In Hinduism, each lunar phase has religious and astrological significance. [1]
The first of these is Amāvásyā (Sanskrit : अमावस्या), the day of the new moon. [2] The third is Pūrṇimā (Sanskrit : पूर्णिमा), the day of the full moon. [3] These two days are called the Pratipada (Sanskrit : प्रतिपदा, romanized: Pratipadā) or Prathama (Sanskrit : प्रथमा, romanized: Prathamā) days. [4] The second and fourth phases (the quarters) are less significant, marking only the midpoints of the Paksha (Sanskrit : पक्ष, romanized: pakṣa), the fourteen days on either side of the full moon. There are two pakshas: the first is the 'brightening' (Shukla) of the moon, as it changes from new to full; the second is the 'darkening' (Krishna), as it changes from full to new. [5]
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 and therefore Amāvásyā 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 Amāvásyā the last day of the lunar month in those places. Many festivals, the most famous being Diwali (lit. 'the festival of lights'), are observed on Amāvásyā.
In Vedic timekeeping, a tithi is a "duration of two faces of moon that is observed from earth". [1] Every day of a lunar month is called tithi.