New moon western horizon shortly after sunset and before moonset. A lunation or synodic month is the average time from one new moon to the next. In the J2000.0 epoch, the average length of a lunation is 29.530588 days (or 29 days, 12 hours, 44 minutes, and 2.8 seconds). However, the length of any one synodic month can vary from 29.26 to 29.80 days due to the perturbing effects of the Sun's gravity on the Moon's eccentric orbit. In a lunar calendar, each month corresponds to a lunation. Each lunar cycle can be assigned a unique lunation number to identify it. The
Vṛṣabha the Tamil Hindu calendar. The ancient and medieval era Sanskrit texts of India vary in their calculations about the duration of Vrsabha, just like they do with other months. For example, the "Surya Siddhanta" calculates the duration of Vrishabha to be 31 days, 10 hours, 5 minutes and 12 seconds. In contrast, the "Arya Siddhanta" calculates the duration of Vrsabha to be 31 days, 9 hours, 37 minutes and 36 seconds. The Indian solar month names are significant in epigraphical studies of South Asia. For example, "Vrsabha" month, along with other solar months, are found inscribed in medieval era Hindu