अधोलोकवर्णनम् (Adholoka-varṇana) — Description of the Lower Worlds and Cosmographic Measures
सूर्येण विषुवं विद्या त्कालं सोमेन लक्षयेत् / समा रात्रिरहश्चैव यदा तद्विषुवं भवेत्
sūryeṇa viṣuvaṃ vidyā tkālaṃ somena lakṣayet / samā rātrirahaścaiva yadā tadviṣuvaṃ bhavet
The Viṣuva is known by the Sun, and its time is marked by Soma, the Moon. When night and day are equal, then the Viṣuva occurs.