The Hindu calendar used in ancient Vedic times has undergone many changes in the process of regionalization, and today there are several regional Indian calendars, as well as an Indian national calendar. Mostly, these are inherited from a system first enunciated in Jyotish Vedanga (one of the six adjuncts to the Vedas, 12th to 14th century BC/BCE), standardized in the Surya Siddhanta (3rd century) and subsequently reformed by astronomers such as Aryabhata (499), Varahamihira (6th centur...
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