Joseph, the Rama in Hilchos Shabbos 308 says one use a telescope and even adjust it. The MB says that one is allowed to learn other chochmos on Shabbos and the minhag is to be meikil. Since one does not do things for parnasa on Shabbos, it must mean one can use the telescope and study secular books for their own sake, to satisfy one’s intellectual curiosity.
In addition, when the Rama says one can study B’Akrai, that is a term which is undefinable. There is no shiur. So it is a matter of judgment. As long as it does not surpass his Torah studies, would probably be OK. Second, if it is for parnasa, then even if it does surpass the time for his Torah studies it is OK.