The Moon takes about 29.5 days to go around the Earth. This is known as lunation or lunar month.

On the New Moon day the Moon is not visible; the day after New Moon is the first day of Sukla Paksha; then 2nd, 3rd and so on, until the 14th , followed by the Full Moon. It is then followed by Krishna Paksha 1st, 2nd and so on, until the 14th, followed by the New Moon. These days are named “Prathama”, etc. as listed below and are known as the tithis of a particular day. The Lunar month, observed in Andhra, Karnataka, etc. States of India, and by Muslims all over the world, begins on the first day after the New Moon.