed that the time taken for one swing remained the same, regardless of the weight attached. However, the time taken for the pendulum to swing did vary according to the length of the string. Galileo, who later went on to study mathematics and become a famous scientist, had discovered the laws of the pendulum. This early experiment made him realize later that the pendulum, which was a weight fixed to a 56

I v ;;

rod or .cord, could be used to regulate the movements of a clock once it was put in motion. After all, it had the astonishingly useful habit of swinging to and fro at the same speed according to its length. However, seven decades passed before a Dutch scientist, Christian Huygens, adopted Galileo's idea to build the first pendulum clock with a regulating movement. Galileo's remarkable discovery ushered in the era of accurate timekeeping. However, the first mechanical clocks had already appeared a few centuries earlier. Although it is difficult to say exactly when, water-clocks with moving parts were in use in China 500 years before, as we earlier saw. Around the thirteenth century A.D. the first mechanical clocks appeared in monasteries in Europe, and were operated by monks. They were enormous structures, often weighing several tonnes, and were made by unknown ironsmiths. These early contraptions did not have hands or a dial. They did not even strike the hour. They were used to alert somebody or to toll a bell that called monks to prayer. Their movements were simple and noisy, driven as they were by weights and wheels. Called 'turret clocks', these first clocks were nearly always placed on church or bell towers, so that everybody could see or at least hear them in the town. They were not of much use when they were out of sight or earshot for 57

The pendulum escapement

German rack clock

German novelty clock

anybody who wanted to move about and still know the time. However, despite their crude working, they managed to work for many years, although they did not always tell the correct time! The word 'clock' or 'clok' as it was called in Middle English, goes back to this time. It was taken from the French word cloche which means a bell. French was widely spoken by the English upper classes, and many English words were 'borrowed' from it. Bells were, therefore, associated with clocks in those early days of mechanical timekeeping. In fact, even before mechanical clocks existed, churches and monasteries rang bells to tell the common folk that it was time for prayers. The devout would stop all their activities, to say their prayers. Some of these prayers for which bells were rung were called sexts and nones. These terms were taken from Latin, and meant the sixth hour and the ninth hour, when prayers were said. So the ringing of prayer bells also indicated the time. Even when mechanical clocks with dials and hour hands were made they struck the hours and were used in the same way as prayer bells. So it is little wonder that all timekeepers were called clocks or cloches. The French themselves, strangely enough, call a clock horloge, which has nothing to do with bells but indicates 'hours'. 58

From the beginning, these clocks were designed to tell the time by dividing the day into 24 equal hours. This was based on the ancient Egyptian time division of one day. The hours were further divided into two lots of 12 hours each for every day, that is, 12 hours of daytime and 12 hours of night. However, we really do not know why the divisions fell in the middle of the day and the night—falling after noon and after midnight. People had further divided each hour into 60 minutes, and each minute into 60 seconds. The figure 60 was probably taken from the ancient Babylonian counting system which used 60 in much the same way as we use 10. However, the earlier mechanical clocks did not bother about marking smaller divisions for minutes on their dials, or using a minute hand. This was just as well, considering that they were not very accurate anyway! Some of these early clocks still exist. The oldest surviving clock in England is at the Salisbury Cathedral, and is over 500 years old. It has an ornate dial, with 24 hours marked on its face in two lots of 12 hours each. This clock struck the hours. The mechanical clock was indeed a big leap from the age of sundials and sandglasses. It worked in a rather clever way. A weight was attached to a cord wrapped around a drum. As the weight hung down, the cord unwound, turning the drum. This in turn moved a series 59

Rolling clock from the 17th century

Falling ball clock of the 17th century

American acorn clock made about 1850

of toothed wheels or gears. The wheels turned a pointing hand on the dial to tell the hour. This does sound easy enough, but in actual practice, it was quite difficult to make. This was because the hand had to move steadily and go right round a circle once in every 12 hours, without changing speed. For this, a mechanism called an 'escape wheel' was later provided, which served as a kind of brake. This prevented the hour hand from whizzing around the dial. Although these clocks were most useful, they did lose at least half an hour everyday. So we cannot say that they were very reliable timekeepers. Luckily there were no trains or aeroplanes to catch in those days! It is likely that the speed at which the parts of these clocks moved was altered slightly by hot or cold weather, as also by oiling or rusting of these parts. Late in the fourteenth century, the first clocks appeared in homes. They were simply smaller versions of these large public clocks, and were rather plain structures, with no protective cases. They usually stood on a pedestal which had an opening to accommodate their weights. These domestic clocks must have taken pride of place in the homes that possessed them. You can imagine how their owners probably invited much envy! For they could now see the time at home always—rather than 60

having to rush out every time to the public clock, in rain or hail, to see if the school bell was about to ring! Do you know that many of the things we take for granted today began as great luxuries? When you were much younger, you must have had a few, favourite clockwork toys to play with, which you wound with a key or knob. Once these were wound and set down, remember how the clockwork mouse ran or the train moved with a loud whirr! You might have even had a musical box that played a gay tune once it was wound. All these simple, mechanical toys are driven by clockwork. They are provided with a coiled

Portable clock

spring, which is a thin steel ribbon that bends to form a tight coil when you wind it. When released, the spring begins to uncoil and turns gear wheels, which in turn drive a spindle or axle around. This makes the toys move or play. You may be wondering what all this has to do with clocks or with time. Actually, many clocks and watches are powered by coil springs in much the same way as clockwork toys. It was at the beginning of the sixteenth century that the first spring-driven clocks were made. Peter Henlein, a German locksmith, had the ingenious idea of ridding clocks of their heavy weights which made them impossible to carry or shift around. He began to make small clocks that measured four or five inches in diameter and about three inches in depth. These were the first portable timepieces, carried by hand, and represented one of the greatest strides in the history of timekeeping. The secret of these 'travelling timepieces' was that they were driven by a spring instead of by weights. Just as weights in a clock made the drum turn around, so the coiled spring made the wheel turn round. In principle, they worked in just the same way. A difficulty did crop up with these early spring-powered clocks. In a weight-driven clock, the driving weight always remained the same. However, if you have seen a spring unwind, you will notice that it pulls much 62

faster when it is fully wound than when it has nearly uncoiled. This irregular movement would make the clock move unsteadily too. However, in about 1525 A.D., a Swiss clockmaker overcame this rather serious defect by inventing the 'fuses'. This was a clever arrangement which used a spiralshaped drum to regulate the movement of the spring. Those portable clocks had dials placed on their uppermost sides. They possessed an hour hand, and were exposed to the air. Their mechanisms were made wholly of iron. Later brass was used, and steel for the more delicate pieces. It was only later, in the seventeenth century, that glass covers were made, and the mechanism enclosed in brass cases. The clock began to have a profound effect on society as people became conscious of time. It was not long before watches evolved from portable clocks, in the sixteenth century itself. At first, these were hung on belts or worn round the neck. By the next century, it had become most fashionable in Europe to carry a pocket watch or 'watch fob', as it was called. This was a short ribbon or chain attached to a watch which hung out of the pocket in which the watch was kept. Later, the more watches one carried in waistcoat fob pockets, the more fashionable one was considered! Right till world war the first and the development of wristwatches, watches for 63

Pocket watch

Grandfather clock

men had, in fact, to be carried about in pockets. Galileo had prepared the way for the invention of the modern clock with his discovery of the laws of the pendulum. The spring-driven clock or watch used a 'verge' which depended for its accuracy on being pushed with the same force all the time. Lots of little things like heat and cold of the day could affect its regular working. Christian Huygens used the pendulum as the time controller in clocks, instead of the verge. After all, the regular movement of the pendulum would not be affected by small changes in the pull of the spring. The idea worked, and suddenly there was a great demand for clocks. Clocks were made with short pendulums to hang on walls.The next step was to enclose the pendulum and weights, and the long case or stately 'grandfather clock' was born! The pendulum commonly used in clocks, a cord or a chain, has an 'escapement' device which gives small, regular pushes to the pendulum to keep it swinging. Each time the pendulum swings aside, one tooth of a gear wheel turns past the escapement. This takes exactly one second in many grandfather clocks, and produces the familiar 'tick-tock'. Most grandfather clocks tell the time not only by hour, minute and second hands, they also have a deep chime. They usually chime every 15 minutes, with a different chime. 64

On the hour they chime the number of hours. These chimes are triggered off when cogs in the clockwork mechanism go past a certain point. Clocks became more and more decorative. In fact, clockmaking became a specialized craft. Skilled workers migrated from country to country, as watchmaking and clockmaking became an international trade. Cuckoo clocks which sung out the time to the call of a 'cuckoo' arrived! Although the pendulum made clocks more accurate, it could not be used for watches. A pendulum works only if it hangs straight, and not if it lies on its side, nor if it is moved around. Watches that told the correct time were developed with the help of two new inventions—the hairspring and the lever escapement. They are still commonly used in millions of clocks and watches today, despite the modern technology of our newest timepieces.

Cuckoo clock

65

Time Moves On Industrialization, which began in the eighteenth century, changed the face of the globe. With the use of new materials like iron and steel, new energy sources, and the invention of many remarkable machines that increased production, the world became a much more complex place. Suddenly, old leisurely ways of life were gone. Important developments in transport and communication like the steamship, the automobile, the airplane, radio and telegraph made it more urgent than ever to live life according to the clock. All this while, the clock had been used for the most ordinary purposes—like getting to school or to work on time, or catching a train. It did not need to be accurate to within more than half a minute or so for these everyday things.

With the twentieth century, time had to be much more exact. After all, it had to keep pace with the new science and technology that was sweeping the modern world. Accuracy no longer meant keeping time to the half minute or even second. Even one-hundredth of a second mattered in fields like astronomy! Timekeeping had already become a science with the introduction of chronometers for sailors in the eighteenth century. These gave the right time to within a very few seconds. It was indeed a matter of life and death to have good clocks on board the ships. In the olden days, even for long sea voyages, there were only crude instruments and rough tables to find positions at sea. There were no proper clocks. Many a ship was wrecked and sailor drowned because of unknown locations, as there were no reliable clocks. As your geography book must have told you, the intersection of latitude and longitude gives the exact position of any place. Sailors could figure the latitude they were in, by measuring the position of the Pole Star. However, to find their longitude, they needed the exact time. Realizing the gravity of the problem, the British Admiralty offered a prize of 20,000 pounds to anyone who made a reliable clock that worked well at sea. It was a challenge. John Harrison was a carpenter, but a genius with clocks. At that time, the hairspring and lever escapement had not been invented. 67

John Harrison (1693-1776)

Chronometer

He set to work to design a clock with a kind of pendulum that would keep accurate time through rough sea passages and changes of temperature. After much painstaking effort, he succeeded in making unbelievably accurate clocks which were better than some of our modern watches. The chronometer, which he made in 1760, after many years of experiments, showed an error of only 15 seconds in five months! Harrison's clocks are still working. They are kept in the National Maritime Museum at Greenwich. It was a long time before anybody could improve on them, for they were so good. Unfortunately, the prize money was given to him with the greatest reluctance. He was merely given small sums to carry on his work. It is a sad story that Harrison was an old man by the time he received half the prize. And it was not till matter was taken up by the King and Parliament that he received the full amount. By the nineteenth century, shipping was growing in importance because of increased trade and transport. Chronometers became readily available for ships. They were mounted in a special brackets to keep them level on a rolling sea. They were cheap and accurate timekeepers, and made the seas safer for mariners. Meanwhile, pocket watches were being fitted into specially made bracelets or leather 68

straps. Women began to wear them like pieces of jewellery. Wristwatches became popular with men with the first world war, when soldiers found it difficult to reach inside bulky uniform jackets to check the time. All kinds of clever, new ideas were now coming up for timepieces. Today, we use mainly three types of clocks and watches—mechanical, electrical and electronic. Mechanical clocks and watches are spring-driven, electric clocks are powered by electricity and electronic ones are quartzbased. Although these are accurate timekeepers, they can gain or lose time if run continuously. Most mechanical watches have to be wound every day by hand. Some are self-winding. They contain a swinging weight which is geared to the coiled mainspring. When you move your hand, the weight turns and winds the spring. So you need not bother about winding. This ordinary watch is really a complicated bit of mechanism, containing about 211 different parts. It is powered by its mainspring which is about two feet long when straightened out. When you wind the watch, you tighten the coil of the mainspring, rather like a clockwork toy. ^ , . .1 Spring-driven clock From the mainspring, the power travels 1 . winding key 2. Mainspring through a series of four wheels, called the | Cerrtrewhee. 4. ^cape^wheei 'train' to the delicate balance wheel. The train 7. Balance wheel 69

moves the hands on the dial while the balance wheel, the heart of the watch, regulates its movements. It acts like the pendulum of a clock, and spins back and forth steadily. The hairspring, a coiled steel wire, no thicker than a hair, lies inside the balance wheel. Around the balance wheel, tiny screws of gold or steel control the speed of the watch by their position and weight. An escapement wheel regulates the movement of the balance wheel. This is the sound that causes a watch to tick. The wheels in the watch rest on pivots which are in constant friction. To withstand this, the pivots rest on tiny bits of precious stones like ruby, garnet or sapphire, which are next only to diamonds in hardness. These are called the Electric clock 'jewels' of a watch, and their number is inscribed on its outer case or dial. More jewels mean less friction to wear out or slow down moving parts in the watch. So it is an indication of quality. Ever since man knew enough about MERCURY CELL electricity to make use of its power, he tried to apply it to clocks and watches. The simplest way to do this, he found, is to have electric currents replace the weight or spring as a source of power. Most electric clocks are driven from the ordinary mains supply, which BALANCE is called 'alternating current'. Usually, the WHEEL current flowing in wires changes direction Inside of an electric clock exactly 50 times a second. This keeps clocks 70

correct without any regulation. Of course, one must beware of power cuts or even voltage fluctuations! Electronic watches are most popular today. They have batteries to power them. They are regulated not by a spinning balance wheel, but by a vibrating tuning fork. Battery-operated electromagnets set off the vibrations, which are passed on to the gear-wheels, to move the hands of the watch. More recently, nature has been tapped to discover a most accurate tuning fork—a quartz crystal. It has been discovered that when an electric current is passed through a quartz crystal in little waves, the crystal vibrates at a special speed—32,768 times a second. Clocks and watches regulated by electric impulses with a crystal are amazingly accurate to a second in fifty years! Man has made an even more astounding discovery! He has dug deeper into nature to use the very smallest particles of matter called atoms. Since the 1940s, scientists knew that the electrons of atoms oscillate with a rhythm so regular that they could be used to tell time. Thus, a very sophisticated clock known as the 'atomic' clock has been developed, which allows the astonishing splitting of seconds. These clocks generally use atoms of caesium, a silvery-white metal. Some of the latest ones are so precise that they gain or lose less than one second in 30,000 years! 71

The front of a quartz crystal clock

The back view

An atomic clock

Atomic clocks are being used as a standard of time at some 50 timekeeping stations round the world. They are also being used in sophisticated navigation systems and space communications. They have ushered in a new era in the field of time measurement. Indeed, they are better timekeepers than our earth itself! Different countries specialize in making different kinds of clocks. Britain has long been famous for its chronometers as also chimeclock movements. The chimes of the world's most famous clock, Big Ben, in London, have been broadcast live for decades by the BBC. The Black Forest of Germany was famed for its beautiful cuckoo clocks, handcarved in wood. Watchmaking has been a national industry in Switzerland, ever since the appearance of the wristwatch. In fact the Swiss always led in the production of high grade watches. Special feature watches such as alarms, calendars, automatics and chronographs were made almost exclusively in Switzerland. Today, over half a billion watches pour out of the world's assembly lines every year. Japan's Seiko group is the world's largest timepiece manufacturer. In a 1.8 hectare plant, 1,200 robots screw parts into inexpensive quartz crystal watches. Every two seconds a new watch—standard or digital—pops off the assembly line! 72

Nature too has its clocks. Fifty years ago, an American chemist, Willard Libby, found a natural timekeeper in everything that had existed in the last 50,000 years. This was the carbon-14 atom, which decays at a known rate. Scientists can now tell the age of an Egyptian mummy or a fossil by determining their levels of carbon-14. Relics too could be dated to give history more accurate dates. What is more, there are natural cycles within our bodies that can perceive time all on their own. If you were stranded on an island with no clocks around, your body would fall naturally into a 24-hour pattern of sleep and wakefulness, with meals thrown in at regular intervals. This is the body's clock it work. Biologists call it the 'circadian rhythm'. If we break this rhythm for any period of time, many disorders in the body can result. If you have been on a long flight across several time zones, you will know what 'jet lag' means. You feel groggy and out of sorts. It usually takes the body many days to readjust to a new daynight pattern.

73

Radioactive clock—the age of some elements like carbon is measured by their decay. It takes 100 million years for the part A to decay; another 100 million years for part B and another 100 million years for part C.

A Calendar

The Great Calendar Stone

A world without clocks would surely be a topsy-turvy place. Imagine what a world without calendars would be like! There would be no way of keeping track of the weeks, months or years as they went past, or of anything else, for that matter. You would not have the foggiest notion of how old you were. At school you would not be promoted after a year, but would probably sit in the same class always! No birthday parties, no festivals, not even plans for vacation—after all, these are all measured by a calendar. What a muddle everything would be! Did you know the word 'calendar' comes from calendarium, the Latin word for 'account book'? It means the division of the year, like a set of accounts, into days, weeks and months. A calendar does indeed regulate all our affairs—at home, at work, even in the fields, 74

and it also reckons time for religious and scientific purposes. Calendars have been around a long while. We saw how man found ways to measure time long before he had invented any instruments to do so. Early in history, he began counting time by days, months and seasons, which were all natural time units. He thus had the first beginnings of a calendar. Ancient tribes used a dawn-to-dawn reckoning to count the days. They probably called a number of days so many 'dawns' or 'suns'. In those far-off days, there were no fancy calendars like the one you have hung up in your room to keep track of the year. They simply used sticks with crude notches in them to count the days, or strings with knots in them to keep a record of so many full moons or even seasons. These were really our earliest calendars. The calendars used by all ancient civilizations were based on natural phenomena, or units of time such as the day, month and year. Two kinds of calendars came into use— the 'solar' calendar which was based on the earth's revolution round the sun, and the 'lunar' calendar, which was based on the movements of the moon. When you come to think of it, the intelligence of our ancients truly laid the foundation for our way of life today! Like many other things, the story of the calendar began in the great civilizations that 75

Australian memory sticks

The Incas of South America used knotted ropes known as 'quipu' to remember things.

awakened nearly 5,000 years ago along the life-giving rivers of the Middle East—in Sumer, between the Tigris and the Euphrates, and in Egypt, along the Nile. The ancient Egyptians introduced the use of a practical calendar in 4,200 B.C. They were the first people to measure the year with some exactness, although their first estimate was not quite right. They started with a lunar (monthly) calendar based on the appearance of the new moon every 29 or 30 days. As one year had 12 months, they calculated that this would give them a year of 360 days. It was a round figure that would have been most convenient for calendar-making, but as the Egyptians cleverly discovered, it was not very accurate. The annual flooding of the river Nile on its surrounding banks was most important to Egyptian farmers, for it brought renewed fertility to the land. Egyptian astronomers began to time this important event, which was celebrated as the ancient Egyptian New Year. They were observant men. They noticed that this flooding occurred every year when Sirius, the bright Dog Star, An ancient Egyptian calendar—the 12 months are shown as discs.

first appeared in the early morning sky before sunrise. The annual morning appearances of Sirius had an interval that was a few days longer than the 360-day Egyptian year. The puzzled astronomers probably scratched their heads and mused. It was obvious that their year was a little short. Their scientific calculations were better, based on the more accurate 365-day solar year. The answer lay in extending the old year by adding on an extra five days. This was done at the end of the year, and the extra days were set aside for feasting and revelry during the Nile's annual government and administration. However, old habits die hard, and everyday life was still based on the old lunar year. So things remained. Soon, even the 365-day year was seen to be inadequate. Astronomers calculated that there were six hours missing in a year. The knowledge of the scholars of this period must indeed have been tremendous! It was around 240 B.C. that Ptolemy III, King of Egypt, tried earnestly to set the calendar right by adding an extra year every four years. He had come very close to finding the right solution—but alas, it was not to be! The powerful clergy refused to accept his 'leap year' which would change their long calculations and the dates of all religious festivals, which were based on the old 77

Julius Caesar (100 B.C.-44 B.C.)

Mayan calendar

calendars. This same leap year was adopted 200 years later by the Roman General and ruler, Julius Caesar. Another highly developed civilization flourished in Central America, quite cut off from the rest of the world. The Mayas here worked out their own time scale with astonishing accuracy. Their early astronomers achieved this by means of stars and planets. Their calendar used a 'year' based on the movements of the planet Venus which they studied closely. You can see it shine brightly in the western sky after sunset. The Mayan astronomers drew up a 'Venus year' which had 18 months of 20 days each. However, they realized that this 360-day year was not quite right, and added another five days to each year. These five extra days were considered to be unlucky. The Maya people made the most elaborate calendars which they carved on stone. Indeed, these heavily worked stones with pictures and hieroglyphics 3,000 years old are the pages of their calendars for us to see even today. These calendars were very complicated, however, and their clumsy system of counting only made matters more difficult. Unfortunately, we do not know very much about this ancient civilization which was destroyed. The Babylonians and the Greek had their own calendars too. Studies of cuneiform tablets found in Mesopotamia show that its people 78

f

I

reckoned time as far back as 2700 B.C., somewhere near the invention of writing. Like the Egyptians, the ancient Babylonians were drawn to the movements of the stars and the changing seasons. They developed a year of 360 days, and divided it into 12 lunar months of 30 days each. However, their astronomers soon realized that this year was short by about five days. In six years, this difference would add up to 30 days or a full month! They solved the problem by adding on a thirteenth month after every six years. The calendar which we, along with the rest of the world, use today came from the early Romans. They also gave us the names of the months of the year. It may surprise you to know that this calendar was not as simple as it seems, but was arrived at after a long process of trial and error. This took many many centuries, involved several famous personalities, and led to fierce arguments, even riots! Ultimately, the present day Gregorian calendar as it is called, was designed, accurate to a day in every 3,323 years! The Romans were a powerful force that ruled over much of the known world at the height of their might. Wherever they went, the influence of their rich culture—the Roman alphabet, numerals and even their calendar— was adopted by different people, far and wide. When the Romans first took their calendar 79

from the Greeks, it had a year of only 304 days, divided into ten months beginning with March. The last month of December was followed by an uncounted winter gap. In fact, right till the reign of Julius Caesar, the calendar was flexible and followed no hard and fast rules. Rulers lengthened or shortened months at will. If somebody important wanted more time to complete a project, he merely made the month longer! Students must have dreamt of lengthening the vacation months! Ultimately, the calendar was changed so often that it became hopelessly confusing and meaningless, for business or administration.

Janus

A king of Rome called Numa Pompilus is believed to have added the months of January and February around 700 B.C., since the tenmonth year was much too short. They were attached to the end of the year in the uncounted winter gap, and were the new eleventh and twelfth months. January took its name from Janus, a two-headed Roman god who was believed to guard doors and gates. One of his heads was said to turn back to the past, the other towards the future. February derived its name from the Latin 'Februarius' which means 'to purify'. The ancient Romans traditionally held a festival of purification in February, the twelfth month, to prepare for the next year. The name stuck even after the month was shifted from twelfth to second place in the calendar. 80

This new calendar was more accurate, but still not good enough for it was only 355 days long. By Julius Caesar's reign, the dates were three months ahead of the seasons. It is like having Christmas fall in the spring, or Holi in middle of the rains! Julius Caesar took a major step to rearrange the old calendar into something better. He acted on the advice of a Greek astronomer called Sosigenes, and the 'Julian calendar' was drawn up in his honour. This was a immense improvement on anything that had been used before, and was used for 1,500 years. This calendar was based on the time taken by the earth to complete one revolution round the sun, that is, the solar year of 3651/4 days. Sosigenes realized that the ordinary year must have an exact number of days to be practical. Any leftover hours would become most awkward. He decided on a year of 365 days with an extra day added at the end of every four years to correct the error. The extra long years became known as leap years. The number of months remained at twelve, but since 365 is not exactly divisible by twelve, they could not all be of the same length. Various changes were made in the calendar to make the months longer, so as to make the calendar just right. We saw how January was originally the eleventh month, with only 29 days. Caesar 81

A page from a Medieval Christian calendar

pushed it to become the first month of the year with 31 days. March, May, July, October and December were also given 31 days each, while the others had 30 days. However, when the New Year was shifted to January 1, the names of the other months were not shifted. So we see a difference in the meanings of certain months and their order of appearance in the year. For instance, September comes from 'septem' meaning the number seven, but its position in the year is ninth. October means 'octo' or eight but it is really the tenth month. Similarly, November is from 'novem' or nine, but it comes in at number eleven. December's old name has stuck as well, for it is named after 'deka' or ten, but is really the twelfth month of the year. The Romans never bothered to alter these names. Julius Caesar is remembered for something else as well. He renamed the fifth month of the earlier calendar, Quintilis, after himself. It is called July since then and was given 31 days in his honour. Caesar 'borrowed' one day from February to do this, so February was left with only 29 days. In a leap year, it was reasonable to attach the extra day to February to give it 30 days. It was brought forward too, to become the year's second month instead of the twelfth. The Romans named many of the other months after gods and goddesses. March, with its squalls and gusty winds, was named after Mars, the Roman God of War. He was also the 82

God of Farming, and was worshipped in March when the fields were made ready for sowing. It was in March too that the Romans could prepare themselves for battle again after their long, cold winter. The Goddess Maia, daughter of mighty Atlas who was believed to carry the world on his shoulders, gave her name to the month of May. It is likely that June got its name from the Goddess Juno, wife of Jupiter and queen of the heavens, who rode a chariot drawn by peacocks. Ancient Rome celebrated a festival in her honour at the beginning of this month. When a new emperor came to the throne, he liked to change many things to assert his importance. So it was with Emperor Augustus, grand nephew of Caesar, who came to the throne when the latter was murdered. It was important to him to have a month named after himself, so he renamed the old month Sextilis as 'August' after himself. Now August had only 30 days—a day less than July. Augustus objected strongly, and so another day was taken from February and added to August to make it equal to July—Caesar's month! February was thus left with only 28 days, except in leap years when it had 29, while August had 31. All this juggling really did muddle up the entire arrangement! It made three 31-day months (July, August and September) appear in succession. So Augustus thought hard and 83

Roman Emperor Augustus (63 b.C.-A.D. 14)

made more changes. He reduced September to 30 days, added a day to October to increase it to 31 days, reduced November by one day to 30 days and finally increased December from 30 to 31 days. The important thing was to have an accurate calendar of 365 days. It does seem extremely strange to us today that a calendar which was used all over Europe could be changed just to flatter an Emperor of Rome. However, we still follow the same 365-day calendar, and its sequence of months with their lengths remain unchanged even today. Has it ever happened to you that a small mistake grew bigger and bigger till it became quite serious? This is what happened with the Julian calendar, which seemed accurate enough to begin with. However, even after leap years had been added, things were not quite right, for the calendar year now became long by 11 minutes and 14 seconds. This was because the earth actually takes 365.2422 days to complete one revolution of the sun. The correction of a full day every four years was, therefore, a little too much, and this error added up to a full day in 128 years. The earth's year is 365 days 5 hours 48 minutes and 46 seconds.

By the sixteenth century, the Julian year was ten days behind the solar year. Catholics grew terribly concerned about the calendar's inaccuracy. It meant that Easter would gradually shift from being a springtime festival into a winter one! For a long time, people clamoured for some kind of reform. Ultimately in 1582, Pope Gregory XIII decided to correct matters. On the advice of astronomer Clavius, he issued a decree which stated that instead of having 100 leap years in every 400 years (one every four years), there would be only 97. How would this be done, since every year exactly divisible by four should be a leap year? Pope Gregory declared that the century years (1600, 1700, 1800 and so on) would be regarded as leap years only if they were divisible by 400. As you can calculate, 1600 and 2000 are leap years, but 1700, 1800 and 1900 are not, and February has only 28 days in all these years. This settled matters very well, for the error in the Gregorian calendar was reduced to merely 26 seconds per year, or one day in the next 3,323 years! But the problem of the extra days still remained. Pope Gregory's solution was to drop ten days from the calendar, so that October 4, 1582, was followed straightaway by October 15,1582, to bring everything back to its correct timing. 85

Astronomical years

Gregorian years

A year of 365 days is a quarter-day short of the astronomical year. Adding an extra day every fourth year brings the calendar into step.

All Catholic countries agreed to adopt the new calendar—after all, the Pope was the Head of the Roman Church and nobody dared disobey him. Britain was Protestant, and kept using the Julian calendar for almost another century. By then, the error had increased to eleven days. Their Parliament finally passed an Act recommending that the use of the Gregorian calendar. September 2 was to be followed by September 14. The dates in between would really vanish into thin air! Strangely enough, many people reacted very strongly to this change. They felt angry and cheated out of eleven days. Maybe some of them would miss birthdays or other important events! There was rioting in London and supporters of the Gregorian system were attacked by enraged mobs. However, the anger finally died out. Today, all countries use the Gregorian calendar. Russia was the last country in Europe to adopt it after 1917 when the erstwhile U.S.S.R. was created. It is wiser to keep time with the rest of the world, is it not?

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Calendars The World Over It is difficult to discard old ways altogether, especially if they hold some special meaning. Although everybody uses the Gregorian calendar, some countries still have other kinds of calendars, which they have been traditionally following from ancient times. The Muslim calendar, has been retained by most Arab countries, while the old Hindu and Jewish calendars continue to be used for religious purposes. So certain countries or religions really follow two different calendars, which can be confusing at times. Some newspapers in these countries print their dates according to both the calendars in use. The Gregorian calendar, as we saw, is a solar calendar (based on the earth's journey round the sun, which takes a little over 365 days). Another calendar people consult is the lunar calendar (based on the movement of the 87

A Muslim calendar of 1787

Ancient Egyptian temple calendar

moon). This was popularly used in the ancient world, and the traditional Hindu, Muslim and Chinese calendars are still based on it. Since the moon takes 29.5 days to complete one revolution of the earth, it takes 354 days for 12 such revolutions. The lunar year of 354 is 11 days shorter than the solar year. In three years this difference grows to a whopping 33 days! To keep the lunar year in step with the solar year, this difficulty is solved by making every third lunar year consist of 13 months. We call this additional month malmas in Hindi. Every calendar welcomes the first day of the year as the New Year. This is one of the oldest and gayest customs of mankind, and is celebrated the world over. New Year's day is a great time for parties and reunions that ring out the old year and ring in the new one. It is a time to make New Year 'resolutions' as well, though these are soon forgotten! In the bigger cities of the world, many people collect in a big square to welcome the New Year. They greet each other and embrace each other. In London, Trafalgar Square is the traditional gathering place, while Times Square is popular in New York. In fact, no festival has been celebrated in such a variety of ways and on so many different dates according to the calendars used by different countries or religions. We do not really know how New Year 89

celebrations first began. Some believe that the Chinese were the first people to start them, others claim that it was the ancient Germans, while still others say that it was the Romans. The Chinese celebrate two New Year days. One is on January 1, which is New Year's day according to the Gregorian calendar. Their other day is reckoned by the Chinese lunar calendar, and can fall any time between January 21 and February 19. During this time, there is a gay festival which lasts several days. It is a time too for family get-togethers over lavish meals. Children look forward eagerly to this happy festival, for they are given 'good luck' money in red packets. Indonesia also has two celebrations—on January 1, and on the Islamic New Year, a date that varies from year to year. The Russian Orthodox Church observes the New Year according to the Julian calendar which places the day on January 1. 'Rosh Hashananah' is the Jewish New Year, celebrated about the time of the autumnal equinox at the end of September or beginning of October. In Vietnam, the New Year usually begins in February. The Koreans celebrate their New Year during the first three days of January, while Iran celebrates it on March 21. The people of Morocco observe the beginning of the year on the tenth day of Muharram which is the first month of the Islamic year. 90

The ancient Greeks began their New Year with the new moon after June 21. The Roman New Year was celebrated on March 1, till Caesar changed it to January 1, according to the new Julian calendar. It is said that the ancient Germans established a New Year festival because of the changing seasons. The German winter set in around mid-November, when they gathered the harvest. It was a happy occasion when everybody got together at the end of a time of hard work in the fields. They looked forward to a period of rest from work in the cold, long winter ahead, and so made merry. Even though it was only November, they considered it the beginning of a new year! In most Christian countries, the new year now begins on January 1. In the Middle Ages however, one calendar was used throughout much of Europe in which each new year began on April 1. So it was celebrated as New Year's day. People exchanged gifts and visited friends. Being the beginning of springtime as well, celebration was in the air. In the sixteenth century, it is said that Charles X, King of France, ordered people to adopt the new reformed calendar where the year began with January 1. Although most people agreed to do this, there were some stubborn ones who refused to change. They continued to celebrate April 1 as New Year's day, and so became the butt of jokes and tricks 91

Charles X (1759-1836)

Lunar calendar—12 lunar months are 11 days short of a year.

by their friends and neighbours! They sent them on fools' errands, made them gifts, invited them to parties that were not held and generally played lots of tricks on them on the day. These people became known as April Fools, and April 1 became April Fool's Day. This became a day for practical jokes all over the world. April Fool's Day is probably one of the most enjoyable days in school, for you have a good excuse to play the fool without fear of punishment! In India, each religious group has its own date for beginning the year. In fact, around thirty different calendars exist! Some are lunar, some solar, while others are based on religion or even astrology. You can imagine what a great muddle our dates would be in, if all these calendars were to be used! In 1957, the Indian Government found a way out. It introduced the Saka calendar as the official calendar, and stated that only this would be used along with the Gregorian calendar. The Saka or Indian national calendar is based on the lunar system, but the days of this calendar correspond permanently with the Gregorian calendar. Chaitra, which is the first month of the year, falls on March 21 every year, and on March 22 in a leap year. This is the Hindu New Year. The Sakas, incidentally, were the first invaders from Central Asia who established two dynasties in north-west India. Chastana 92

was the founder of the second dynasty in 78 A.D. which marked the beginning of the Saka era. This lasted for almost three centuries till they fought the powerful emperor, Chandragupta Vikramaditya, who defeated and killed the Saka king in 388 A.D. Since then the Saka calendar began its count from 78 A.D. The Indian national calendar lags 78 years behind the Christian era. So if you are born in 1982, according to the Indian calendar your date of birth falls in 1904! How do you celebrate the New Year? Is it with a big bang, or do you sleep through the end of the old year, to wake up right into the new? It is a time for sending New Year cards to all those near and dear to you, with wishes for a happy year ahead. You even send cards to casual friends, and to most people you know. You probably receive piles of colourful New Year cards, to put on shelves or hang from ribbons and streamers. The custom of sending New Year cards is very old. Did you know that the Chinese have been doing it for more than 1,000 years? These cards carried the name of the visitor who came to call (for there was no postal system then!), but there were no greetings or messages on them. For people the world over, the coming of the New Year is a symbol of starting a new life with renewed hope for the future, and putting old troubles behind. That is why the New Year 93

Charlemagne of France (742-814)

has been greeted with joy everywhere down the ages, in the hope that it will bring in a good, new life. You maybe wondering when these different calendars actually count time from—for they certainly did not, start together. The time system we use in everyday life, the Gregorian calendar, begins its count with the birth of Christ. Everything before his time is marked B.C. (Before Christ). Your history book is full of dates with B.C. after them, which you probably know by heart. Everything after the birth of Christ is marked A.D. (Anno Domino or In the Year of our Lore). This practice of dating events from the birth of Christ came into general use only in the time of Emperor Charlemagne in the ninth century. A mistake was made then, which dated the birth of Christ five years later than it actually was. The Greeks dated their calendar from the Olympic Games which started in 776 B.C. The Romans counted time from the founding of their city in 753 B.C. by Romulus. The Muslims use a different calendar that begins its count from the flight of Prophet Mohammed from Mecca to Medina, the Hejira, in 622 A.D. Jewish reckoning goes back to the supposed year of creation which they calculated as having taken place 3,760 years and three months before the birth of Christ. As mentioned, the Indian national calendar based 94

on the Saka era begins in 78 A.D. All these dates are according to the Gregorian calendar. Once man had a calendar to organize his life, he felt the necessity of grouping days together into periods shorter than months, for his different activities. It was convenient to fix different days for marketing, trade, feasts and other activities. In the beginning, every tenth day was allotted to a certain task. At other places, one day after every five or seven days was fixed for such an activity. In Babylonia, every seventh day was treated as a special day. This was because of their belief in the sacredness of the number seven which was probably related to the seven planets. In ancient astronomy, the name 'planet' referred to the seven celestial bodies that were seen to move noticeably against the background of apparently 'fixed' stars. These included the Sun, the Moon as well as the five planets, Mercury, Venus, Mars, Jupiter and Saturn. In fact, a fixed day in the week was devoted to the worship of one of these planets, which were looked upon as gods. The Egyptians also adopted the seven-day system. They named the seven days after the five planets, and the sun and the moon which gave us the names of the first two days of the week—Sunday and Monday. Their other names were Mars day, Mercury day, Jupiter day, Venus day and Saturn day. 95

A wood calendar used in Tyrol from the late 17th century until the mid-19th century. Each plate represents one month.

By the first century B.C., the seven-day week had been adopted throughout the Roman world. The present names of the weekdays are taken from the Anglo-Saxon names of gods. The day named after the sun is Sunnandaeg or Sunday. The moon's day is Monandaeg or Monday. Similarly, the day named after the planet Mars is called Tiwesdaeg or Tuesday. It was the Norse god of War. The day named after Mercury is Wodendaeg or Wednesday. Jupiter's day is Thordaeg or Thursday, the day of Thor, the Thunder God. The day of Venus is Friggdaeg or Friday. It comes from Freya, wife of God Woden and mother of Thor. It is said that she was given a day so that she would not be jealous! Saturn's day is Saeterndaeg or Saturday, named after the Roman God, Saturn. One day of the week was kept for rest and prayer. This was traditionally Sunday for all Christians, while Jews rested on Saturday. This was the 'Sabbath/day. Incidentally, a day used to be counted as an interval between sunrise and sunset. The Romans counted it from midnight to midnight. This method is used almost everywhere. The calendar we use today is very accurate. However, it is not very symmetrical with its months of varying lengths. There have been suggestions to make a new 'World calendar' where the present months will remain the same but the days will be rearranged. This has been designed by 96

dividing the year into four quarters of 91 days each, with an additional day at the end of the year. The first month of each quarter has 31 days and the rest of the months, 30 days each. The additional day follows December 30 and does not belong to any month or week. Similarly, in the leap year, the extra day follows June 30 without being part of any month or week. In the World calendar, January 1, April 1, July 1 and October 1 all fall on Sundays. There are many advantages of such an arrangement. In the first place, it would save on printing new calendars every year, for dates would always fall on the same day of the week. If your birthday is on a Friday this year, it would always fall on a Friday. It would also be easier to work out school holidays, festivals and other occasions on definite dates for all time. In spite of these advantages, however, the idea of the World calendar has not become very popular. Perhaps this is because old habits die hard, and we are quite habituated to the existing one.

97

Crossing Time Zones Irina jumped up and down in excitement. She was going to meet Grandma who lived in faraway Vladivostock, by the Trans-Siberian Railway from Moscow. It would be a long, long journey of almost 10,000 km across the vast stretches of Siberia. And it would take seven whole days to reach! Grandma was a wonderful cook. She had promised to make plenty of delicious goodies for Irina when she came. No wonder she could hardly contain her excitement! The 'Russia Express', as the long train was called, travelled fast across the treeless plains of Siberia. Yet the journey seemed endless. It was very early in the morning— 5 o'clock according to Irina's watch, when 98

they reached Vladivostock at last. She was usually fast asleep at this hour. Was she not glad to be able to stretch her cramped legs! When Irina looked outside, she stared in surprise. The sun was shining right overhead, and Grandma was smiling at her on the platform. It was lunchtime in Vladivostock and Grandma had made lots and lots to eat! For the time was one o'clock. Irina just could not understand how time in Vladivostock was different. It was eight whole hours ahead of Moscow! It was not only her watch which told her that, but her tummy, too. She was not hungry for lunch in the least bit yet! Her tummy always told her when it was time to eat. The other passengers in the train had put forward their watches by one whole hour everyday. This was because the Russia Express had crossed eight different time zones to reach Vladivostock from Moscow. Therefore, it was one o'clock on their watches now. If youvhave ever seen for yourself how time at any moment differs in different countries, or even in places that are very faraway from each other, you will understand better than Irina why Moscow and Vladivostock have different times. Have you ever rung up a friend or a relative who lives on the other side of the 99

globe, around tea time, and been surprised to hear him sound most groggy? You probably jerked him out of his sleep! This happens because there is a difference of nearly 12 hours or so between his clock and yours. Time, the world over, can never be the same. Owing to the earth's rotation, the midday sun from which we measure our noontime can never be directly overhead at all places at the same time. When it is noon in New Delhi, it is certainly not noon in New York! In fact, it will be nearer midnight. Nearer home, Singapore has finished breakfast wjien you stretch yourself out of bed. Europe is still fast asleep. Geographers have carefully worked out how to measure the correct time in different parts of the world today. The earth has been divided into 24 time zones or belts covering 15 degrees longitude each. Longitudes are also called 'meridians', and are imaginary lines marked by man that run through the the north and south poles of the earth. There are 360 of these meridians altogether. It is logical that places lying on the same meridian will have the same solar time for they face the sun together. Places that are east or west of each other have different solar times. The difference in solar or local time is one hour for every 15 degrees of longitude. This makes a time zone. 100

You can make a simple calculation to see how this is so. If 360 degrees of longitude rotate completely in 24 hours, 15 degrees will take one hour to rotate. Therefore, the difference between one time zone and another, 15 degrees apart, is one hour. In those days when time zones did not exist, the world was a hotch-potch of local times. People set the clocks or watches according to the mid-day sun where one lived, so you can imagine how different their readings must have been, even in the same country! There were no meridians marked out alien. Most sailors used the time at their home ports as they roved the seas. They must^ have been surprised to find it pitch dark in certain places when it should have been , morning according to their time, or light in others when it was past their bedtime! S To get over this trouble, a meeting was held in Washington in 1884, where Britain and the U.S.A. urged international adoption of Greenwich in Britain as the 0 degree longitude or 'Prime Meridian'. A 24-hour count could begin from here for all the world to follow. Greenwich was chosen because it was the site of the Royal Observatory, set up in the reign of King Charles II, where the first proper time measurements were made. All other meridians are marked east or west of Greenwich up to 180 degrees each 101

—y

When the sun is directly over the prime meridian, it is noon in Greenwich Mean Time.

way. Since the earth rotates from west to east, the east is ahead in time—that is why we call Japan in the Far East, 'the land of the rising sun'. As we move east from Greenwich, we add one hour for every 15 degrees of longitude we travel. When we move west from Greenwich, we subtract one hour from Greenwich time for every 15 degrees. So if a place is three time zones or 45 degrees west of Greenwich, the time in that place is three hours behind Greenwich Mean Time or GMT, as the average solar time in Greenwich is called. Indian Standard Time is five and a half hours ahead of GMT. Astronomers at the Greenwich Observatory check their clock against the sun or a particular star. This is done by checking the exact time when the sun or the star crosses the meridian. The latter method of checking with the stars is called keeping 'sidereal' time, and it is useful for its accuracy. Correct time is also kept by all observatories in other countries, with special clocks. The Naval Observatory in Washington D.C. determines the correct time with a quartz crystal controlled clock, correct to 1/500th of a second per day. They broadcast time signals by radio. All countries keep a track of the time of other countries. When people travel from one country to another, they must change the time 102

on their watches according to time differences. Although time changes with each time zone, countries usually keep one local time based on a central meridian, even if they are spread over two time zones. Otherwise, imagine how awkward things would be if every town or city kept its own time! Mumbai and Kolkata are over 15 degrees apart, but like the rest of India, they follow Indian Standard Time which is based on the 82.5 degrees east longitude. In case of countries with many time zones, one local time is unsuitable. In the U.S.A., there are four different local times—Eastern, General, Mountain and Pacific Time! With due altering of time on your watch, you could catch trains and flights all over the world with ease, and keep appointments. Still, a strange problem remained. Take the case of a man who travels to London from New Delhi. He will have to put his watch fiveand-a-half hours behind. Now just suppose he keeps travelling west till he comes back to where he started. He would have put his watch behind by a whole day. If he started out on January 1, it would be December 31 if he travelled westwards. If he were to travel in the opposite direction, eastwards, he would keep putting his watch forward till he ended up putting it forward a full day when he came to the point he had started from. The date here would now be January 2. 103

It is indeed a strange situation. You lose or gain a day depending on which way you travel! A way was found to avoid a puzzling situation like this one. An imaginary line was drawn right down the earth's surface from North to South pole, in the middle of the Pacific Ocean. It was located at the 180 degree meridian and called the International Dateline. On both sides of this Dateline are two different dates. According to international agreement, whenever you cross this line the date changes. You gain a day if you are going west across the line, or lose a day if you are going east. The Dateline has some variations from the 180 degree meridian so that it does not divide land areas or islands. It would be most confusing to live in a place cut through by the Dateline—and so have two different dates on either side of it! Incidentally, the word meridian comes from the Latin word for mid-day, or meridies. So when the sun crosses your 104

meridian it is noon for you. East of this is morning or 'ante meridian', meaning before mid-day. We use the short form of 'a.m.' for this. For example, school begins at 8 a.m. or eight o'clock before mid-day. After midday 'p.m.' is the abbreviation for 'post meridian' when the sun has passed over the meridian. So we say dinner is at 8 p.m., or after mid-day. To express time from 12 noon to 12 midnight we use p.m., and for 12 midnight to 12 noon we use a.m. Your clock at home is numbered from 1 to 12, and you can always tell whether it is 9 o'clock in the morning or 9 o'clock at night, by looking out of your window. This can become confusing sometimes if somebody has a train to catch or a meeting to attend, and we forget to add a.m. or p.m. after the hours. For a long time, people have been using the 24-hour method to avoid much misunderstandings or mistakes especially in train and flight timetables, or for important timings. Here, the hours of the day are numbered from one to 24 instead of two periods of 12 hours each. After 12 noon, 1 o'clock in the afternoon becomes 1300 hours instead of 1 p.m., 2 o'clock becomes 1400 hours and so on. Minutes are shown after the hour and not to the hour. For instance, a quarter to three in the afternoon becomes 1445. A quarter past four will become 1615 hours. Here is a complete table for you to follow 105

when you make out your next party invitations. Remember the minutes follow the hours. 0100 hrs. 0200 hrs. 0300 hrs. 0400 hrs. 0500 hrs. 0600 hrs. 0700 hrs. 0800 hrs. 0900 hrs. 1000 hrs. 1100 hrs. 1200 hrs.

1 a.m. 2 a.m. 3 a.m. 4 a.m. 5 a.m. 6 a.m. 7 a.m. 8 a.m. 9 a.m. 10 a.m. 11 a.m. 12 a.m.

1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400

106

hrs. hrs. hrs. hrs. hrs. hrs. hrs. hrs. hrs. hrs. hrs. hrs.

1 p.m. 2 p.m. 3 p.m. 4 p.m. 5 p.m. 6 p.m. 7 p.m. 8 p.m. 9 p.m. 10 p.m. 11 p.m. 12 p.m.

Kaalachakra "The wheel of time (kaalachakra) rotates eternally through the four ages on earth..." These four ages or yugas were called satyuga, tretayuga, dvaparayuga and kaliyuga, the present age. The kali era is supposed to be the most decadent period in the system of four yugas, and is believed to have begun on the dawn of February 18,3102 B.C. Our own ancestors in India were deep thinkers and learned men. Even a long, long time ago, when the Western civilization was still very primitive, our philosophers had evolved their own scientific calculations and theories. Their profound wisdom and knowledge is reflected in the rich literature of our past—in ancient texts like the Vedas and the Pur anas. Here, one can read interesting accounts of the creation of the universe and the beginning 107

I am Time. Bhagavad

Gita

Chapter 10, 30

Summer

of time, and trace the histories of the gods. The precision with which our ancients, in their own way, measured time is astonishing. Time, they believed, stretches to infinity. Unlike later Western thought which viewed time as something that moves in a straight line from past to future, Indian philosophers saw time (kaal) as an endless cycle. This was the kaalchakra or 'Wheel of Time' which moves through the four ages or yugas which are repeated for an endless period. These ancient philosophers were thorough in whatever they did. Time division began with the smallest unit of time, and was calculated up to practically infinity. According to the Shiva Purana, which is well over 1,500 years old, the smallest unit of time in the natural day was the time taken to wink. This was one nimisha, fifteen of which made one kashtha. Thirty kashthas made one kala, while thirty kalas made one muhurta. Thirty muhurtas constituted one complete day. Calculations did not stop here but went much farther. Fifteen days made one paksha and two pakshas of the waning and waxing moon made one month. A month was counted from one full moon to the next. Six months made up one ay ana and two ay anas made a year. To chart the passage of time, the. ancient Indian calendar-makers divided the lunar year into 354 days, and the solar year was spread over twelve lunar months. We still use 108

the same seasons with their old names today, viz. vasanta or spring, grishma or summer, varsha or the rains, sharad or autumn, hemanta or winter, and shishir or the dews. Early poets and sages in India wrote lilting verses about the beauty of seasons. Chaitra was the first month of the year, falling in the spring-time, followed by Vaisakha, Jyaistha, Asadha, Sravana, Bhadra, Asvina, Kartika, Agrahayana, Pausa, Magha and Phalguna, the last month. The Saka calendar uses these same months. Eventually, ancient India adopted the sevenday week or saptaha from the West, and named the days after the corresponding planets. Sunday or Ravivara was named after the sun. Monday or Somvvara was named after the moon. Mangalvara or Tuesday was in honour of Mars. Wednesday which was named after Mercury was Budhvara, while Thursday was named Brihaspativara after Jupiter. Friday or Shukravara was dedicated to Venus, and Saturday or Shanivara was named after Saturn. Everything in ancient India had a religious or symbolic significance—for the gods ruled every part of life. The solar year was considered to equal one complete day of the gods. The period of the sun's ascent into the northern hemisphere was considered to be daytime for the gods, while its descent into the southern hemisphere constituted their night. Thirty solar years equalled a month for the gods. In 109

Autumn

Spring

Brahma

Vishnu

this way, 360 solar years made a divine year. Now you can imagine how old the gods must be! It was on the basis of these divine years that ancient Indian philosophers divided time into four ages or Yugas. The four yugas formed a mahayuga of 12,000 divine years, which equals 43,20,000 solar years. One thousand mahayugas made a kalpa. The Puranas tell us that thousands of such kalpas have come and gone, of which there is no record. Such figures are really too vast for us to be able to think about clearly! Indian lore states that one kalpa measures one day in the life of Brahma, the Creator. The subsequent night is equally long. Brahma's life span is considered to be 100 years long. By this reckoning, it stretches to practically infinity! Of these 100 years, only half are said to be over. Our ancestors further believed that our universe has been created in one day of Brahma's life, and will end in one night. Remember, this enormously long day spans 1,000 mahayugas or 43,20,000,000 years! The night of destruction is equally long. Furthermore, one Brahma is said to be followed by 1,000 such Brahmas. Then dawns the Age of Vishnu. One thousand Vishnus are followed by the Age of Shiva, and at the end of 1,000 Shivas alone will come the end of creation. Yet, this still does not mean the end of time— 110

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for only a fraction of the Creator's energy is claimed to be used! Time has no beginning and no end. It is eternal. In the face of such immense time scales, our months and even years seem tiny. By their intricate calculations, our ancestors did manage successfully to show what a tiny speck man is, compared to the enormous cosmic distances of space and time around. The ancient Indian calendar continued with some refinements. With the influence of Greek and Mesopotamian astronomy and astrology, these refinements were introduced for casting horoscopes and making predictions. Shadow clocks, sundials, water-clocks and sandglasses were some of the instruments used to keep time in ancient India. A typical waterclock was made of a small pot with a hole in the bottom which floated in a large tub of water. The time taken for the pot to fill was one ghati, or 24 minutes. Incidentally, the Hindi word for clock or watch, ghadi, is derived from ghati. Ghadi is also used as a word for time measurement. In the eighteenth century, an observatory was built at Jaipur which was equipped with expensive astronomical instruments in marble and precious metals. A number of sundials were also built here, including the 'Samrat Yantra'. This huge structure, built by Maharaja Sawai Jai Singh II, is the world's biggest sundial. It has a vertical height of 111

Mahesh

Jaipur observatory

36 m and a gigantic gnomon 27 m. This casts a shadow so big that one can follow its smallest movements very easily. This sundial is aligned exactly with a north-south meridian, and is accurate to within two seconds. Today, we have not lost touch completely with our past. Indian festivals are still celebrated according to the calendars devised long ago, and, as we earlier saw, the Indian Government uses both the Gregorian and the ancient Saka calendars.

113

No Beginning, No End Man has come on an amazing journey from the distant shadow clock to the atomic clock of today, accurate to a millionth of a second! He has indeed triumphed oyer the measurement of time. You must remember however, that all these comprise earth measurements. Time counts in the universe are vast and quite different. Suppose you had a Martian friend who was born on the same day as you, and you are twelve years old today. How old would he be? Twelve years old, of course, you would say; and according to the time reckoning on the earth, you would be quite right. But on Mars, conditions would differ. You saw how an earth year of 365 days is measured by our journey round the sun. A picture of the solar system will show that the nine planets revolve in varying distances 114

round the sun. Mercury is its closest neighbour, while Neptune and Pluto are an enormous distance away from the sun. So planets do not orbit it in the same time. The farther away they are, the longer is their journey. They spin at different speeds too, so the lengths of their days vary. Mars, in fact, takes 687 earth days to complete one revolution round the sun. It is farther away from the sun than earth, and moves slower in its path. Therefore, 687 earth days make up a Martian 'year'. You can figure out now that your Martian friend is about six Martian years old! It is obvious that our measurements of time cannot be used on other planets. You would need a different calendar altogether. If you had another alien friend, living on far-off Uranus, he would be an old, old man by earth years when he reached his first birthday. For Uranus takes 84 earth years to go round the sun once. And friends at the outer edge of the solar system, on Neptune and Pluto, would not have a birthday at all! (We are assuming a life span like ours on earth). Neptune takes 165 earth years to circle

vho was you are dhebe? say; and te earth, i Mars, days is ! sun. A that the [stances

the sun. Its day is less than 15 hours, so there are 90,000 days to Neptunian year! Pluto, with its vast orbit of 248 earth years, spins so fast that its day is barely seven hours long. So it has even more days to the year. It is unlikely, however, that life exists anywhere else in the solar system but on our planet. As we know more and more about outer space, questions keep cropping up regarding the age of the earth, of the universe and indeed, of time itself. For us even one year seems a long time! It is difficult to understand how very old the earth is. Till a century ago, this was a very big mystery. Scientists tried to unravel this mystery in some interesting ways. Some tried to estimate the amount of salty chemicals carried down to the oceans by rivers. Geologists tried to figure out the earth's age by land and ocean changes. Many conclusions were guesswork, but finally, not very long ago, scientists came close to solving this mystery. An exciting discovery enabled them to estimate that the earth has been around a good 4.6 billion years or so. They discovered too, that life on earth started about 570 million years ago. The first 345 million years marked the development of simple marine life. Giant reptiles like dinosaurs were the earth's inhabitants for the next 160 million years, and mammals appeared in the subsequent 65 million years. Man appeared on the earth 116

about one million years ago. However, we know only 5,000 years of his history. These vast figures have been worked out by studying a substance called uranium, which is found in some rocks. Uranium is a radioactive material—which means it is always letting off energy, rather like a bulb emits light. Uranium is converted to lead at a steady rate over millions of years. So the amount of lead in rock samples enables scientists to estimate the age of the earth. If you find all these time distances mindboggling, what about things older than even the earth, which existed before it did? To solve a good mystery one must go further back and further into time to look for clues. Can we reach the beginning of time itself? The exploration of the universe, conducted by astronomers, physicists and cosmologists is one of the greatest adventures of the twentieth century. Their findings in the last few years have revolutionized our knowledge and understanding of the universe. 'Cosmology' is the study of the universe at large, its beginning, its evolution and its ultimate fate. Cosmologists make use of information from giant telescopes, space probes and large computers that carry out their intricate calculations. Much of cosmology is mathematics, and cosmological ideas can be expressed in terms of equations, using paper and pencil and the mind alone. 118

Scientists have developed various kinds of optical and radio telescopes to study distant stars. Incidentally, the word 'telescope' is taken from the Greek word 'teleskopein' which is a combination of 'tele' meaning 'far' and 'skopein' meaning 'to see'. So a telescope is an instrument that helps us to see far off objects clearly. The Italian scientist Galileo made the first successful telescope to study heavenly bodies. The Milky Way was the name given to the band of white light which stretches across the sky. Galileo discovered that this band of light comes from a vast collection of faint stars which the naked eye cannot see. Our sun, its planets and the nearby stars also belong to this collection of a hundred thousand million stars, held together by the gravitational force. This cluster of heavenly bodies is called 'galaxy'— Greek word for 'milk'. The whole galaxy is spinning round its own centre. It takes between 220 and 230 million years to go round once! This period has been called the 'cosmic year'. Clearly, beyond our galaxy lie millions of other galaxies which appear to us as merely dim, misty patches. Who knows, there maybe more which we have not detected as yet! All these stars must have surely come from somewhere and at some time. Scientists believe they were made from dust and gases. When and where did these come from, in the first place? To grasp cosmic evolution, one must probe 119

Galileo invented a telescope with lenses, and studied the moon, planets and the sun.

at least several billion years back in time by studying objects billions of light years away Equipped with big telescopes today, astronomers can look back billions of light years into space. They are actually gazing far back into time! While looking at light from a faraway galaxy, they are actually seeing it as it was millions of years ago. There have been different theories about the origin of the universe. Modern astronomers believe that the universe came into existence at one particular moment with the 'Big Bang'— explosion in space. The debris and blazing gases from this violent explosion were thought to be flung, far out in space. The cooling of these scattered parts over several million years gave birth to galaxies whose matter has been expanding continuously. Our solar system was also believed to have been formed like this. The lava of the earth solidified after a vast period of time into our familiar world. Scientists found evidence that the entire universe is evolving and expanding. The rate at which galaxies seem to be simply flying apart tells them the date when all matter in the universe set out on its journey. "We were able to show that the matter in the universe must have been infinitely compressed about 15 thousand million years ago," says British astrophysicist, Stephen Hawking, author of the best-selling book, A Brief History of Time. 120

v

• And before that? "Time as we measure it simply did not exist," he comments. The other side of time is a dark mystery, greater than any mystery story you have read. Hawking is famous for his intensive research into certain dark areas in space, called 'black holes' or collapsars ('collapsed stars'). These are now seen as the remains or 'ghosts' of very large, 'dead' stars. Within a black hole, the gravitational attraction is so great that anything that goes in cannot come out. Not even light! How does this happen? At some stage in a large star's life, its nuclear fuel is exhausted. It becomes unstable and gravitationally begins to collapse inwardly on itself. The star shrinks after nuclear activity has ceased, to become a 'white dwarf'. In this process the star is reduced to one hundredth of its original size. Its gravitational pull becomes about 10,000 times more than the gravitational force of the original star. This dense star gives off little light. The fate of a white dwarf is decided by what is now known as the 'Chandrasekhar Limit', which is the maximum mass possible for its stability. This was named after the Indian astrophysicist Subrahamanyan Chandrasekhar who formulated it in 1930. He showed it was impossible for a white dwarf to be stable if its mass is greater than 1.44 times the mass of the sun. 121

Subrahamanyan Chandrasekhar (1910-1995)

The star contracts further, forcing the electrons and protons of its atoms to combine to form neutrons. The star now becomes a 'neutron star'. Its size is reduced to a fivehundredth part of the dwarf star and gravitational attraction becomes about 100,000,000,000 times the original star. As the light given off by the neutron star decreases, its energy and its size reduces further. At some stage even its neutrons are crushed out of existence and it becomes a 'black hole'. Within the black hole, matter may be compressed to a point of zero volume and infinite density. This is called a 'singularity' and it forms the core of a black hole. All laws of physics break down at a singularity.

Black hole

If this puzzles you, do not worry. It is only in the last few decades that scientists themselves have begun to understand the origin and nature of the universe! Even stranger to understand is the way a black hole behaves, drawing everything into itself like a bottomless pit. Falling into a black hole is one of the horrors of science fiction. Yet, scientists today have concluded that a black hole is fact rather than fiction. Its great gravity drags anything that passes close enough, and tears it to shreds. These fragments fall into the black hole and can never come out. For, to get away from its extremely intense gravity, the speed needed or the 'escape velocity' must be greater than the speed of light. Scientists are 122

quite sure now that nothing can travel faster than the speed of light. Therefore, if light cannot escape, nothing else can. No wonder it seems so black! This invisible black hole can be detected only by its gravitational force. It closes time and space within itself and cuts itself off from the rest of the universe. Light and even time are said to circle endlessly in a closed loop. A key ingredient to understanding the universe today, astrophysicists have found, is the union of space and time. In fact they call this 'space time'. In everyday life, space and time seem to be quite different things. You know that space extends in the three dimensions of length, breadth and height. We can see where things are located in space and travel through it more or less at will. But although we know what time is, it is almost impossible to describe. In a sense it does have a direction from past to present and future, but we can neither look into the past nor the future, and we certainly cannot move through time at will. As long ago as 1905, German physicist Einstein was suggesting that instead of thinking of space and time as two separate entities, they should be thought of as different parts of a single unified whole, 'space-time'. His special theory of relativity combines the two in the same set of equations and shows they can be stretched or squeezed. 123

Spaceship

Speed is a measure that relates space and time. Speeds are always in the form of miles per hour or kilometres per second and so on. You cannot have one without the other when you talk of speed. Earlier theories have now been measured and confirmed to great precision in very many experiments. There have been many fascinating conclusions. Einstein's special theory of relativity had suggested that if an object were to travel at or near the speed of light, it would appear to undergo some astonishing changes. If you could watch a spaceship travelling at the speed of light, you would see three effects. lime would pass more slowly on the spaceship in relation to time on the earth. The spaceship would appear to increase in mass. It would also appear to decrease in length. Later experiments confirmed that space and time are indeed warped at high speeds. Moving objects also increase in mass the faster they go. But the speed of light always remains constant. Objects that travel at the speed of light experience 'time dilation' or stretching of time, and shrinking of length. Time is thus intimately related to motion and space. Imagine what time dilation could actually mean! In the distant future, astronauts manning spaceships that travelled at the speed of light, might return home to find their 124

children older than themselves! For time would have passed more slowly for them than for people on earth. And if time dilation really proves possible, it could be used for all kinds of important things. Space laboratories travelling at the speed of light could be used for elaborate experiments. Exploration into deep space would become possible, for long space journeys at high speed could be easily finished in the lifetime of one space crew. However, light travels at the fantastic speed of a hundred and eighty-six thousand miles a second! Today's space probes move at a mere seventy miles a second or so, and it seems unlikely we could reach the terrific speed of light. But who knows, science fiction could indeed become fact one day! Very slowly, the implications of all these amazing discoveries began to dawn on cosmologists. The universe, they realized, might behave like the biggest black hole of them all, where everything was held together by gravity, and space-time formed a selfcontained loop! There was one big difference. Black holes pull matter inwards, towards the singularity. The universe on the other hand expands outwards fom the Big Bang. Indeed, it is like a black hole inside out. Einstein's equations, the general theory of relativity, had said that the universe could not be static but must expand or contract. Observations showed that the 125

universe is indeed expanding. The universe must have emerged from a point of infinite density, a singularity, about 15 billion years ago, his equations show. This is sometimes referred to as the 'cosmic egg'—a completely self-contained ball of matter, energy, space and time. It was indeed a superdense black hole before the Big Bang. This was perhaps the beginning of time! Having gone back to the beginning, cosmologists now looked ahead to the future. The universe is thought to reach a certain size after which expansion of the galaxies will stop and they will start contracting. The Universe will then collapse back into the final singularity, termed the 'Big Crunch'. This is taken to be the end of time. It has been calculated that the 'edges' of time and space may be removed to prove a universe with no boundaries at all. It is simpler to understand this rather complicated idea by representing the universe as a globe. Imagine the Big Bang as a spot on its surface drawn at the North Pole. As time passes, we imagine the lines of latitude drawn farther and farther away from the North Pole getting bigger all the way to the equator. This shows expansion of the universe. From the equator down to the South Pole, the lines of latitude decrease, corresponding to the universe shrinking back into nothing, as time passes. There is thus no discontinuity in time or 126

space. At the North Pole, there is no direction north for everything points south. This is because of the geometry of the curved surface of the earth. Similarly, at the Big Bang, there was no time past, but everything lay in the future. This is simply because of the geometry of the curved surface of space-time. The entire package of space and time, matter and energy, is self-contained. It is like walking a little away from the North Pole due north. In a little while you will be walking south. In the same way, let us go back to where we began. Suppose you clambered aboard a Time Machine and pressed the 'Reverse' button. Z...a...a...p... You would travel backwards in time, all the way to the Big Bang. A moment later, you would move towards the future even though you had not changed the controls of your machine! The gaps in our understanding of the laws and forces governing our physical world are still enormous. The challenge to solve the riddle of time has only just begun. It has taken us to the threshold of exciting mysteries of existence and the unknown future. One day, perhaps, we will redefine our concept of time. Till such time, the fascinating story of time cannot end. The limits are set only by the limits of the human imagination. No doubt, time alone will tell!

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A world without time! It would be a chaotic place to live in. Man has been trying ever to reckon time. He watched nature's clocks—the rising and setting of the sun, changing of the seasons, growth of a baby and mutation in all creation. From shadow sticks to sundials to waterclocks to the present day clocks that are accurate to one-millionth of a second and further—it is indeed the story of time. A most significant idea that has resulted through untiring research is the concept of time-space-continuum as an indivisible unity. Time remains a scientific mystery!

E 377 ISBN 81-7011-891-3