http://en.wikipedia.org/wiki/Vedic_timekeeping#TimeReckoning of time among *other entities*:
Reckoning of time amongst the pitrs.
* 1 human year = 1 day of the pitrs
* 30 days of the pitrs = 1 month of the pitrs
* 12 months of the pitrs = 1 year of the pitrs
* The lifespan of the pitrs is 100 years of the pitrs
36,000 human years)
Reckoning of time amongst the Devas.
* 1 human year = 1 day of the Devas.
* 30 days of the Devas = 1 month of the Devas.
* 12 months of the Devas = 1 year of the Devas
* The lifespan of the Devas is 100 years of the Devas
36,000 human years)
The Vishnu Purana Time measurement section of the Vishnu Purana Book I Chapter III explains the above as follows:
* 2 Ayanas (six month periods, see above) = 1 year or one day (day + night) of the devas
* 360 days of the devas = 1 year of the devas
* 12,000 years of the devas = 4 Yugas
Reckoning of time for Brahma.
* 12,000 years of the Devas = 1 day of Brahma (4320,000,000 human years). This day is divided into 10000 parts called charanas. The charanas are divided as follows:
The Four Yugas 4 charanas (1,728,000 solar years) Satya Yuga
3 charanas(1,296,000 solar years) Treta Yuga
2 charanas(864,000 solar years) Dwapar Yuga
1 charanas(432,000 solar years) Kali Yuga
[7]
The cycle repeats itself so altogether there are 1000 cycles of yugas in one day of Brahma.
* One cycle of the above four yugas is one mahayuga (4.32 million solar years)
* A manvantara consists of 71 mahayugas (306,720,000 solar years). Each Manvantara is ruled by a Manu.
* After each manvantara follows one Sandhi Kala of the same duration as a Krita Yuga (1,728,000 = 4 Charana). (It is said that during a Sandhi Kala, the entire earth is submerged in water.)
* A kalpa consists of a period of 1,728,000 solar years called Adi Sandhi, followed by 14 manvantaras and Sandhi Kalas.
* A day of Brahma equals
(14 times 71 mahayugas) + (15 x 4 Charanas)
= 994 mahayugas + (60 Charanas)
= 994 mahayugas + (6 x 10) Charanas
= 994 mahayugas + 6 mahayugas
= 1000 mahayugas
as is confirmed by the Gita statement "sahasra-yuga paryantam ahar-yad brahmano viduH", meaning, a day of brahma is of 1000 (maha-)yugas. Thus a day of Brahma, kalpa, is of duration: 4.32 billion solar years. Two kalpas constitute a day and night of Brahma
* 30 days of Brahma = 1 month of Brahma (259,200,000,000 human years)
* 12 months of Brahma = 1 year of Brahma (3,110,400,000,000 human years)
* 25 years of Brahma = 1 kalpa (77,760,000,000,000 human years)
* 2 kalpas = 1 parardha (155,520,000,000,000 human years) [6]
* 2 parardhas = 100 years of Brahma, the lifespan of Brahma (311,040,000,000,000 human years)
The Vishnu Purana Time measurement section of the Vishnu Purana Book I Chapter III explains the above as follows:
* 360 days of the gods = 1 year of the gods
* 12,000 years of the gods = 4 Yugas
* 1,000 sets of 4 Yugas = a day of Brahmá
* 50 years of Brahma = 1 Pararddham
* 100 years of Brahma = 1 Param
* 4,000 + 400 + 400 = 4,800 years = 1 Krita Yuga
* 3,000 + 300 + 300 = 3,600 years = 1 Tretá Yuga
* 2,000 + 200 + 200 = 2,400 years = 1 Dwápara Yuga
* 1,000 + 100 + 100 = 1,200 years = 1 Kali Yuga
* Alternately, the reigns of 7 Rishis, Indra and Manu = 1 Manwantara = 71x12,000+A (A is not given) = 852,000 years of the gods+A (A is not given)
* 14 Manwantaras = a day of Brahmá
Our current date
We are currently in the 28th kaliyuga of the first day of the 1st year of the shvetavaraha kalpa of the second parardha of Brahma in the reign of the 7th Manu, Manu Vaivasvata. This is the 51st year of the present Brahma and so about 155 trillion years have elapsed since he took over as Brahma.
The current Kali Yuga (Iron Age) began at midnight 17 February / 18 February in 3102 BC in the proleptic Julian calendar.
