Bharatiya Jyotihshastra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s9.18

v2.c12.s9.18

Some persons begin to maintain, therefore, that the calculations of even the new almanacs are at times as wrong as those of the Grahalāghava, simply because some of the timings in the new almanacs appear to be incorrect, without caring to consider why they seem to be incorrect. It cannot be argued that the calculations of the new almanacs are erroneous because the times of rises and sets given by them are not sometimes found to be correct. It can be proved from plenty of other evidence that their calculations are correct. The reasons for the failure of such timings are quite different. The main reason for the failure lies in the error in the Kālāmśa adopted. The planetary places as obtained from the Grahalāghava are at present found to be always erroneous to a certain extent. If the rises and sets calculated from it are sometimes found to be true it is merely by coincidence. In order to determine the Kālāmśas for a planet, either the difference in the moments of day to day rises and sets of the sun and the planet should be actually observed and recorded or they should be determined by calculation on the basis of the calculated positions of the sun and the planet. The sun, however, is immediately visible when it comes to the horizon. But the chance of observing the rise or set of a planet lasts for a short time before sunrise or after sunset. But as there is twilight at that time no planet is visible when it is on the horizon; it is visible only when it is somewhat above the horizon. Hence, the difference in the daily rise or set of the planets and the sun cannot be found correctly by actually observing them. Even if it were possible to have some means by which to find them, there was no possibility of people in ancient times possessing fine instruments for measuring time and angles with great precision as at present. Again, in order to find by calculation the difference in times of the day to day rises and sets of the sun and the planets from their positions at heliacal rises and sets, it is necessary that the positions be very accurately known. If it be correct, in other words, if it be accurately known that a particular planet is occupying a certain position or is situated at a particular distance from the sun, the time would be correctly calculated. But we do not think that in those ancient times when the Kālāmśas were determined, the calculation of planets' places used to be extremely minute-in fact, so minute that there would be no room even for the error of a 'pala' in the timing of daily rise and set.