There are several sources of information on Yuga of which the most important are the Puranas, the Jyothisha Siddhantas and Mahabharata. What we gather from these is applicable to different contexts of reference on Yuga in other sources. Therefore these three can be taken as the primary sources.
One of the five characteristics of a Purana is to give the details of Time at macro and micro level. These are the foundational theories on Yugas. The Jyothisha Siddhantas are primarily about space and time, and calculation of time. Their authority is paramount of all the sources. Mahabharata has many instances of discussion on Yugas.
The foremost feature gathered from these sources on Yuga is the simultaneous use of two types of Yugas in the past. They are the 5 year Yuga and the Catur Maha Yuga having Krita, Treta, Dvapara and Kali Yuga divisions. Both share a common feature – Yugma or Yugya known as Yuga. Yugma means even. Yugya means yoked or fit to be yoked. There is some evenness and yoking nature in both the 5 year Yuga and the Catur Maha Yuga.
The 5-year Yuga
In this type of Yuga, Yugma (evenness) is attained by matching the sun and the moon. Due to the variations in the speed of these two planets, they do not meet at the same point of the zodiac at the same time every year. Such meeting can happen in the 6th year after expunging two lunar months (Adhika Masa). The five year period is evenly split in terms of stars and tithis in such a way that the initial conjunction of the sun and the moon in the first year is repeated again on the 6th year – which was recognized as a next Yuga of 5 years. Using the inputs from Lagadha’s Vedanga Jyothisha, the 5 year Yuga calendar of the Mahabharata time was derived in Part 3 and is reproduced here.
Figure 40: The 5-year Yuga at the time of Mahabharata
The important feature of this Yuga is that Uttarayana served as the year beginning. The true position of the sun turning towards north was taken into reckoning in the 1st year. When the moon joined this sun, that day was the day of Uttarayana in the 1st year. Only the sun and the moon yoked the year (Yugya). There is no evenness attained with the planets. One must recall the previous part (Part 5) where I pointed out that Prof. Srinivasa Raghavan had erroneously assumed a congregation of all the planets at Uttarayana as a mark of the “Astronomical Yuga”. Readers must rest assured there is no such Astronomical Yuga starting at Uttarayana, mainly because there is no conjunction of the planets except the sun and the moon.
Another feature of this Yuga is that every 7th tithi and the 19th star at the time of Uttarayana in a year become the tithi and the star of the next ayana (Dakshinayana) of the year. This pattern repeats only in the 6th year, thereby bringing in the next Yuga. Based on the tithi and the star in a year, one cannot pick out the position of the sun as Prof. Raghavan had done. He zeroed in on the zodiacal degree by Magha Shukla Ashtami at 317 degrees. The moon would be at 90 degrees from the sun on Ashtami. So he added 90 degrees to that to get the vernal equinox. Moon at Rohini concurred with that, according to him.
If we use the same method for the third year of the 5 –year Yuga calendar on Mahabharata (Figure 30) it was waning Dasami on the day of Uttarayana and the moon was in the star Magha. Where would one get the sun’s position by Raghavan’s method for Uttarayana and the location of the vernal equinox from that? For Magha Krishna Dasami, Uttarayana would begin at 334 degrees (317 added with 17 degrees for 17 days between Shukla Ashtami and Krishna Dasami). Ninety degrees from there the vernal equinox would occur at 64 degrees, i.e at Gemini 4 degrees! This is no way different from the use of the astronomy software to pick out the solstice and the equinox at tropical locations. The learning is that this Yuga cannot be arbitrarily used to locate the Uttarayana. Those wishing to see the display of this Yuga in planetariums, can never realize their wish because the Uttarayana position keeps shifting every year in this Yuga and no astronomy simulator is equipped with the settings needed for this since no ground work has gone into even understanding this knowledge of the Vedic seers.
This 5-year Yuga is not a permanent one either, since the calendar shifts (or re-done) with the shift in the position of the solstice and the equinox. In an average of 66.66 years (Surya Siddhanta average), the sun’s equinoctial position shifts by a degree and with that a new date of conjunction with the moon comes into being. We don’t know how often they renewed the calendar – whether with every degree of displacement or once in a few centuries by adjusting the difference during the time in use, but this was used for all ritualistic and civil purposes. Based on this Yuga, Bhishma calculated that the Pandavas had spent additional days in exile.
This Yuga seems to have been used for calculating one’s life. From a reference in Rig Veda on the sage Dirghatamas that he grew old (or perished) in the 10th Yuga, it is understood that one’s age was expressed in terms of this Yuga. Dirghatamas appearing before Ramayana times, it is understood that this 5-year Yuga was in vogue during Rama’s period. Any research on the date of Ramayana requires the 5 year Yuga calendar of that time as I did for Mahabharata. So far I have located just one hint in Valmiki Ramayana to zero in on the 5 year Yuga configuration of that time which I will work out in another context.
When did the 5-year Yuga begin?
Interestingly this Yuga scale offers a hint for its beginning time. That time is deduced from Mārtanda, the sun that was born as Vivasvan initially (the sun of the current times) but remained inside the egg. It represented a time of insolation after the last Ice Age ended some 13,000 years ago. However after a brief period of insolation for 500 years a mini Ice age set in, due to a comet-fall. This period known as Younger Dryas had the sun looking obscure, dull and gloomy due to the dust particles in the air kicked off by the fallen fragments of the comet. The sun appeared as though it was still lying inside the cosmic egg. This Younger Dryas period lasted between 12,900 to 11,700 BP (BP= Before Present). Regular sunlight started falling on the earth only after this period. This is a scientifically accepted fact.
The obscure sun gained the name Mārtanda – because he was not dead (na mrta) though he was within the egg (Anda). It is also told in Rig Veda that Aditi, the mother of eight Suns brought Mārtanda to spring to life and die again. With one less, she finally had seven suns of which the current sun Vivasvan is the 7th but the 8th son after Mārtanda. (Watch my video here). Once the sun became bright after the Younger Dryas, it became known as Vivasvan and from then onwards the Vaivasvata Manu period began. This was after 11,700 BP.
However Mārtanda was not forgotten. He was made the lord of the Adhika Masa! The Adhika Masa is nothing but a month that is very much present but remains dormant (not counted) much like Mārtanda. By assigning this month to Mārtanda, it is known that this 5-Year Yuga system that incorporates the Adhika Masa must have come into vogue only after the Younger Dryas, i.e. after 11,700 BP!
Dirghatamas and Rama had come up some time after this date.
The story of Mārtanda gives another hint that is of help to us in assigning the time period when the other Yuga scale (Catur Maha Yuga) was conceived. The hint was the birth of the planet Saturn!
The Catur Yuga system
The Catur Yuga system has the Yugma or evenness of all the planets (except Rahu, as one of the nodes would necessarily remain 180 degree away from the other). Jyothisha Siddhantas are the authority for this, in their goal of calculating the planetary orbital periods and their motion around the zodiac in geo-centric perspective. When all the planets joined together, it signaled the beginning of a Yuga. “Gruha sāmānyam Yugam” says Aryabhatiya, referring to the super conjunction of planets marking a Yuga.
This requires the knowledge of all the planets by the time this Yuga system was conceived. Saturn being one among the nine planets of this system, the reference to the birth of Saturn (Sanaiscara) to Chāya and the dull sun Vivasvan (Mārtanda) of the Younger Dryas period, denotes the discovery of the planet Saturn during the gloomy period of Younger Dryas. Perhaps in the backdrop of faint looking stars of that time, the shift in the position of Saturn, that very much looks like a star, could have caught up the attention of the sky watching sages and thus was born the planet Sanaiscara.
A corroborative evidence for the date of this discovery in the mini ice period of Younger Dryas was the birth of two younger siblings to Sanaiscara. The youngest was Tapati, the river that flows down from the Satpura plateau in Madhya Pradesh. The name Tapati stems from ‘tapa’ - meaning warmth. Mul Tapi (Multai) from where it originates is only 2457 feet high, but it must have been snow covered during the Ice age to give rise to Tapati, once warmth descended on this region. (The Himalayas lying further north must have been heavily glaciated at that time, with Ganga still trapped within the Gangotri glacier. Any date for Ramayana before 11,700 BP is therefore absurd due to the absence of the River Ganga). With warmth spreading from the equatorial region to north at the end of the Younger Dryas, Tapati started flowing down. Before this happened, the planet Saturn was discovered.
The Catur Yuga system requiring the knowledge of all the planets, with Saturn being the outer most planet in Vedic astronomy, it must be understood that the conception of the Catur Maha Yuga could not have taken place any time before 11,700 BP. This is a crucial input considering the fact that this Yuga scale calculates 432,00,00,000 years (4.32 billion years) as a day of the Four-faced Brahma and 311,040 billion years as His age.
This calculation has the solar year as the basic unit. This being the year of the sun there can be no doubt about where it begins. Today it begins from Mesha / Aries; this was so in the past, as we had always followed the path laid by the sages. When all the planets except Rahu (ascending node of the moon) congregated at the beginning of Aries, Krita Yuga was born, says Aryabhatiya. At the end of Krita Yuga, all the planets except Rahu congregated at the beginning of Aries, says Surya Siddhanta – by which we deduce that Treta Yuga started with this congregation at the beginning of Aries. By calculating the subsequent beginnings, it is deduced that a similar congregation occurred at the beginning of Kali Yuga! (Read here).
This Kali Yuga was found out to be (computed to be) of a duration of 4,32,000 years.
Every 4,32,000 years, all the planets except Rahu should congregate at the beginning of Aries, is the revelation found out by the sages.
Twice this duration was Dvapara Yuga having 8,64,000 years.
Three times the Kali Yuga duration is Treta Yuga, i.e. 12,96,000 years.
Four times the Kali Yuga duration is Krita Yuga, for 17,28,000 years.
Having known by now, that the computation started only after 11,700 BP - when Vaivasvata Manu himself was not yet born - we can safely assume that Rama was NOT born in Treta Yuga of this scale but only after 10,700 BP. Rama, coming in the lineage of Ikshvaku, the son of Vaivasvata Manu, his time period could only be after this cut-off year of the Younger Dryas.
The congregation of all the planets was yet to happen when the calculations were made by the sages sometime after 11,700 BP. In other words, the Vedic society had NOT lived long for thousands of years to physically see the congregation in the previous yuga of Dvapara which started 8,64,000 years before the start of Kali Yuga. It was hypothetical at the time of calculation, but checked regularly with continuous monitoring of the planetary movements.
This can be said for sure considering the difference in the duration of a day of Brahma given by Aryabhata. While all the other ancient texts say that a day of Brahma is equal to 43,20,000 x 1000 years, Aryabhata has differed by saying that it is 43,20,000 x 1008 years. This must have been based on the speed of the planets observed at his time. This also shows that the planetary speed is not constant, but the sages who had watched generationally must have given the average value. Ever since the computation was done (sometime after 10,700 BP), the experts must have been waiting to see the congregation that was due within a few thousand of years. This conjunction was due during the Mahabharata period!
Perhaps for this reason we often find someone or the other in Mahabharata talking about the nature of these Yugas and what to expect in these Yugas. This anxiety factor was missing in Valmiki Ramayana. Only once we see the expression on the reversal of nature in that Yuga, whereas the rest are found in the Uttara Kanda as a regular description of the four yugas. This one instance was that of Malyavan, the maternal grandfather of Ravana telling Ravana that when Dharma swallows Adharma it becomes Krita Yuga. When Adharma swallows Dharma, it brings out Tishya Yuga!
dharmo vai grasate 'dharmaṃ tataḥ kṛtam abhūd yugam
adharmo grasate dharmaṃ tatas tiṣyaḥ pravartat
Tishya was the name of Kali Yuga, originally given by the sages. Tishya is the other name for Pushya that stands for growth, but the description is that of Adharma flourishing! Before going in to the reason for this name, let me point out what Malyavan said further. He continued to say that when Ravana was going around the world, Dharma was destroyed and Adharma was favored by him. He succinctly implied that Kali Yuga was formed by him wherever he went. This was told in Treta Yuga, when Rama was said to have been born.
Treta Yuga occurred sometime after 11,700 BP. And Kali Yuga was created wherever Ravana went.
So what are these Yuga durations?
How was a Yuga determined within these few thousand years?
If Yugas can fuse with one another, what is the relevance for the start of Kali Yuga identified with planetary congregation?
(To be continued)
 Any Purana has five lakshanas (Characteristics): Sarga (creation of the Universe). Prati-sarga (dissolution and re-creation of the Universe), Vamsa (genealogies of Gods, patriarchs, sun and the moon, Manvantaras (Aeons presided over by Manu in which context Yugas are explained) and Vamsa Carita (accounts of dynasties of different ruling families)
 Rig Veda: 1- 158 – 6 “dīrghatamā māmateyo jujurvān daśame yughe”
 Clark et al (2009) “The Last Glacial Maximum” Science DOI:10.1126/science.1172873
 Brahmanda Purana: 3-59
 Rig Veda: 10-72
 Aryabhatiya: 3-8
 Aryabhatiya: 1. 3-4
 Surya Siddhanta: 1-57
 Valmiki Ramayana: 6-35-14