पृष्ठम्:महाभास्करीयम्.djvu/२७४

ELEVATION OF THE LUNAR HORNS 189 contrary case, take their difference. Then take the Rsine of that (sum or difference). (This is the Rsine of the Moon's true declina- tion).¹ From that calculate the nādis of the ascensional diffe- rence of the Moon. The Moon's true declination is used in finding the radius of the Moon's diurnal circle and the Moon's ascensional difference. The pro- cess is the same as that for the Sun. A rule for the determination of the base (bahu) and upright (koti) to be used in the graphical representation of the eleva- tion of the Moon's horns, when the calculation is made in the first quarter of the month for sunset: 9-12. (Calculate the longitudes of the Sun and the visible Moon for sunset on the day of calculation). By the help of the asus intervening between the Sun and the (visible) Moon always find out, in the manner stated before, the Rsine of the Moon's altitude. Then divide the product of the Rsine of Moon's true altitude (thus obtained) and the Rsine of the (local) latitude by the Rsine of the colatitude: thus is obtained the Moon sankvagra, which is always to the south of the Moon's rising-setting line. Then multiply (the Rsine of) the Moon's true declination by the radius and divide (the resulting product) by the Rsine of the colatitude: thus is ained the so called Rsine of the agrā of the (apparent) Moon lying to the north or south (of the ecliptic). Take their sum (i.e., the sum of the Rsines of the Moon's ankvagra and agrā) when they are of like directions, and the difference when they are of unlike direc- tions. Then reversely add or subtract the Rsine of the Sun's agra. Then is obtained the true value of the Moon's base (bahu). Then Rsine of the Moon's altitude is the upright (koti). The asus intervening between the Sun and the visible Moon are the asus of the oblique ascension of that part of the ecliptic which lies between ¹ This rule occurs also in BrSpSi, vii. 5; ŠiDVṛ, I, viii. 2; Sise, x. 7. It is obviously approximate. A better and more accurate rule occurs in Sisi, I, vii. 3 and 13.