<Li> Mainly theoretical, presents the principles of spherical astronomy and a list of stars (as a basis for the arguments developed in the subsequent books). </Li> <Li> Mainly dedicated to the apparent motions of the Sun and to related phenomena . </Li> <Li> Description of the Moon and its orbital motions . </Li> <Li> Concrete exposition of the new system including planetary longitude . </Li>

How does an astronomer come up with a new hypothesis