Bharatiya Jyotihshastra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s9.28

v2.c12.s9.28

These considerations about the factor of altitude and the author's own experience at Barsi (lat. 18° 13') have convinced him that the kālāṃśas mentioned in our old works were determined in our own country. As for kālāṃśas of Ptolemy it can be easily seen that they had no connection whatsoever with our works. On the contrary it can be said about Ptolemy's kālāṃśas that they had not been determined through experience, or if determined, the positions of planets on which they were based were erroneous, else he might have committed some other error. The kālāṃśas of Mars, Mercury and Venus do not amount to anything less than 16°, 12°, and 8° at 18° north latitude. These must therefore, be greater at Alexandria (latitude 31° 13'N). Hence, it follows that the kālāṃśas of Mars, Mercury and Venus mentioned by Ptolemy as 14½°, 11½°, and 5⅝° are considerably wrong. The kālāṃśas for rise and set, as also the altitudes, true for a particular place can be determined with precision. Even when they are so determined, the experience regarding kālāṃśas will be found to vary because of moon light, the reddish light seen at times near the horizon and the relative strength of the observer's eye-sight*. The clouds too serve as another obstructive factor. Hence, it was proper that our authorities on Dharmaśāstra have recommended the omission of few days after and before the mathematically obtained days of planets' rises and sets, because of 'childhood' and 'old age of the planets.