We find Yuga cylces mentioned not only in astronomical works, but also in mythological works in India.
Kali Yuga began on the midnight of 17th Feb 3102 BCE and the duration of this Kali Yuga is said to be 4.32 K solar years. Dwapara is 2*Kali Yuga years. Treta is 3*K Y and Krita Yuga is 4*K Y.
Krita Treta Dwaparascha Kalischaiva Chaturyugam
Divya Dwadasabhir varshai savadhanam niroopitham
Thus an Equinoctial Cycle, Mahayuga is equal to 4+3+2+1 = 10 KYs.
E C = 10 KYs.
A Greater Equinoctial Cycle ( Manvantara ) = 71 Equinoctial Cycles
There are cusps happening in between Manvantaras, each equal to a Krita Yuga in duration. A Krita is equal to 4 KYs or 2/5 of a Maha Yuga. Since there will 15 such cusps happening amongst the Fourteen Manvantaras, they are equal to 15*2/5 = 6 Mahayugas.
Hence 14*71+6 = 1000 Mahayugas = 4.32 Billion Years
Sahasra yuga paryantham
Aharyal brahmano vidu
Ratrim yugah sahasrantham
The Ahoratra vido janah ( The Holy Geetha ).
This is one Cosmological Cycle, called Brahma Kalpa.
Chaturyuga sahasram indra harina dinam uchyathe
From one second, it can be logarithmically shown, upto 10^22 seconds. This is what the above diagram shows. This diagram is by courtesy of Wikipedia.
From 10^0 it goes upto 10^22 seconds. One day of Brahma is 4.32 billion years and 100 years of Brahma therefore is 311.04 trillion years, which is shown logarithmically above.
One Asu is 4 seconds, one Vinadi is 24 seconds and one Nadi is 24 minutes. 60 such Nadis make up one day. This is the Sexagesimal division of a day into 60 Nadis ! In Astronomy, one degree is sixty minutes and one minute is sixty seconds. Hence sexagesimal division is justified ! 365.25 such days constitute a year and Hindu calculation goes upto 311.04 trillion years !
