On the Sixty Years-Samvatsara, also called “Shashṭyabda.”

The word samvatsara, which means the years, is a technical term for cycles of years constructed on the basis of the revolutions of Jupiter and the sun, the heliacal rising of the former being reckoned as the beginning. It revolves in sixty years, and is therefore called shashṭyabda, i.e. sixty years.

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Explanation of the terms samvatsara and shashṭyabda