अत्र प्रौढिमुपायातः सूर्यतामेति पावनीम् ।परिणामवशादिन्दुरमावास्यार्कतामिव
In plain words
Here, having come to full maturity, he attains the purifying nature of the sun — as the moon, through the working of its own change, comes, as it were, to the sun's very nature on the night of no moon.