Surya Siddhanta
दृक्क्षेपः शीततिग्माम्श्वोर् मध्यभुक्त्यन्तराहतः। तिथिघ्नत्रिज्यया भक्तो लब्धम् सावनतिर् भवेत् ॥
Multiply the drịkshepa (or the sine of the zenith-distance of the nonagesimal) by the mean diurnal motion of the Moon from the Sun, and divide the product by fifteen times the radius: the quotient is the parallax in latitude of the Moon from the Bun.
english translation
dRkkSepaH zItatigmAmzvor madhyabhuktyantarAhataH। tithighnatrijyayA bhakto labdham sAvanatir bhavet ॥
hk transliteration by Sanscript