Matsya Purana — Solar–Lunar Motions
अहोरात्रात्पतंगस्य गतिरेषा विधीयते दक्षिणादिङ्निवृत्तो ऽसौ विषुवस्थो यदा रविः //
ahorātrātpataṃgasya gatireṣā vidhīyate dakṣiṇādiṅnivṛtto 'sau viṣuvastho yadā raviḥ //
This is the course of the Sun (the sky-going ‘pataṅga’) as determined through the day-and-night cycle: when Ravi (the Sun) has turned back from the southern direction, he is said to stand at the viṣuva (equinox).
This verse is not about pralaya; it is a technical calendrical/astronomical note defining the Sun’s course and the equinox (viṣuva) as a marker of equal day and night.
By identifying the Sun’s turning and the equinox, the verse supports correct timing for vows, seasonal observances, and state/household rituals that depend on accurate calendrical reckoning (kāla-nirṇaya).
Ritually, equinox/seasonal markers guide the scheduling of yajñas, vratas, and temple festivals; indirectly, such solar-direction knowledge also underpins traditional orientation practices used in Vastu and temple planning.