Bharatiya Jyotihshastra (History of Indian Astronomy), translated by R. V. Vaidya v2.c12.s3.82

v2.c12.s3.82

The values of vikṣepa are calculated from the latitudes. Latitude is the distance of a planet from the ecliptic measured along the great circle passing through its pole. The latitude is zero at the node ; *i.e.* the point of intersection of the ecliptic and the planet's orbit ; and it is maximum at the point which is 3 signs away from it. The planetary orbits are not exactly circular. So the planets are not always at the same distance from the centre of their orbits. The Moon revolves round the Earth. Hence, when it is at a distance of 3 signs from the node, although her linear distance from the Earth is not always the same, the angular distance is necessarily so. This is not the case with other planets. They revolve round the Sun. The observer at the Sun's centre will always see the maximum latitudes of the planets to be equal to those of the modern values of vikṣepa ; but these will appear to be smaller or greater to an observer on the Earth. The latitude will appear to vary with the values of their radii vectors, *i.e.* their distances from the Sun's centre and their distances from the Earth. The variation due to the first cause is less than that due to the second. Our astronomers have not taken into account the variation due to the first cause. They have only considered that due to the second. Bhāskarācārya remarks about the ‘vikṣepa’ as follows :—