What is most interesting is that all the possible sources where this topic is discussed - the mythical Puranas like Vishnu Purana, Vayu Purana, the Bhagavatam, along with Bhagavad-gita, literary epics such as Mahabharata and the scholarly works like Surya Siddhanta -- all of them -- agree on the measurements of the duration of yugas, kalpas and so on, with some very minor deviations.I remember when I had to visit New Delhi once somewhere in the year 1998, Prof. Mohan Apte asked me to go to the Indian National Science Academy on Bahadurshah Zafar Marg and buy a copy of Surya Siddhanta for him if they have one. I was lucky to get one there, and while returning managed to read parts of it, although I could barely grasp any of it.
The Surya Siddhanta is a well-known ancient treatise on Astronomy (composer unknown), which is often cited by later Indian mathematicians and astronomers such as Aryabhatta and Varahamihira. The treatise describes the Hindu time cycles in the first chapter itself, based on which the following calculations are done.
1. The Basis of Time – Human Respiration
Surya Siddhanta begins with what is most close to us - our own life. And what make life possible? - respiration.
One respiration is called a 'prana' (also, Life literally in Sanskrit).
60 respirations = 1 nadi.
60 nadis = 1 sidereal day and night = 3600 respirations
So that is the definition of 1 day of man.
30 such days of man = 1 month of man.
12 such months = 1 year of man = 360 days of man.
This is one solar year (a year of man).
This is also called a day of gods.
Why do we need this? Because this is the unit of calculation of time span when it comes to large time spans like the Yugas. If we calculate in Human terms, the numbers become mind-boggling (as what you will see below).
2. Duration of a Caturyuga / Mahayuga (Four Yugas)
Now let us get into calculating the time span of the four yugas.
360 such days of gods = 1 year of gods = 129,600 days of man or 360 years of man.
(1 divine year)
12,000 such years of gods = 1 Caturyuga (also called Mahayuga)
Which is also equal to 4,320,000 years of man.
This Mahayuga is then divided into 4 yugas – Krita (4 parts), Treta (3 parts), Dwapar (2 parts), and Kali (1 part).
What does this ‘part’ mean? It means that in all there are 10 parts (4+3+2+1) and they are occupied by these four yugas. It also means that the Yuga Dharma reduces by a quarter every time a yuga changes – but that is a separate topic in itself – maybe for the next post.
So this one-tenth (1/10th) part of the Mahayuga – which is equal to 432,000 human years – is called a Charana. Thus, there are 10 such Charanas in a Mahayuga and they are divided as below:
years of man
years of gods
Krita yuga (4 parts)
Treta yuga (3 parts)
Dwapar yuga (2 parts)
Kali Yuga (1 part)
This is one Mahayuga (Caturyuga), and is thus made of 4.32 million years of man. That’s one hell of a time span!
Each yuga is an age with specific characteristics, but more about that later, after we finish with our discussion about ‘Time’.