Contrary to the Ptolemaic cosmology of the original book by his father, the appendix featured a detailed discussion of the controversial and still poorly known Copernican heliocentric model of the Universe.
I motsats till faderns text om Ptolemaios’ system, så innehöll appendixet en utförlig diskussion om den kontroversiella och ännu föga kända Kopernikus’ heliocentriska modell av universum.