सिद्धान्तशिरोमणि: गणिताध्याय (भास्कराचार्य - ग्रहगणित, मध्यमाधिकार व स्पष्टाधिकार सटीक)

19 the same as their heliocentric ones will also be clarified in the same adhikāra. The reason why we have termed the Mandocchas as apogees in the case of the Sun and the Moon and as aphelia with respect to the other planets is that the Sun moves round the earth relatively while the Moon directly moves round the earth whereas the remainning planets move round the Sun while the Sun moves relatively round the earth. In other words the Sun and Moon have apogees whereas the remaining planets aphelia. The nodes of the planets are the points of intersection of their orbits with the ecliptic which is the apparent orbit of the Sun. In other words the planetary orbits are inclined to the ecliptic which means that their orbital planes do not coincide with the ecliptic plane. In Hindu Astronomy the Sun, the Moon and also the two nodes of the lunar orbit which go by the names Rahu and Ketu are also termed as grahas along with the other five which are known as Tāra-grahas or planets resembling stars. The etymology of the word ‘planet’ is that it moves amongst stars; in this respect the nine Hindu grahas also moving among the stars are eligible to have the same appellation though it is not permitted in modern astronomy. But the word graha has a different connotation etymologi- cally namely गृह्णातीति वा गृह्यते अनेनेति वा ग्रह : ie that which seizes the fates of men is known as a graha. In the course of this work we use the word graha and planet synony- mously so that we deem the Sun, the Moon and the nodes of the lunar orbit also as planets. When the ancient Hindu astronomers knew by obser- vation that the nodes of the lunar orbit have a retrograde motion, and could also measure their mean motion, they extended the analogy to the nodes of the other planets also, whose motion could not be measured during anybody's life-