Amāvasyā-Pitṛtarpaṇa: Purūravas and the Soma-Based Ancestral Offering (अमावस्या-पितृतर्पण / सोमतर्पण-विधि)
गृह्यते तु दिवा तस्मादमावास्यां दिवि क्षयाम् / कलानामपि चैतासां वृद्धिहान्या जलात्मनः
gṛhyate tu divā tasmādamāvāsyāṃ divi kṣayām / kalānāmapi caitāsāṃ vṛddhihānyā jalātmanaḥ
Therefore Amāvāsyā is reckoned in the daytime, considering the waning in the heavens. And in these portions (kalā) too there is increase and decrease in the Moon, whose nature is of water (jalātmā).