In Chapter 3 of the English edition (page 111), there is a minor scientific error. When discussing the mathematical form of Kepler’s second law, I gave an incorrect definition of the angle beta (called the “eccentric anomaly”). In the Spanish edition, Figure 8 is corrected and beta is properly defined as “the angle between the line of apsides and the line from the center to the point on the major radius circle that is directly vertical of the planet.” The corrected Figure 8 makes the idea clear.