Tamil Calendar

This article describes the basis on which Panchangam calculations are made and the logic behind the determination of the almanac dates of birth, anniversaries as well as religious events.

Tamil calendar - Diagram

(click on the diagram to enlarge it)

The Tamil calendar

Calendar is one that describes a day and time on earth as perfectly as possible.

Assuming the Earth to be at the centre of the universe, all celestial objects, the sun, moon and the stars appear to be on a big sphere around the Earth. This is an apparent sphere of course. But due to the distances of celestial bodies it can be assumed. In astronomy this is called the celestial sphere. Relative to the earth’s rotation around its axis the celestial sphere would be making one complete rotation around the earth, in the opposite direction, in 24 hours. The axis of rotation will be the same as that of the Earth. Corresponding to the earth’ poles we will also get celestial north and south poles at the points where the axis meets the celestial sphere.

On this celestial sphere the stars are fixed in their positions. Though in actuality stars do move constantly, their distances from us are immeasurably great that relatively their motions are very diminutive and in the celestial sphere they are permanent in their position. Since their positions are fixed many shapes can be imagined by joining the stars. These are called constellations.

The whole celestial sphere is divided into 12 equal stripes. Each stripe will have a range of 300 on sky. These stripes are named after the main constellations found in them. These are called the zodiacs. Hence we will get 12 zodiacs viz. Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces.

While the stars are ‘fixed’ in their positions on the celestial sphere the planets move among them; that is through the zodiacs. This is due to earth’s rotation around the Sun and each planet’s rotation around the sun.

The sun moves through the whole 12 zodiacs within a year, since the earth makes one complete rotation around it in that period. The period of time for the son’s movement between subsequent entries into the zodiac of Aries is determined as a year in the Tamil calendar.
Of the planets Jupiter and Saturn, the two biggest and most influential on earth due to their gravity, come together in the same Zodiac once in sixty years.

Hence in the Tamil calendar 60 years are identified and named. They occur in cyclic order.

Each Tamil month is determined by the period the sun ‘dwells’ in each zodiac.

Sun’s position

Name of Tamil month

Aries Chiththirai சித்திரை –April
Taurus Vaikaasi —- வைகாசி May
Gemini Aani   ——- ஆனி June
Cancer Aadi ——– ஆடி July-
Leo AavaNi —– ஆவணி August
Virgo Puraddaasi- புரட்டாசி September
Libra Aippasi —– ஐப்பசி October
Scorpio Kaarththikai- கார்த்திகை November
Sagittarius Maarkazi – மார்கழி December
Capricorn Thai ——– தை January
Aquarius Maasi ——மாசி February
Pisces Panguni —பங்குனி March

The moon goes through the whole 12 zodiacs in just one month. It waxes to the maximum, ie full moon when it is in the opposite zodiac to that of the sun and wanes to the minimum, ie new moon when it is in the same zodiac as the sun. To describe the moon’s position better, the whole sky is divided into 27 ‘Nadchathiras’. Each ‘Nadchathira’ is actually a space around a prominent star. Each Nadchathira is again divided into 4 smaller parts which are called the Nadchathira Pathams. Each zodiac will have 2 1/4 Nadchathiras in it. The moon will roughly be in 1 Nadchathira each day.
Each day is described (in addition to the month and year) by the Nadchethira, the moon phase and named in a cycle of seven after the ‘planets’ Sun, Moon, Mars, Mercury, Jupiter, Venus and Saturn.

The earth is assumed to be stationary. The celestial sphere makes a complete rotation from east to west in a day or 24 hours. On the celestial sphere the sun moon and all the planets journey from west to east.

The daytime is fixed as between sun rise and sun set. Since the sun moves from west to east on the celestial sphere, the celestial sphere with all the stars in it will rise earlier than the sun each day. As the sun makes one complete rotation on the celestial sphere, each star on the sky will rise with the sun once in a year. That means the stars will rise earlier than the sun by 24 hours in a year. So in one day the stars rise (24*60)/365 minutes, roughly 4 minutes early.

The moon on the other hand will rise late each day as its eastward motion on the celestial sphere is more than 12 times as fast as the1 the sun. On the new moon day the sun and the moon rise together. So the moon will rise later than the sun by 24 hours between subsequent new moons. That occurs roughly in 28 days. So each day the moon will rise (24*60)/28 , roughly 52 minutes late.

The movements of the planets on the celestial sphere are irregular. They show retrograde movement. Those planets which are nearer to the sun than the earth reverse their journey half way in addition to making many retrograde movements in between. The two planets, Venus and Mercury in this position are always either morning or evening ‘stars’. In the celestial sphere they are always within 3 zodiacs from the sun. Those which are further from the sun than the earth make a retrograde movement after entering a zodiac initially. This is because the movement of the earth around the sun is faster than these planets and projected from the earth against the backdrop of the zodiacs at infinite distance their positions go back into the former zodiacs soon after entering a new one. This will not happen if the planet is in the centre portion of a zodiac.

For the fixing of time two more additional things, to that of a day are mentioned. One is the zodiac which was at the eastern horizon at that time and the other is the position of planets in the zodiacs. Thus mentioned the time will only be approximation for two reasons. First, each zodiac has a width of 300 on the sky and has duration of two hours for its complete rise over the horizon. Second each planet can exist in a zodiac for a long time (relative to minutes and seconds), sometimes for years. To rectify the first, by how many degrees (the angle between the western border of the zodiac and eastern horizon) the zodiac has risen above the eastern horizon is calculated. As regards the second, the position of the planets in the zodiacs should be further particularised to the Nadchathira pathams and précised to the degree or angle from the western border of the Nadchathira patham.

While the fixing of a month by the Tamil calendar coincides with the sun’s position in a zodiac, the fixing of an annual day as well as religious events require an additional celestial occurrence, the moon’s position. When the moon is in the same Nadchathira on subsequent same Tamil month, then it is considered the annual day viz for birthdays, anniversaries etc.

Done in this manner the Tamil calendar is more scientific, accurate and referring to the earth’s position in the universe rather than to any event that happened on the earth.

Tamil New Year

The science of the
Tamil new year

One year is the time taken by the earth to go around the sun. When defining it that way we have to consider the centre of the earth.

Speed of the earth around the sun is about 30km/sec. So if you are going to take a point/country on the surface(and not the centre) of the earth there will be 24 hrs difference between the times of New year celebrations on the adjacent points west and east of the international DATELINE. In 24 hours earth would have moved 24 X 60 X 60 X 30 km (2592000 km), which means one full round about the sun by the earth becomes meaningless if you consider any point on the surface.

Moreover 365 days is an approximation and assumes that the circumference of earth’s orbit is exact whole number times of its own circumference.

The ancient man could have arbitrarily taken one year as between subsequent spring/summer/winter times or as between any events that are annual in occurrence. It would have really been a convenient method for him to determine ages of living things. But for the present day scientific man, precise determination is needed.

There is a mathematical method of determining an year. Go to your roof top in the night, with a hollow cylindrical tube. Observe a star through the tube. Fix the tube in that position and note the time. Say the time is 9 pm. The next day the same star will be seen through the tube at roughly about 8.56 pm. The following day at 8.52 and so on. When the star could be seen through the tube again at 9 pm, it would be exactly one year from the time we started. This is based on the assumption that the stars are at infinite distance from the earth, so it makes little difference from wherever you make this calculation.

Our ancestors did just that. But instead of hollow tube mentioned above, they noted the entry of the sun into a zodiac sign; the constellation of Aries.

Now let’s see how the concept of constellation came to be. The earth rotating about its axis is the real happening. The sun, moon, stars and all going round the earth in 24 hours is the relative happening, which we see. The earth moving (rotating) from west to east is the real happening, all celestial objects rising in the east and setting in the west is the relative happening. Calculating movements according to relative happenings will yield as good results as when it is done in real happenings. It is like assuming the platform moving backwards as the train goes forward and carrying out your calculations.

The Earth is assumed to be at the centre of the universe. Then all celestial objects, the sun, moon and the stars appear to be on a big sphere with Earth as its centre. This is an apparent sphere of course. But we can assume it and do some mathematical observations. In astronomy this is called the celestial sphere. Relative to the earth’s rotation around its axis the celestial sphere, with all celestial objects in it, would be making one complete rotation around the earth, in the opposite direction, in 24 hours. The axis of rotation will be the same as that of the Earth. Corresponding to the earth’ poles we will also get celestial north and south poles at the points where the earth’s axis meets the celestial sphere.
On this celestial sphere the stars are fixed in their positions. You may have read that stars are really not stationary but in constant motion. But their distances from us are immeasurably great and their motions relatively very diminutive that they have a fixed position on the celestial sphere. Since their positions are fixed we can imagine many shapes among the stars by joining them. These are called constellations.

The whole celestial sphere is divided into 12 equal stripes. Each stripe will have a range of 300 on sky. These stripes are named after the main constellations found in them. These are called the zodiacs. Hence we will get 12 zodiacs viz. Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces.

On the celestial sphere the sun and the planets will be seen to move through the stars in west -east direction. The Sun will go through all the zodiacs in an year, at the rate of 1 zodiac per month. Our ancestral wise mathematicians decided the entry point of the sun into the zodiac sign of Aries as the beginning of the year, since this takes place in the beginning of summer.
This takes place between 13th and 15th of April and is called the Chiththirai Varudap pirappu, Chiththirai being the Tamil name for April. Aries is preceded by Pisces. Since the New year is defined as the entry of the sun into Aries, the eastern most point on the disc of the sun coming into touch with the line of demarcation between the zodiacs Pisces and Aries will be the exact time of the beginning of it.

This time would be for the earth, the whole world. It would apply to every country, each in relation to its time zone. Suppose the New year begins at 1:55 pm, Tuesday 14-04-2015 in Colombo, Srilanka, time in London would be 09:25 am, Tuesday 14-04-2015. At Honolulu, Hawaii, USA it would be 11:25 pm Monday 13 – 04- 2015. It is the same moment for all these places.
We all know that the movement of the sun affects the climate. The seasons spring, summer, autumn and winter are due to this. There are frequent changes in the tides of the seas. The resultant gravitational pull of the sun and the moon as the latter goes round the earth is the said to be the cause of this. Climate affects the behaviour of all living things including human beings. Besides the sun and the moon, the rest of the planets as well affect a number of happenings on the earth.

Natural settings affect our behaviour. Our present behaviour and experience is going to affect our future outlook. Based on this ancient wise men evolved the science of Astrology.

In astrology the effects of the two big planets, namely Jupiter and Saturn are regarded as important. Jupiter goes round the Sun once in twelve years. From the earth it will appear to be in each zodiac every year. Saturn goes round the Sun once in thirty years. From the earth it will appear to be in each zodiac every 21/2 years.
L.C.M. for 12 and 30 is 60. So once in every sixty years both these planets will be seen in the same zodiac. Hence the combined effects of Jupiter and Saturn will have 60 variations on the earth. Accordingly a cycle of 60 years is recognized and they are named. That is how each Tamil year gets its name.