New. German language limited edition of 100 copies. Includes the foreword to the 1939 edition by Max Caspar. 403 pages.
About the "Harmonice Mundi" (Weltharmonik):
While medieval philosophers spoke metaphorically of the "music of the spheres", Johannes Kepler discovered a physical harmony in planetary motion. He found that the difference between the maximum and minimum angular speeds of a planet in its orbit approximates a harmonic proportion. For instance, the maximum angular speed of the Earth as measured from the Sun varies by a semitone (a ratio of 16:15), from mi to fa, between aphelion and perihelion. Venus only varies by a tiny 25:24 interval (called a diesis in musical terms).
The celestial choir Kepler formed was made up of a tenor (Mars), two bass (Saturn and Jupiter), a soprano (Mercury), and two altos (Venus and Earth). Mercury, with its large elliptical orbit, was determined to be able to produce the greatest number of notes, while Venus was found to be capable of only a single note because its orbit is nearly a circle.
At very rare intervals all of the planets would sing together in "perfect concord". Kepler reminds us that harmonic order is only mimicked by man, but has origin in the alignment of the heavenly bodies.