  Six astronomical phenomena are listed and discussed in the section called “Phenomena” — most importantly, that Mercury, Venus, Mars, Jupiter, and Saturn, and the satellites of the latter two sweep out equal areas in equal times with respect to the central bodies of their respective orbits, and their periods vary as the 3/2 power of their mean distances from these bodies.  The ellipse, by the way, is not one of the phenomena. In Phenomenon 3 Newton rules out the Ptolemaic system, just as Galileo had in his Dialogue Concerning the Two Chief World Systems, by appealing to the phases of Mercury and Venus and their absence in the case of Mars, Jupiter, and Saturn to conclude that these five orbits encircle the Sun. But this Phenomenon and all the others are carefully formulated to remain neutral between the Copernican and Tychonic systems. In Phenomenon 4 Boulliau's calculated orbits are treated on a par with Kepler's, indicating that the phenomena do not rule out the possibility that Boulliau's alternative to the area rule is correct. Phenomenon 6 explicitly grants that the area rule holds only approximately for the Moon, with a further remark indicating that none of the phenomena are being put forward as holding exactly. This points the way to the most reasonable reading of all of the phenomena: they describe to reasonably high approximation, but not more than that, the observations of the planets and their satellites made by Tycho and others over a finite period of time — roughly from 1570 to the time of Newton's writing. On this way of viewing the Phenomena, they are in no way contentious or problematic. They leave entirely open not only questions about whether any claims concerning the orbits made by Kepler and his contemporaries hold exactly, but also questions about whether any of these claims hold even remotely in other eras, past or future. The Phenomena are thus not inconsistent with Descartes' insistence that the motions are constantly changing.