Satya Yuga

Satya Yuga, also called Krita Yuga, is the first of the four ages that make up a mahayuga or great age in Hindu cosmology, and it is given a duration of 1,728,000 years, four units of 432,000. The texts describe it as the age in which dharma, right order, stands on all four legs; there is no disease, no falsehood, no need of scripture or of law, no division into castes in some accounts, and human life is enormously long. The scheme is set out in the Manusmriti, in the Mahabharata and in the Puranas, with the Vishnu Purana giving one of the fullest statements. The proportions are the key structural feature: the four ages stand in the ratio 4:3:2:1, so that each is shorter than the last and dharma loses a leg with each, and the whole is an account of decline rather than of progress.

The Bhagavata Purana gives the bull of dharma four specific legs, tapas or austerity, shaucha or purity, daya or compassion and satya or truth, and its account of the decline across the ages names which legs fail first: by the Dvapara Yuga, tapas and shaucha are already diminished, and by the Kali Yuga daya has failed as well, leaving only a bare remnant of satya standing, which is why the present age is described as clinging to truth even as everything else the bull once stood on has been lost. In the Puranic scheme of the ten avataras of Vishnu, the first four, Matsya the fish, Kurma the tortoise, Varaha the boar and Narasimha the man lion, are traditionally placed within Satya Yuga, though the texts are not perfectly uniform on where one age's avatara ends and the next begins.

The four ages are not simply laid end to end. Each yuga is given a twilight before it and a twilight after it, sandhya and sandhyamsa, and in the standard Puranic reckoning each of these is one tenth of the age's own length, with the two together making up one fifth of the total. The figure of 1,728,000 years therefore already contains its twilights: 1,440,000 years of the age proper, with 144,000 before and 144,000 after.

The same proportion applies down the series, so that every yuga is nine tenths body and one tenth twilight at each end, and the ratio 4:3:2:1 holds for the whole periods as well as for their cores. It is a tidy scheme and it is stated as such in the Vishnu Purana and the other sources that give the durations.

The twilights matter to how the ages are described. Decline is presented as gradual rather than abrupt, and the transitions are where the character of one age gives way to the next, which is why the texts can place events at the junction of two ages rather than inside either. The end of the Dvapara and the beginning of the Kali are handled in exactly this way in the traditional accounts of the death of Krishna.

A note on the number itself. Every figure in the scheme is a multiple of 432,000, and 432,000 is 1,200 times 360, so the whole system is generated from the 360-day nominal year of Indian calendrical arithmetic and the ratio 4:3:2:1. Whether that arithmetic was chosen for its properties or arrived at by some other route is not stated in the sources, and reconstructions of its origin are proposals rather than findings.