Indian lunar calendar, panchanga. A day is measured between sunrises. A month is the period from moon cycles. A lunar month lasts 28 days. A year is measured from the beginning of a season until its return. A lunar year lasts 12 months or 254 solar days. An additional month, adhika is added to the calendar at 5-yearly intervals as a lunar year falls short of a solar year by 12 days. Each month is divided into 2 cycles of the moon. There are 4 seasons in a year, known as “rtu”.