Bharatiya Jyotihshastra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s5.50

v2.c12.s5.50

He invented the astrolabe with which he used to find the longitudes and latitudes of celestial bodies. No one before him had a correct knowledge of the sun’s apparent motion; and it was he who first compiled tables for calculating sun’s true place; these were not known to anyone before him. He recorded observations of the moon, and appears to have compiled tables for finding the true place of the moon. He recorded observations of planets also. The observations recorded by Hipparchus proved useful to Ptolemy in deducing the correction for moon’s longitude, called “evection” and to establish the rule for finding the planetary motions. It has already been stated that Hipparchus found the longitudes and latitudes of stars. Ptolemy was not skilled in the work of taking observations. He invented the quadrant instrument. It is nowhere mentioned in clear terms how all these astronomers used to find time. It appears that they used to measure time by the shadow instrument and the clepsydra (‘ghaṭī’ instrument). Sometimes they used to record what part of the ecliptic was transiting the meridian at the time of taking observations. The Arabs did not bring about any appreciable improvement in the instruments of observation; however, their instruments of observation used to be larger and better than those of the Greeks. The astrolabe used by them was much more complicated.