Surya Siddhanta
क्रान्त्योः समत्वे पातो +अथ प्रक्षिप्ताम्शोनिते विधौ । हीने +अर्धरात्रिकाद् यातो भावी तात्कालिके +अधिके॥
The aspect (pita) is at the time of equality of declinations ; if, then, the moon's longitude, as thus increased or diminished, be less than her longitude at midnight, the aspect is past ; if greater, it is to come.
english translation