quest for the right date

8/14/2019 Quest for the Right Date

1/7

Quest for the right dateBy

Shivaprasad M Khened, Curator Nehru Science Centre, Mumbai

Introduction

At the dawn of the New Year, which we all look up to with a hope that it will bringin peace prosperity and fulfill all our desires, it is time to spare a thought for thecalendar. The calendar is a system designed to reckon time in periodsconvenient to the conduct of civil life. We experience three natural cycles of time:the day, the month and the year. It is natural to assume that these are related butthe illusion of stability that attends them belies the comedy of errors and falsehope that is their history. Most of the energy spent in calendric pursuits has gonein the essentially fruitless task of reconciling the cycles of the sun (agriculture)and the moon (religion) using the doubly irreconcilable unit of the day.

Calendars and human society

Calendars are generally based on the natural cycles of moon phases andseasons. Moon has always influenced the timing of different religious festivals,and seasons, and the Sun has influenced the time of sowing and harvesting.Calendars based on Moon observations and study (called the lunar calendars),and those based on the observations of the Sun (Solar calendar) were usedwidely in different cultures of the world. Even the economic activities dependedheavily on the calendars and continue to do so even in the modern days.Therefore it would not be overstatement to state that calendars are inextricablylinked with the human society. Throughout history, different civilizations havedevised numerous ways of keeping track of time, and documenting the days asthey pass, culminating into various calendar systems.History of Calendars

The history of the calendar begins with the fascinating history of the humanendeavour to organize their lives in accordance with the sun and stars. Thecelestial bodies play an important role in the formulation of the calendars. Mostcalendars are founded upon some combination of celestial events. The Earthsrotation determines the day, the lunar cycle a month, and a revolution of sun by

our planet, a year. The current system of usage of calendars internationallyfollowed for all trade, commerce & other international dealings is the Juliancalendar with Gregorian Correction or simply called the Gregorian calendar.


2/7

Calendars of antiquity

Uses of various calendars have been known for a very long time. One of the

oldest & classic calendar systems is our very own Hindu calendar systemestimated to have been used from around 1000 B.C. Its based on the lunarrevolutions and has adjustments (intercalation/extracalation) to solar reckoning.History has also shown that calendars have been around for many years invarious other civilizations and cultures.Of the variety of other calendars in useeven today, probably the most well known, are the Chinese, Hebrew, Islamic,and Gregorian time keeping systems. While each of these systems is unique inhow it is used, they all share a set of common features, even borrowing fromeach other in ways that are not easily recognized. Like all great efforts thatrequire the dedicated collective work of a group of people, the establishment of atime-keeping system is no trivial matter. It required knowing how to make

observations, knowing which observations to make, and knowing how to keeprecords over a long period of time.

Hindu calendar

The earliest of the Hindu calendar is known from the texts of 1000 BC. It dividesan approximate solar year of 360 days into 12 lunar months of 27 days accordingto the Taitriya Samhitas and also according to the Atharva Vedas. The resultingdiscrepancy was resolved by the intercalation of a leap month every 60 months.The year was divided into three thirds of four months, each of which would beintroduced by a special religious rite, the chaturmasya. Each of this was further

divided into seasons or Rtu: spring (Vasanta), from mid March until mid May;summer (grisma), from mid May until mid July; the rains (varsa), from mid Julyuntil mid September, autumn (sarad) from mid September until mid Novemberand winter (hemanta) from mid November until mid January and the Dews(sisira), from mid January until mid March. The months were counted from fullmoon to full moon and were divided into two halves Shukla paksa of waxingperiod and krsna paksa of waning period. The new moon days were observed asamavasya and full moon as purnimas. The month had theoretically thirty days(tithi) and the day (divasa) thirty hours (muhurta). A new form of astrology that isin vogue today is based on the old Hindu calendrical system, which did under goa change in its classic from according to the Surya siddhanta in 4 th century AD.

The calendar has not always been the way it now is. It has been changed manytimes, and may change again because problems in calendar making areastronomical. This concept has even been evidenced in ancient Indianmythology. In India the reference of the calendars and their controversialinterpretation can be traced back to the period of great epic Mahabharata. Wehave all heard or read about the Vanavasa (period of exile) and agnyatavasa (theperiod of incognito living) that the Pandavas were supposed to take in obeisance

2


3/7

of Yudhisthars promise. The battle of Kurukshetra was fought with aconsideration that the Pandavas according to Duryodhana failed to keep theirpromise. Duryodhana claims that the Pandavas had failed to keep theiragreement to stay in exile for twelve years and in hiding for one. HoweverBhisma reckoned that they have kept the agreement, and Bhisma substantiated

his argument with the fact that the calendar adds an extra month every fiveyears. The interpretation of the calendar or the complications involved in thecalendar making was perhaps one of the reasons for the great battle ofMahabharata. This episode elucidates the complications associated with thecalendars and their rightful interpretation.

Measurements of Day, Month and Year

For the early calendar makers sunrise and sun set provided the day, while fullmoon, the month. Today, the celestial bodies provide the basic standards fordetermining the precise measurement of the day, month and the year. The day

can be measured either by the stars or by the sun. If stars are used, then theinterval is called the Sideral day and is defined by the period between twopassages of a star across the meridian. The mean Solar day is 24 hours, 3minutes and 56.55 seconds long.

The month is determined by the moons passage around the earth. There are twokinds of measurements for the month, first the period taken by the moon tocomplete an orbit of the earth and second, the time taken by the moon tocomplete a cycle of phases. The first is defined as the orbital month the problemwith this is that the moon's orbit is elliptical and it will be travelling faster whencloser to earth (nearest = perigee) and slower when further away (furthest =

apogee) and therefore has anomalies. The Anomalistic month is the timebetween perigees (27.55455 days mean value). The second measurement of themonth is called the synodic month (synod = meeting, in astronomy it meansconjunction or lining-up)with an interval of 29.53059 days; the synodic monthforms the basis of the calendar month.

Calendar makers problem also results from the length of a year. The Earth doesnot rotate whole number of times for each revolution of sun. The Sidereal year isthe time for the Earth to return to the same position relative to the fixed stars(365.25636 days mean value increasing by 0.00000012 days per century).Because it is slightly longer than the tropical the equinoxes will gradually creepwestward around the ecliptic by 1 in 71.71 years or 360 in 25800 years. Thecommon year is called the Tropical year meaning the time between springequinoxes (365.24219 days mean value decreasing by 0.00000614 days percentury). Because the Earth's orbit is elliptical it will travel faster at perihelion(closest, now early January) and slower at aphelion (furthest, now early July).This means that the season around perihelion will be shorter than the one aroundaphelion. Currently the gaps between equinoxes and solstices are, starting at theNorthern Hemisphere Spring Equinox, 92.72, 93.66, 89.84, and 88.98 days. The

3


4/7

southern hemisphere gets a few extra days of winter and the northernhemisphere gets a few extra days of summer. Choosing either of the yearsleaves the calendar maker in an awkward position of having the following NewYear beginning in the middle of the day.

Julian Calendar

A prominent predecessor of the Gregorian calendar is the Julian calendar. Of theseveral calendars of antiquity, the Egyptian and the Roman calendars developedinto the Julian calendar, which was used for more than 1500 years. The Romanrepublican calendar, introduced around 600 BC, was a lunar one, short by 10.25days of a Tropical year. It included an extra intercalary month, every two years,which fell in late February. Nonetheless, by around 50 BC, the lunar year hadfallen eight weeks behind the solar one, and it was clear that the Romans wereout of Sync.

There was total confusion when Julius Caesar came to power as the Romans355 day lunar calendar was 80 days out of sync with seasons when Caesar tookthe throne. Julius Caesar it is believed got acquainted with the Egyptian calendaron the same trip during which he got to know Cleopatra. He then came in contactwith the famous Greek Egyptian astronomer, Sosigenes. In the year 46 BC,Sosigenes convinced Julius Caesar to reform the calendar to a moremanageable form. Sosigenes' message to Caesar was that the moon was a nicegod but knew nothing about when things happen. Armed with this informationCaesar returned to Rome and made big changes. The old lunar system withintercalary months was abandoned and a new solar system was introduced withfixed month lengths making 365 days and an intercalary day every forth year in

February which would have 29 or 30 days. To shift the equinox back to March 25he added three extra months to 46 BC making it 445 days long ( 'the year ofconfusion') and the Julian calendar began on 1st January 45 BC. In recognitionof his contribution to the calendar reforms the month of July is named in hishonour.

Caesars nephew Augustus (originally named Octavius) also did some cleaningup of the calendar details of which are not clear. One source (Britannica)suggests that the priests got the leap years wrong having one every third year forforty years so he had to skip a few until 8 BC. In recognition of this, they renamedSextilis with August in his honour but had to pinch a day from February to make itthe month of August have the same length of days as July. The tradition haslasted until today and therefore contrary to any logic the immediate months ofJuly and August have 31 days each.

Anno Domini

Things went smoothly for a while; the seasons were finally put in proper place inthe year and festivals were happening at sensible times - almost. At the Council

4


5/7

of Nicea in 325 AD, Easter was decreed to be the first Sunday after the full moonafter the vernal equinox. The early Christians were keen to cleanse contraryideas (like the spherical Earth) so in 526 AD; the Abbot of Rome, DionysiusExiguus proclaimed that the birth of Christ should be the event from which yearsare counted. He also calculated the event to be from December 25 and asserted

that it should be called 1 AD (Anno Domini = in the year of our Lord) and the yearpreceding it should be called 1 BC (now meaning Before Christ) with prior yearscounted backwards. The omission of a year zero was a dumb idea.

About this time the seven day week was introduced. Although it may haveappeared earlier in the Jewish calendar and also in the Hindu calendar it wastidied up in the fourth century. Cycles of from four to ten days had previouslybeen used for organising work and play. Seven was chosen apparently inacknowledgment of the Genesis story where God rested on the seventh dayalthough there is a strong suggestion that it also reflected the seven gods visiblein the sky as the planets, sun and moon.

Pope Gregory XIII

By the middle ages the seasons had slipped again. Pope Leo X tackled theproblem in 1514 AD by engaging a number of astronomers, including the famousCopernicus who quickly recognised that there was a more fundamental problemthan rearranging the calendar and suggested the rearrangement of the universeby putting the sun at the center as against the earth. The Church though did notaccept the suggestions. Half a century later Pope Gregory XIII was sane enoughto have another go to sort out the discrepancy and assembled a team of expertsled by the German mathematician Christoph Clavius(1537-1612) and Italian

physician and Astronomer Aloisius Lilius who spent ten years finding a solution tothe problem. By 1582 AD the Julian calendar was full 13 days behind theseasons. By then the Christian churches had scheduled certain of its feasts, suchas Christmas and the saints days, on fixed dates. The Julian calendar, whichwas running 13 days behind the sun, had little or no effect on the lives of theordinary folks, but it disturbed the functioning of the Church, because it pushedthe holy days into wrong seasons. This prompted the church to issue clearanceto Pope Gregory XIII to implement necessary changes in the calendar.

Gregorian Calendar

The change made by Gregory XIII to the calendar was this: skip ten dayssometime to bring the seasons back in line and skip a few leap years now andagain. The extra day every fourth year is too much so skip the leap year at theend of the century. This is now a touch short so put back a leap year every fourthcentury. The rule is: a year is leap if it is a multiple of 4, it is not leap if it is amultiple of 100, it is back to being leap if it is a multiple of 400. Since this stillproduces an error of a day in 3,323 years we will also skip the leap year in 4000AD. So in 1582, Pope Gregory XIII, decreed that the day after October 4, 1582,

5


6/7

would be October 15, 1582.And according to the prescribed rule 1600 was aleap year but 1700, 1800 and 1900 were not and the year 2000 AD was again aleap year.

The changeover to the Gregorian calendar was not smooth. France, Spain, Italy,

and Portugal changed in 1582; Prussia, Switzerland, Holland, Flanders and theGerman Catholic states in 1583; Poland in 1586 and Hungary in 1587. TheProtestant countries weren't too keen to follow, so for nearly two centuries therewere two calendars running in Europe ten days apart.Matters came to a head in1700 when the Protestants had a leap year and the Catholics didn't, increasingthe gap to 11 days. Denmark and the German Protestant states changed in 1700and Sweden came up with the brilliant plan of simply skipping all leap years untilthey caught up in 1740. England and America switched over in 1752, skipping 11days by making September 3 as September 14 and shifting the start of the yearto January 1. There was much unrest - 'give us back our eleven days' was apopular campaign slogan. Many other countries were slow to adopt the standard

and it was not until the early twentieth century that the entire world was finallysynchronised. Japan changed in 1872, China in 1912, Bulgaria in 1915, Turkeyin 1917, Yugoslavia and Rumania in 1919 and Greece in 1923. The Gregoriancalendar is now recognised world wide although there are still many othercalendars running alongside it for religious purposes.

The Millennium confusion

When did the 21st century begin? Because we have no zero year the firstcentury comprised years 1 to 100, the second, years 101 to 200, the third years201 to 300 and so on. Clearly 2000 AD is the last year of the 20 th century and

2001 is the first year of the 21

st

century. The new millennium technically hasbegun on 1st January 2001. This technicality however did not deter people fromfeeling that 1st January 2000 was the millennium changeover just as they did inthe Middle Ages for 1000 AD.

Calendars in India

In India calendar reform took place in 1957. The National Calendar of India is aformalized lunisolar calendar in which leap years coincide with those of theGregorian calendar (Calendar Reform Committee, 1957). However, the initialepoch is the Saka Era, a traditional epoch of Indian chronology. Months are

named after the traditional Indian months and are offset from the beginning ofGregorian months.

In addition to establishing a civil calendar, the Calendar Reform Committee setguidelines for religious calendars, which require calculations of the motions of theSun and Moon. Tabulations of the religious holidays are prepared by the IndianMeteorological Department and published annually in The Indian AstronomicalEphemeris.

6


7/7

Despite the attempt to establish a unified calendar for all of India, many localvariations exist. The Gregorian calendar continues in use for administrativepurposes, and holidays are still determined according to regional, religious, andethnic traditions. Years are counted from the Saka Era; 1 Saka is considered tobegin with the vernal equinox of 79 AD. The reformed Indian calendar began with

Saka Era 1879 AD, Caitra 1, which corresponds to 22nd

March, 1957. Normalyears have 365 days; leap years have 366. In a leap year, an intercalary day isadded to the end of Caitra.

Conclusion:

Calendars have held sacred status for they help in maintaining social order,provide the basis for planning of agricultural, economic and industrial activities.Calendars also provide basis for maintaining cycles of religious and civil events.

Irrespective of what their scientific sophistication is, calendars must ultimately bejudged as social contracts, not as scientific treatises. Because calendars arecreated to serve societal needs, the question of a calendar's accuracy is usuallymisleading or misguided. A calendar that is based on a fixed set of rules isaccurate if the rules are consistently applied. For calendars that attempt toreplicate astronomical cycles, one can ask how accurately the cycles arereplicated. However, astronomical cycles are not absolutely constant, and theyare not known exactly. In the long term, only a purely observational calendarmaintains synchrony with astronomical phenomena. However, an observationalcalendar exhibits short-term uncertainty, because the natural phenomena arecomplex and the observations are subject to error.

********************************************************************************************

7

quest for the right date

Documents