Archive for April, 2012

Tamil/Indian Solar calendar

April 12, 2012

This time the Tamil New Year day falls on 13th April 2012. After a gap of 4 years, this Indian Solar New Year day has again become the official Tamil New year day, after fall of DMK government which sought to obliterate the history of Tamil Era. At this point it will be good to be reminded about the history of Tamil calendar system, though officially we all use Gregorian calendar.


As an evolution process the Sun was our first time keeper. The time between two consecutive sunrises was rendered as one day. Initially mankind was satisfied to mark the times of the day as morning, noon, evening and night. Later he needed to be more specific and hence he divided the time between two sunrises into 24 parts and each interval was called one-hour. (This word Hour itself seems to have evolved from the Hindu word horai). Of course further divisions such as minutes and seconds also happened. Now we say One Earth-day is 24 Hours. Later on mankind wanted to keep track of number of days also. Here the Moon came to his rescue. He observed the phases of the moon to grow and decay in a periodic way. From no-moon (or new-moon) to full-moon and then back to no-moon, it took about 30 days (actually 29.5 days). This period was called as one-month, (or Lunar month). Then the need arose to keep count of the number of months also. By this time the man has become smarter and he observed a periodic north-south motion of the sun with respect to the equator of the earth, giving rise to different seasons, such as Spring, Summer, Autumn and Winter. This period of movement of the Sun was called as one-year. Here there was a problem. This earth-year period was observed to be about 365 days. This is more than 12 lunar months by about 11 days. With closer observations of celestial objects, the man was able to evolve a rational calendar for keeping time over long periods. He realised he needs to evolve a luni-solar system of calendar to keep track of time as well as plan his cultural and religious activities accordingly. Here-in somehow a uniform system could not be evolved. Some communities, even today go only by lunar-month and lunar year of 12 lunar months (i.e. 354 days).         

Astronomy behind Calendars:

When observed from the earth, Sun (and other celestial objects) appears to have two kinds of movement; (i) east to west around the earth creating day and night on the earth and (ii) north to south to north again across the equator of the earth accounting for an yearly period. In modern astronomy this apparent movement of the sun with respect to earth is known as ‘diurnal motion’. It was always known to Indian astronomers that earth is the one that revolves around itself and also around the sun, as referred in ancient Indian text ‘Aryabhatiya’. The apparent path of Sun around the Earth is known as ‘Ecleptic’ or ‘JyothishChakra’ in ancient astronomical texts. Ancient Indian astronomers first observed the ecliptic and marked them into sectors of 27 (stars) constellations and named them after their brightest stars. Lunar months were named after these stars. At the time of the 12 full moon days occurring in a lunar year, the moon will be close to 15 of these stars. Considering three pairs of stars- Poorva/Uttara Ashada, Poorattadi/Uttarattadi (i.e. Purva/Uttara Bhadrapada), Purva/Uttara Phalguni – 12 names for the lunar months were obtained as Chaitra, Vaisaka, Jyeshta, Ashada, Shravan, Bhadrapada, Ashvini, Karthika, Margasirsha, Pushya, Magha and Phalguni. During the lunar month of Chaitra, on full moon day the moon will be close to star Chaitra (or Spica). Same is the case with other months Vaisakha, Jyeshta, Ashada, etc. When solar year was considered, similar twelve months were marked on the apparent path of the Sun (relative to earth). The 360 degree path of ecliptic around the earth was divided into 12 equal parts of 30 degrees, called Rasis starting from Mesha rasi, followed by Vrishabha, Mithuna etc. These are the same as Zodiacal signs of western astronomy. The time taken by the Sun to travel across one rasi is defined to be a souramasa or solar month. The beginning of Mesha Rasi (Aries) known as Meshaadi (or Mesha Sankaranthi) is a fixed point on the ecliptic (apparent trajectory of the sun). This point is 180 degrees away from Chaitra. (i.e., on the full man day of lunar month Chaitra, the star Chaitra, the Moon, the Earth and the Sun will all be approximately on the same line across the ecliptic). This point was same as vernal equinox, around fifteen centuries ago. But, as confirmed by modern astronomy, these equinoxes drift continuously and oscillates around Meshadi to an extent of 24 degrees. This phenomenon is described as Precession and Trepidation of the equinoxes. This is due to rotation of  ‘earth’s axis of rotation’ around a vertical axis, (Like a top spinning on the ground in a slant position), the rotational period for 360 degrees being 25,800 years. The rate of this drift of equinoxes can be calculated easily from the above figures as 50.23” in angle per year.  In ancient Indian astronomy this is described by the name ‘ayanachalana’. The goal of the Western Gregorian calendar (used world over) is to keep the dates of the solstices and equinoxes fixed — (i.e. the sun is directly overhead at the Equator during both vernal and autumnal equinoxes on March 21 and September 23; and the sun is directly overhead at noon over the Tropic of Cancer, on the summer solstice June 21, and directly overhead over the Tropic of Capricorn on the winter solstice December 23; Kataka-Makara Sankaranthis or Dakashinayana and Uttarayana punya kalas). The Gregorian calendar, known as a Tropical calendar, is shorter compared to Sidereal calendar considered by Hindus, by this 50” in angle, corresponding to .0142 day. These are also called as Sayana and Nirayana systems. At the beginning of year 2008 vernal equinox on the ecliptic was situated nearly 23 Deg 58’ west of Meshaadi (i.e. approximately equivalent to 24 days). This is why the solar year presently begins with Mesha Rasi, on 13th April, 24 days after vernal equinox on 21st March. (In fact all sankaranthis have shifted away from equinoxes and solstices).

Solar Calendar as adopted by Tamils:

The solar year as adopted by Tamils is quite exact unlike Gregorian calendar which needs a leap year once in four years. Since the sections of the ecliptic are of equal size (i. e. 30°) and the sun’s apparent velocity is not constant, the time the sun needs to pass through each rasi ranges from 29.4 days to 31.6 days. Month-wise average number of days starting from Chaitra are 30.9, 31.4, 31.6, 31.5, 31.0, 30.5, 29.9, 29.5, 29.4, 29.5, 29.8, 30.3 days. The total number of days for the year works out to 365.3, which is very close to actual Sidereal year of 365.2564 days. The actual number of days in any month could vary as per the exact time when sun enters and leaves the particular rasi. For the present New Year, Nandana, the actual numbers of days in the months from Chitrai are: 31, 32, 31, 32, 31, 30, 30, 30, 29, 30, 29, 31 days – totalling to 366 days.

Stars and Rasis as names of Months:

Indian astronomers, for some reason, preferred to link the names of the solar months with those of the lunar months. Hence Mesha Rasi was linked with lunar month Chaitra and similarly other months. It was correct when vernal equinox approximately coincided with Meshaadi position, centuries ago. But as of now with Meshaadi lagging behind vernal equinox by 24 days, lunar month Vaisakha is more apt for Mesha Rasi. (But we still go on reciting, Chitrai-Mesham, Vaikasi-Rishabam, etc. In this respect Malayalees are better off. They call solar months by rasi names only). Several solar calendars associate Vaisaka with meshadi, the year beginning.

Wide Acceptance of Solar Calendar:

The above solar calendar was mostly accepted by all communities in India- Hindus, Buddhists, Jains and Sikhs. But some communities chose to adopt a luni-solar calendar with lunar months and a solar year, by introducing an adhik maas whenever required. Many other communities including Tamil Nadu chose to fully adopt solar calendar. Hence 13th April 2012 will be the new year day for Tamil Nadu along with Assam, Bengal, Kerala, Orissa, Manipur, Punjab etc. This also coincides with the traditional new year in Burma, Cambodia, Laos, Sri Lanka, Bangladesh, Nepal and Thailand.  Interestingly Sikh New Year day is known as Baisakhi. Names of the months vary slightly in different communities as names of stars or names of rasis or names of both with some names in the local languages. The 60-year cycle is also very ancient and is observed by most traditional calendars of India and China, and is related to 5 revolutions of Jupiter according to popular belief, or to 60-year orbit of Nakshatras (stars) as mentioned in Surya Siddhanta. 

Luni-Solar Calendar alignments:

In Luni-solar calendar, lunar months (12 x 29.5 = 354 days) keep shifting by about 11 days each year. Hence to re-align the lunar months with solar months, a thirteenth month (Adik Maas) is introduced in some years. There is a well defined method to decide when and where to introduce this extra month during a specific lunar year.  Vasishta Siddhanta, a treatise of Sage Vasishta, says that the Adhika Maas occurs after every 32 months, 16 days and 8 Nazhikais. A Nazhikai is 24 minutes. This new Hindu year 2012-2013 has an Adhik Maas and it is from August 18, 2012 to September 16, 2012. This extra month is known as Adhik Bhadrapad Maas. All festivals like Rama Navami, Janmashtami, Deepavali (Naraka Chaturtashi), Nava Ratri, Ganesh Chaturthi, etc  are based on Lunar calendar. Festivals like Chitra Pournami, Vaikasi Visakam, Karthigai deepam, Thai Poosam, Masi Magam, Panguni Utthiram etc are based on solar months. The Muslim calendar is the only purely lunar calendar in widespread use today. Its months have no permanent connection to the seasons. Muslim religious celebrations, such as Ramadan, may thus occur at any date of the Gregorian calendar. Earlier attempts to correct the situation, by introducing an adikmaas in Islamic year, were not accepted by Islamic religious heads.

Solar Calendar and Tamil literature:

It is observed that the above Solar calendar has been accepted by Tamils as early as 3rd Century AD or even earlier. There are several references in early Tamil literature to the Mesha/Chitrai new year. Nakkirar, the author of the Nedunalvaadai writes in the 3rd century that the Sun travels from Mesha/Chittrai through 11 successive Raasis or signs of the zodiac. Kūdalūr Kizhaar in the 3rd century refers to Mesha Raasi/Chittrai as the commencement of the year in the Pura-Naanooru. The Tolkaapiyam is the oldest surviving Tamil grammar that divides the year into six seasons where Chittrai marks the start of the Ilavenil season or summer. Silappadikaaram mentions the 12 Raasis or zodiac signs starting with Mesha/Chittrai. The Manimekalai alludes to the Hindu solar calendar as we know it today. Adiyaarkunalaar, an early medieval commentator or Urai-asiriyar, mentions the 12 months of the Tamil Hindu calendar with particular reference to Chittrai.


Unlike the Indian calendar(s) which measure the sidereal year (of 365.2564 days), the Western or Gregorian calendar directly measures the tropical year (of 365.2422 days). The difference is about 20 minutes per year, which is quite significant. This is due to the ayanachalana of 50”, in angle, per year mentioned earlier. Even this Gregorian calendar used world over today is not accurate. It errs by 26 seconds in a tropical year. The difference will add up to one day in 3323 years. It is any way much better than the earlier Julian calendar used all over from 45 BC up to 16th century AD, which erred by 11 minutes, 14 Seconds in a tropical year.England accepted the new revised Gregorian calendar only in 1751 AD, 150 years after it was proposed, and it had to advance their calendar by 14 days to correct the accumulated error. Since it was exactly two weeks, the days of the week did not get affected. After all this study and discussions two things that still elude answers are: (i) how did the Tamil Names for the months evolved – specifically – Ani for Jyeshta/Mithunam, Adi for Ashada/Katakam, Ayppasi for Ashwini/Tula, Thai for Pushya/Makara and Masi for Magham/Kumbam?; (ii) is there any historical evidence that Meshadi, the beginning of Hindu Solar year, was always moving (by one day every 72 years?) with respect to Gregorian calendar?.   

Happy Tamil-Solar New Year to all my readers.


1. Tantra Sangaraha of Nilakantha Somayaji, by K Ramasubramanian and M S Sriram, Hindustan Book Agency, 2011

2. Wikipedia