Quotation needed from Blind Watchers, p49, Kepler about himself. Nearsighted, multiple vision. Orbits are ellipses. This is not at all obvious unless you understand high school algebra well.
Equal areas exist in equal times.
For all planets, the annual period squared is proportional to the cube of the distance to the sun. Isaac Newton derived his first principle from these laws after he invented the foundations of calculus. The sun's apparent position is that which it is perceived to occupy through its inequality. The mean position is that which it would have occupied it had not had its inequality. It is therefore very likely that the source of the earth's motion is in the same place as the source of the other five planets' motion, namely, n the sun as well.