Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 6 · Calendar, Muhurta Elements
कालमानं मुहूर्ताङ्गानि च
ग्रहाणां निखिलश्चारो गृह्यते सौरमानतः ।वृष्टेर्विधानं स्त्रीगर्भः सावनेनैव गृह्यते ॥ १११ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 111.
All the movement of the planets is taken by the Sun's measure. The rules for rain and a woman's pregnancy are taken by the civil day alone.
Simple meaning: Planet movement is counted by the Sun, and rain and pregnancy by the civil day.
प्रवर्षणां समे गर्भौ नाक्षत्रेण प्रगृह्यते ।
Rain and the year are counted by the stars. Journeys, marriages, vows and shaving need the moon day and year lord.
पर्ववास्तूपवासादि कृत्स्नं चांद्रेण गृह्यते ।
Fasts and house rites follow the Moon. The sixty-year names follow Jupiter.
तत्तन्मासैर्द्वादशभिस्तत्तदष्टौ भवेत्ततः ।
Twelve months of any kind make a year. Jupiter's average movement gives the sixty named years.