Lunar calendar or crescent moons and others employing detailed calculations. Since each lunation is approximately days (29 days, 12 hours, 44 minutes, 3 seconds, or days), it is common for the months of a lunar calendar to alternate between 29 and 30 days. Since the period of twelve such lunations, a lunar year, is only 354 days, 8 hours, 48 minutes, 34 seconds ( days), purely lunar calendars lose around 11 days per year relative to the Gregorian calendar. In purely lunar calendars like the Islamic calendar, the lack of intercalation causes the lunar months to cycle through all the seasons of
Kanyā by the solar month of Tulā. The Kanya month is called "Purattasi" in the Tamil Hindu calendar. The ancient and medieval era Sanskrit texts of India vary in their calculations about the duration of Kanya, just like they do with other months. For example, the "Surya Siddhanta", dated to c. 400 CE, calculates the duration of Kanya to be 30 days, 10 hours, 35 minutes and 36 seconds. In contrast, the "Arya Siddhanta" calculates the duration of the Kanya month to be 30 days, 10 hours, 57 minutes and 36 seconds. The Indian solar month names are significant in epigraphical