LONGITUDE IN TIME 53 the precise instant of their occurrence is observable with more accuracy than that of the first and last contact of the moon with the shadow".¹ Thus, says Nilakantha, "whatever accrues as the difference between (the local times of) immersion (of a lunar eclipse) corresponding to the local and prime meridians is the time due to the longitude (of the local place). This may also be obtained from (the difference between the corresponding times for) the emersion of the lunar eclipse".2 The calculated time is the local time for the place lying at the intersection of the prime meridian and the local circle of latitude, while The difference the observed time is the local time for the local place. between the two is obviously the longitude in time for the local place. Another rule : 8. On any day calculate the longitude of the Sun and the Moon for sunrise or sunset without applying the longitude- correction, and therefrom find the time (since sunrise or sunset), in ghatis, of rising or setting of the Moon; and having done this, note the corresponding time in ghatis from the water-clock. The difference (between the two times), say the astronomers well versed in the tantra (composed by Aryabhata), is (the time of rising at the local place of a portion of the ecliptic equal to the motion-difference of the Sun and Moon corresponding to) the local longitude in time. (From this, the local longitude in time may be easily derived). Let Ø° N. be the latitude and λ° E. the longitude of the local place. Also let T₁ ghatis be the time of sunrise and T, ghatis the time of moonrise at the place in latitude Ø°N. and longitude 0. Then (T₂-T₁) ghatis is the time of moonrise (as measured from sunrise) as calculated from the longitudes of the Sun and Moon uncorrected for the longitude- correction. For those longitudes correspond to true sunrise at the place in latitude Ø°N. and longitude 0. 1 Burgess, E., Surya-siddhanta (English translation), Calcutta (1935), p. 47. 2 Cf. TS, i. 31(ii)-32(i). 3 Rules for finding the time of moonrise are given in Chapter VI.
