Hindu calendar, the panchang is vital in the lives of Hindus calculating dates of festivals, auspicious times & for performing rituals. It was initially based on the movement of the moon found in the Rig Veda, 2nd millennium B.C. In the first few centuries A.D., Babylonian & Greek astronomical ideas reformed the Indian calendar. Since then both solar and lunar movements were considered in calculating dates. Religious festivals & auspicious dates are still decided on the lunar movements.