Amavasya
Amāvāsyā (Sanskrit: अमावस्या) means dark moon lunar phase in Sanskrit. The word Amāvāsyā is common to almost all Nepalese and Indian languages as most of them are derived from Sanskrit. Ancient Babylonian, Greek and Indian calendars used 30 lunar phases, called tithi in India. The dark moon tithi is when the Moon is within the 12 degrees of angular distance between the Sun and Moon before conjunction (syzygy). The New Moon tithi (called Pratipada or Pratima) is the 12 angular degrees after syzygy. Amāvāsyā is often translated as new moon since there is no standard term for the Moon before conjunction in English.
Meaning of Amāvāsyā
In Sanskrit, "amā" means "together" and "vāsya" means "to dwell" or "cohabit".
In the pūrṇimānta māna Hindu lunar calendar used in most parts of the Indian subcontinent, the lunar month starts on the day following the full moon or purnima and therefore Amāvāsyā always falls in the middle of the month. However, in the amānta māna calendar used in some places, the lunar month starts on the day of the new moon, making Amāvāsyā the last day of the lunar month in those places. Many festivals, the most famous being Diwali (the festival of lights), are observed on Amāvāsyā. Many Hindus fast on Amāvāsyā.