eta bhāvi' kali-kāle prathama sandhyāya
avatīrṇa hailā kṛṣṇa āpani nadīyāya
eta - thus; bhāvi' - thinking; kali-kāle - in the Age of Kali; prathama - first; sandhyāya - in the junction; avatīrṇa hailā - descended; kṛṣṇa - Lord Kṛṣṇa; āpani - Himself; nadīyāya - in Nadia.
The prathama-sandhyā is the beginning of the age. According to astronomical calculation, the age is divided into twelve parts. The first of these twelve divisions is known as the prathama-sandhyā. The prathama-sandhyā and śeṣa-sandhyā, the last division of the preceding age, form the junction of the two ages. According to the Sūrya-siddhānta, the prathama-sandhyā of Kali-yuga lasts 36,000 solar years. Lord Caitanya appeared in the prathama-sandhyā after 4,586 solar years of Kali-yuga had passed.