Ephemerides, or the Perpetual Almanac, and the Circuits within them.

The use of these perpetual circuits of the Ephemerides is easily understood by those who have been introduced to them beforehand. Indeed, this Ephemeris displays the true motions of both the luminaries the Sun and the Moon as well as other planets for any time and place, divided into ten integral parts. The Ephemeris for the Sun occupies the first place (since it is the greater luminary), and it comprises four years of revolution. Next, the lunar Ephemeris, extended for thirty-one years of revolution, follows in the second place. The third place is held by the head of the dragon caput draconis the moon's ascending node, containing ninety-three years of revolution. The remaining Ephemerides of the planets follow, extended according to the number of their years of revolution: Venus for eight years; Mercury, with its varied forward and backward motion, for one hundred and twenty-five years; Mars for seventy-nine; Jupiter for eighty-three; and Saturn for fifty-nine years, each claiming its own place in the series. There remain four tables annexed at the end: the first explains the entry of the Sun into the beginnings of the months of the year; the second expresses the years in which conjunctions of the planets usually occur; the third announces the eclipses of the luminaries occurring in certain years; and the fourth table is good and suited for the ascendant and the remaining houses of the sky. Thus, the context of the Ephemerides is completed in twenty parts. All these things are most manifest to anyone looking at the text of the Ephemeris and its inscriptions, which carry the reason for each title at the head above each section. However, we wish "revolution of years" to be understood here in a general sense: namely, the number of all solar years that have passed since the root the epoch or starting point, during which the true motion of the luminaries and other planets, while circling, returns precisely to the same original place in the zodiac on the same year, month, and day, as has been observed by men familiar with the starry houses, according to the numbers of the years of revolution.

For each, as noted above and annotated in order at the top of the individual Ephemerides, it is discovered by those learned in the stars that the motion returns almost exactly to the place from which it began. Above all else, one universal use of the Ephemeris must be noted first. For we have assumed that any Ephemeris, once the solar year of Christ 1472 has revolved, takes its beginning on the last day of February at noon, calculated above the meridian of Toledo. It is necessary to hold this number of years of Christ, namely 1472, as the place of the root—that is, the inception of the years of revolution for each Ephemeris. We shall call that number the "root number" in the following sections.

If, therefore, you desire to know the true motion of any luminary or other planet for some past or future year on a certain day, you must always subtract the root number—that is, 1472, which we will consequently call the "prior years"—from the number of the current or future year of Christ, which we will similarly name "posterior years" in the following sections. The distance that remains declares whether the year is prior or posterior to the root number. And if either of these distance numbers exceeds some revolution of any luminary or planet, as explained by the number above, if you divide that distance number by the number of the complete revolution, the result indicates one or more complete revolutions that have elapsed. Whatever remains will show the current year of the incomplete revolution. We shall call this year your "proposed year" where it comes into use in the following sections. This is common knowledge for understanding each of the Ephemerides. We shall append here in detail how we ought to elicit the true motions of each from any Ephemeris.