Matsya Purana — Solar–Lunar Motions
यादृक्पुरस्तात्तपति यादृक्पृष्ठे तु पार्श्वयोः यत्रोदयस्तु दृश्येत तेषां स उदयः स्मृतः //
yādṛkpurastāttapati yādṛkpṛṣṭhe tu pārśvayoḥ yatrodayastu dṛśyeta teṣāṃ sa udayaḥ smṛtaḥ //
As it burns (shines) in the front, so it burns behind and on the flanks as well; wherever its rising is perceived, that, for those observers, is deemed its ‘udaya’—its rising.
This verse is not about pralaya; it defines ‘udaya’ (rising/appearance) in practical, observational terms—wherever the phenomenon is seen to rise is treated as its rising point.
It supports correct observation of directions and visible phenomena, which underlies orderly planning—useful for a king’s civic layout and a householder’s orientation of dwellings, entrances, and daily rites tied to eastward ‘rising.’
In Vastu-oriented practice, ‘udaya’ is treated as a functional, visible reference rather than an abstract absolute—helping determine eastward alignment for building orientation and timing/placement of rites that depend on the perceived rising.