Time Reckoning

Modern and Vedic astronomy was born through man's first attempts to measure the passage of time by observing motions of Sun and the Moon. Thus, time reckoning is synonymous with astronomy even today. While modern method of time reckoning has changed over the years, Vedic methods remain unchanged as people continue to celebrate Ram Navami, Krishna Janmashtami etc as per Hindu calendar since Vedic days. This article presents different process of time reckoning and their significance in our daily life.


The moment we think of measurement of time, most of us recollect either grandfather's clock or our first Physics pendulum experiment using string and mass during school days. We also know how to adjust the period of this pendulum by increasing or decreasing its length. Yet another factor control this period is the earth's gravity while mass of the pendulum has no effect. This mechanical clock when synchronized with the mean solar time, it gives us the time on 24-hour basis. The mean solar time can be defined as a mean Sun which moves eastward along the celestial equator at average rate of true Sun. Greenwich Mean time(GMT) or Universal Time(UT) is simply a mean solar time measured from Greenwich, England and used in navigation and surveying for hundreds of years. Each country adopts its standard time based on standard meridian with respect to Greenwich. Though look simple, what if earth does not spin in its axis at uniform and constant rate? Well, there is a problem, Earth loses about 45 to 50 seconds in one century and in one millennium, the planet is 1.25 hours behind expected time schedule. Therefore, a better standard for the absolute measurement of time is the use of solar system dynamics. The orbital motions of the planets and of the moon are predictable to very high accuracy and are directly verifiable through observations. The resulting time is referred to as Ephemeris Time (ET).

In 1957, the International Astronomical Union Adopted Ephemeris Time as the standard and defined ephemeris second as 1/31,356,925.9747 of the tropical year 1900 at January 0 at 12 hours Universal Time. The difference between ephemeris time and universal time (DT) is obtained through observations of the Moon. The Moon's position is predicted with respect to ET but observed with respect to UT. Between 1900 and 1980, the slowing of the Earth's rotation on its axis had caused Universal Time to lag 50.54 seconds behind Ephemeris Time.

The Ephemeris time remained the basis of all time measurements until 1984. Then with the technological development, the complexity of celestial mechanics is now over with the advent of atomic clock. The atomic or SI second is defined as 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels (F=4 to F=3) of the ground state of the Cesium 133 atom. The SI second was carefully chosen to agree as closely as possible to be ephemeris second. Thus in 1984, SI second was adopted as the newest time standard and Terrestrial Dynamic Time (TDT) replaced Ephemeris Time. The accuracy of this atomic time is about 10-12. Currently, all electronic and computer clocks are calibrated with respect to this atomic clock and become independent of celestial system of time reckoning.

Today's calendar in its earliest form was based on the lunar cycle originated from the Romans. Each month had one lunar cycle and 12 such months in a year accounting for 354 days. To keep the year synchronized with the seasons, a leap month had to be added every other year. This is very much similar to the one adopted by Vedic calendar even today. This was later reformed by Julius Caesar in 46 BC and accordingly the year had 365 days and a leap day was added every fourth year. Thus, average length of a Julian year was 365 days and 6 hour but the tropical year (Sun returns to vernal equinox) is 11m 14s shorter. Consequently, after 128 year the Julian year start almost 1 day too late. In 1582, the difference was about 10 days and Pope Gregarious XIII reformed the calendar again and known as Gregorian calendar that we continue to follow even today. He made few exceptions for the leap year such as; the years divisible by 100 are not leap years except when it is divisible by 400. That is why year 2000 was a leap year.


The word "Jyotishya" in the Vedic literature connotes "Astronomy" which was recognized as the foremost of the six auxiliaries of Veda. The Vedic life (1000 B.C. to 400 B.C.) was noted for the performance of several rituals and sacrifices at prescribed times to satisfy heaven and God. Vedanga Jyotishya was the earliest of all Vedic text on astronomy and was an integrated part of the life of the Vedic people of whom Vedic priests were well versed. Accordingly, a civil day was divided in to 30 muhurthas, 1 muhurtha in to 2 nadikas i.e., 60 nadikas (Ghati) for a day. The text also mention 27 nakshatras* and tithis (longitudinal difference between Sun and Moon in steps of 12 degrees). The Moon covers 360 degree from new moon to new moon accounted for 30 tithis in a lunar month. A month was divided in two parts or pakshas, the bright half (Shukla paksha) and the dark half (Krishna paksha). A tithi that is current upon Sunrise is tithi of the day. Thus a day is reckoned from Sunrise to Sunrise and time is reckoned in nadies or ghaties and in their fractions (1ghati = 24 minutes) from Sunrise. Names of the lunar months** were given based on the nakshatra in which the full moon occurred. For example, during Chaitra month, Moon will be in or closer to Chitta nakshatra during full moon. Similarly, 12 solar months were also identified and when two new moons occur in a given solar month, the lunar month is reckoned as additional month thus correcting the difference between solar year and lunar year.

The first point of the nakshatra Ashwini (near the star zeta) is the first point from which the longitude is measured. All the planets are supposed to have zero longitude (first point Ashwini) at the beginning of the maha-yuga. The beginning of current Kaliyuga is an epoch, which is presumed to have commenced on the midnight between February 17 and 18, 3102 B.C. The number of civil days elapsed from a given epoch is known as ahargana. This is the basis for computation of all planetary positions in traditional almanac. A solar year is reckoned from Saka era (78 AD) in the south and Vikrama era (57 B.C.) in the north whenever Sun transit over Ashwini. Similarly, a lunar year (samvatsara) is reckoned whenever a new moon occurs in or close to Ashwini after the end of month Phalguni. This is how and when we celebrate Sauraman and Chandraman yugadi respectively as a Hindu new-year day. A cycle of 60 lunar years has been given names (Prabhava, Vibhava .etc) and this cycle repeats. For example, the lunar year Tarana in 2004-2005 will repeat again after 60 years in 2064. Thus according to Vedic literature a full human life is considered to be 120 years comprises of two such cycle. This is the total number of years accounted under Vimshottary dasha system.

Vendanga-jyotishya is in the form of various sutra, a style noted for its depth of contents continue to be in use for a long time until the invasion of India by Alexander the Great in fourth century B.C. After Greco-Roman contacts with India, a new class of astronomical literatures called siddhantas started emerging. An important development in this literature was the gradual replacement of nakshatra system by 12 signs of the zodiac, Mesha, Vrishabha, Mithuna..Meena, similar to the animistic notations of the Babylonians and Greeks. Accordingly, 27 nakshatras consisting of 108 parts (27x4) divided by 12 gives 9 parts for each sign. Thus, Mesha made up of Ashwini, Bharani and 1 part of Kritika (4+4+1=9) and so on. In addition, name of the solar months was identified with the respective sign. A few centuries after Christian era Indian astronomers developed new mathematical tools and methods for promoting astronomical calculations. Spherical trigonometry is one such area developed side by side with algebra and geometry added veneer of accuracy to the study of several astronomical phenomena. Thus newly emerging siddhantas were set of rules (including thumb rules) arriving at solutions to the complex astronomical problems. Among the 18 siddhantas Varahamihira, the great grand master of astronomy as well as astrology, ably codified Saura (Surya), Paitamaha, Vasistha, Romaka and Paulisa during 505 A.D. He reiterated that Surya siddhanta was the most accurate of all and became the basis of many traditional almanacs published even today from various parts of India. Surya siddhanta in the current form has no human authorship associated with it but, represents contribution from several noted astronomers over the years.


We all well versed with modern time keeping to the extent that most of us maintain hourly/daily/weekly/monthly log or schedule of activities with the help of computers since it has direct economic significance in our daily life. In the absence of modern time keeping systems, the almanacs (Vedic) were the only reliable and consistent timekeepers of all past events that enable people to celebrate and enjoy all traditional feast and festivals even to this date. Most important of all, living in harmony with the nature was the key to the successful, peaceful and happy life during Vedic days. Every species in this earth follows certain hidden rule of the nature in creation, development and destruction with respect to time. Biological make up all species should be in harmony with the nature during its entire development process. However, when ever this process goes out of balance or become arrhythmic the misery strikes. By nature, humans tend to go arrhythmic more often than other species, with the result encounter more challenges in every walk of life. Vedic people had solutions to such problems and came up with muhurthas (Auspicious time) for all major activities that can be found in any almanac for guidance, a tradition continuing even to this day. A logical extension of this gave rise to the evolution of Astrology (300 B.C to 500 AD) that formulated effect of different celestial objects and their movements upon an individual right from cradle to grave.

In India, Ayurveda and Jyothishya (Astrology) go hand in hand while treating patient in the past. The physician checks pulses at different places and then try to ascertain patient's rhythmic cycle through astrology to come up with right treatment. The scientific reasoning for this is human species undergoes three different cycles from time of birth known as biorhythm. They run simultaneously in a cyclic manner with periodicity given as follows.
1. Physical - 23 to 24 days (probably connected to cell's regeneration cycle)
2. Emotional - 27.3 days (Moon's celestial cycle that cover 27 star in 27 days)
3. Intellectual - 33 days.

If we multiply all these numbers and divide the product by 360 the result is around 60 years (Samvatsaras - Lunar year). From there every thing start all over again. That is why if we know the birth star that helps us to keep track of our rhythmic (Emotional) cycle.

All human behavior, conditions and actions are manifestation of this rhythmic cycle. That is why even sharp shooter or golfer can miss his simplest putt. Some time we are more energetic and some time very timid. While the above system is very simple, Vedic systems are still more complex that involves position of different planets from the day of birth. People have got all kinds of miss-conception and thinking that what planets got to do in our life? Well, it is one of the best ways to keep track of our biological rhythm ever since we were born and each birth and its biorhythm is unique by this representation and helps monitor changes in our physical, mental and intellectual faculties.
In Vedic astrology, vimsottari dasha system is a process by which this is accomplished that helps in future prediction.

* 27 Nakshatras:

1.Ashwini; 2.Bharani; 3.Kritika; 4.Rohini; 5.Mrigasira; 6.Ardra; 7.Punervasu; 8.Pushya; 9.Ashlesha; 10.Magha; 11.Hubba; 12.Uttara; 13.Hasta; 14.Chitta; 15.Swathi;16.Vishakha; 17.Anuradha; 18.Jeshta; 19.Moola; 20.Poorva Ashada; 21.Uttara Ashada; 22.Shravana; 23.Dhanishta; 24.Shatabhisha; 25.Poorva Bhadra; 26.Uttara Bhadra; 27.Revathi.

**Lunar months:

1. Chaitra (Mar-Apr); 2. Vaishakha (Apr-May); 3. Jyeshta (May-Jun); 4.Ashada (Jun-July); 5.Shravana (Jul-Aug); 6.Bhadrapada (Aug-Sep); 7.Ashwija (Sep-Oct); 8.Kartika (Oct-Nov); 9.Margasira(Nov-Dec); 10.Pushya (Dec-Jan); 11.Magh (Jan-Feb); 12.Phalguni (Feb-Mar).

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