How long is a “year”? That question may not have crossed your mind but it is important, because Parashara (and all others) define planetary eras in years. So unless you know what a year is, you don’t really know how long the planetary eras and cycles are.
To answer this question we must turn to the Surya Siddhanta, the authoritative treatise of astronomical calculations upon which ancient Indian astrology is based. This book defines how the movement of planets and stars defines the passage of time.
In its first chapter, it explains that time has two functions: (1) To create cyclic destruction and creation, and (2) To allow things to happen. The first function cannot be quantified because it is infinite, transcendental and all powerful. In the Bhagavad Gita, the infinite Godhead Krishna says that he himself is identical to that function of time. The second function, which allows events to unfold in sequence, can be measured and is the subject of all astrological computations.
To deal with tiny increments (amurta) like milliseconds Surya Siddhanta calculates time based on the movements the Sun across “atoms” (truti). Milliseconds (thank god!) do not usually concern astrologers, who deal in more ordinary spans of time (murta) like years, months, days, hours, etc. Surya Siddhanta calculates these practical timespans based entirely upon the revolution of the nakshatras through the sky (nakshatra ahoratra), which corresponds exactly to the rotation of the Earth on its axis.
Surya Siddhanta gives three other methods of measuring practical time, correlating them to the main method: the nakshatra ahoratra of the Earths rotation. Here are the definitions of a day and the length of a year in each system. I’ve rounded off the year lengths for simplicity.
|Nakshatra||1 Rotation of Earth||359 days|
|Savana||1 Sunrise to the next||360 days|
|Lunar||1 Moon phase (tithi)||360 Tithis (354 days)|
|Saura||1 Tropical degree of Sun||365 days|
The three ancillary timing systems have specific uses only. Surya Siddhanta defines them in its fourteenth chapter: The Saura calendar based on the Tropical zodiac defines the seasons: equinoxes, solstices, year-halves, and months in relation to the (six) seasons. The Lunar calendar is for religious purposes: holidays, anniversaries, vows, pious deeds, etc. The Savana calendar is practical: deeds that need to be done a certain number of “days” before or after other events use the sunrise calendar of the Savana year. Also computation of which planet rules the day, month, and year follows the Savana system.
Nakshatra time is the primary way of measuring how time allows events to occur in a particular sequence. It is to be used for anything and everything except what is specifically apportioned to the other systems.
What is predictive astrology? It is an artful science of foretelling the sequence of events, portending how events will happen. Therefore what measurement system of time should be used for predictive astrology? The system that is specifically meant for defining how time causes events to unfold in sequence. What system is that? It is Nakshatra time.
Therefore to calculate the duration of planetary eras and cycles you must use Nakshatra time, which defines a year as 359.017 days.
A small element of imperfection is impossible to avoid as a result of our inability to perfectly measure time, and to the fluctuations inherent in time itself. One could say that these imperfects and fluctuations may be the mechanism universal karma uses to accommodate the reality of chaos, chance and uncertainty. Nevertheless, the level of precision and accuracy available is great and amply sufficient, especially if you master the artful science and use the correct time scales (Nakshatra time) in your computations.
The full significance of getting the length of the year exactly right will become clear when you learn how transits work with the beginning of eras.
Note: I have continued the discussion here – Do Your New Discoveries Make Your Old Readings “Wrong?”