Matsya Purana — The Attendant Hosts of the Sun and Moon: Monthly Gaṇas
अमावास्यां तथा तस्य अन्तरा पूर्यते परः वृद्धिक्षयौ वै पक्षादौ षोडश्यां शशिनः मृतौ एवं सूर्यनिमित्ते ते क्षयवृद्धी निशाकरे //
amāvāsyāṃ tathā tasya antarā pūryate paraḥ vṛddhikṣayau vai pakṣādau ṣoḍaśyāṃ śaśinaḥ mṛtau evaṃ sūryanimitte te kṣayavṛddhī niśākare //
On the day of amāvāsyā, the new moon, that orb is, as it were, filled again in the interval thereafter. Indeed, waxing and waning occur at the beginning of the two fortnights; and on the sixteenth portion the Moon is said to ‘die’, that is, to disappear. Thus, with the Sun as the determining cause, the Moon undergoes decrease and increase.
It does not describe Pralaya directly; it explains cyclical cosmic rhythm through lunar waxing and waning, presenting time (tithi/pakṣa) as an ordered, law-governed process.
By defining amāvāsyā, pakṣa, and the Moon’s phases as Sun-determined, it supports correct calendrical observance—helping householders and rulers time śrāddha, dāna, vrata, and state rituals according to proper tithi and fortnight.
Its primary significance is ritual timing: amāvāsyā and pakṣa-based reckoning governs when offerings, fasts, ancestral rites, and other ceremonies should be performed in accordance with the Matsya Purana’s dharma-oriented calendar.