Surya Siddhanta
भगणार्धम् रवेर् दत्त्वा कार्यास् तद्विवरासवः। तैः प्राणैः कृष्णपक्षे तु शीताम्शुर् उदयम् व्रजेत्॥
Add half a revolution to the sun's longitude, and calculate the corresponding interval, in respirations : by so many respirations does the moon, in the dark half-month (krshnapaksha), come to her rising after sunset.
english translation