Islamic calendar lunar months begin precisely at the time of the monthly "conjunction", when the Moon is located most directly between the Earth and the Sun. The month is defined as the average duration of a revolution of the Moon around the Earth (29.53 days). By convention, months of 30 days and 29 days succeed each other, adding up over two successive months to 59 full days. This leaves only a small monthly variation of 44 minutes to account for, which adds up to a total of 24 hours (i.e., the equivalent of one full day) in 2.73 years. To settle accounts,
Karkaṭa followed by the solar month of Siṃha. The Karkata month is called "Adi" in the Tamil Hindu calendar. The ancient and medieval era Sanskrit texts of India vary in their calculations about the duration of Karkata, just like they do with other months. For example, the "Surya Siddhanta" calculates the duration of Karkata to be 31 days, 11 hours, 24 minutes and 24 seconds. In contrast, the "Arya Siddhanta" calculates the duration of the Karkata month to be 31 days, 11 hours, 13 minutes and 36 seconds. The Indian solar month names are significant in epigraphical studies of South Asia.