Surya Siddhanta
एकायनगतौ स्याताम् सूर्यचन्द्रमसौ यदा। तद्युतौ मण्डले क्रान्त्योस् तुल्यत्वे वैधृताभिधः॥
When the sun and moon are upon the same side of either solstice, and when, the sum of their longitudes being a circle, they are of equal declination, it is styled vdidhrta.
english translation