Matsya Purana — Solar–Lunar Motions
एवं गतिविशेषेण विभजन्रात्र्यहानि तु अजवीथ्यां दक्षिणायां लोकालोकस्य चोत्तरम् //
evaṃ gativiśeṣeṇa vibhajanrātryahāni tu ajavīthyāṃ dakṣiṇāyāṃ lokālokasya cottaram //
Thus, by these particular modes of celestial motion, one determines the divisions of nights and days—along the southern course called Ajavīthī, and also the northern region of the Lokāloka (the boundary-mountain separating the worlds from the outer darkness).
Indirectly, it presents the ordered cosmic structure—celestial motions and the Lokāloka boundary—that remains a standard framework for describing the universe even when Puranas discuss creation and dissolution cycles.
By grounding time (day/night) in cosmic order, it supports correct calendrical reckoning for governance and household rites—timing of duties, vows, and rituals depends on proper knowledge of day-night divisions.
Ritually, it points to time-direction principles: many rites require orientation (north/south) and correct timing (day/night). While not a direct Vastu rule, it underpins the calendrical and directional logic used in temple and ritual scheduling.