162 ECLIPSES A rule for finding the drggatijyās of the Sun and the Moon : 23. Obtain the difference between the squares of the (Sun's as also of the Moon's) own drgya and drkkṣepajyā, and then take their square-roots. These (square-roots) are the drggatijyās of the Sun and the Moon.¹ The Sun's drggatijya is the distance of the zenith from the plane of the secondary to the ecliptic passing through the Sun. The Moon's drggatijyā is the distance of the zenith from the plane of the secondary to the Moon's orbit passing through the Moon. In later astronomical literature, the dṛggatijyä is used to mean the Rsine of the altitude of the central ecliptic point (i. e., the point of the ecliptic nearest from the zenith); and the distance of the zenith from the plane of the secondary to the ecliptic is denoted by the term drinatijyā. The rationale of the above rule is as follows: In Fig. 18,³ CS is the ecliptic and K its pole; S is the Sun and Z the zenith; KZC and KS are secondaries to the ecliptic; and ZA is perpendicular to KS. Since the arcs ZC and ZA are perpendicular to CS and AS respectively, therefore (Rsin ZS)³ - (Rsin ZC)², (Rsin ZA)² i.e., (Sun's drggatijyā)² (Sun's dṛgjyā)² - (Sun's drkksepajyā). Similarly, in the case of the Moon. = A rule for finding the time of apparent conjunction of the Sun and Moon: 24-27. Severally multiply the own drggatijyas (of the Sun and the Moon) by the Earth's semi-diameter and divide the products by the respective true distances in yojanas. The quotients (thus obtained) are known as the lambanas (of the Sun and the Moon) in terms of minutes (of arc), etc. Multiply their difference by 60 and divide that by the difference between the true daily motions of the Sun and the Moon. Thus are obtained the ghatis etc. (of the lambana). In the forenoon, subtract them from, and in the afternoon, add ¹ This rule occurs also in SiDV, I, v. 6(i). 2 See infra, p. 165,
