Johann Kepler, 1571-1630. Astronomia nova aitiologetos [romanized] : sev
physica coelestis, tradita commentariis de motibvs stellae Martis, ex
observationibus G. V. Tychonis Brahe, jussu & sumptibus
Rvdolphi II ... plurimum annorum pertinaci studio elaborata Pragae ... /
[Heidelberg : G. Voegelinus], 1609.
Of the three laws of planetary motion discovered by Kepler, two were
announced in this book. With these demonstrable laws, such devices as
epicycles, deferents, equants and other efforts to explain planetary motion
were swept away. Copernicus in his computations had referred planetary
motions to the center of the earth's orbit, but Kepler referred them to the
sun itself, thereby paving the way for a real center of force and making
possible the Newtonian celestial mechanics. Kepler concluded that 1.
Planets describe ellipses about the sun in one focus. 2. the radius vector
drawn from the sun to a planet describes equal areas in equal times.
(Heralds of Science, 1955 p. 11)