If full-moon has fascinated the ancient man, new-moon must have induced a sort of anxiety and fear. In the Hindu religion, amāvāsyā or new-moon has been raised to the status of a deity capable of bestowing wealth and valiant sons on the supplicant (vide Atharvaveda 7.79.2).
On this day the moon is not visible from the earth. She is believed to be with the sun (amā = near, vāsyā = living), and is seen only by the sun. Hence the other name ‘darśa’ for amāvāsyā.
Two kinds of amāvāsyās are recognised: sinīvālī when it is mixed with caturdaśī tithi (the 14th day after fullmoon) and kuhū when mixed with pratipad (the 1st day after new-moon). Even these are sometimes referred to as deities who can be supplicated.
One of the well-known Vedic sacrifices, the Darśa, has to be compulsorily performed on this day.
Amāvāsyā falling on Monday, Tuesday or Thursday is considered as especially holy. So also, if it is associated with the nakṣatras as Anūrādhā, Viśākhā or Svātī. Several vratas (religious observances) are recommended to be performed on such days.