Matsya Purana — Soma
अत्यर्थं राजते यस्मात् पौर्णमास्यां निशाकरः रञ्जनाच्चैव चन्द्रस्य राकेति कवयो विदुः //
atyarthaṃ rājate yasmāt paurṇamāsyāṃ niśākaraḥ rañjanāccaiva candrasya rāketi kavayo viduḥ //
Because on the full-moon night (Paurṇamāsī) the Moon—the maker of night—shines exceedingly; and because the Moon delights by its pleasing radiance, poets therefore know that night as “Rākā.”
This verse does not address Pralaya; it explains the sacred naming of the full-moon night, emphasizing the moon’s heightened brilliance and its pleasing effect.
By defining Paurṇamāsī/Rākā, it supports correct observance of time for household and royal rites—such as full-moon vows, donations, and monthly ritual duties that depend on accurate tithi-identification.
Ritually, it clarifies that the full-moon night is called Rākā due to the moon’s exceptional radiance—useful for prescribing Pūrṇimā-based vratas, pūjā timings, and auspicious nocturnal observances.