Amāvasyā-Pitṛtarpaṇa: Purūravas and the Soma-Based Ancestral Offering (अमावस्या-पितृतर्पण / सोमतर्पण-विधि)
सुषुम्णाप्यायमानस्य भागं भागमहः क्रमात् / कलाः क्षीयन्ति ताः कृष्णाः शुक्ला चाप्याययन्ति तम्
suṣumṇāpyāyamānasya bhāgaṃ bhāgamahaḥ kramāt / kalāḥ kṣīyanti tāḥ kṛṣṇāḥ śuklā cāpyāyayanti tam
As he is nourished through Suṣumṇā, the kalās wane portion by portion in the course of the days—those are the dark (kṛṣṇa) phases; and the bright (śukla) phases replenish him.