Astronomy > Mysterium Cosmographicum
Johannes Kepler's (1571-1630) Mysterium Cosmographicum (1621), first published in 1597, contains his beautiful but fundamentally flawed attempt to order a Copernican universe by modeling it as a series of inscribed platonic solids. This model is what the text is best known for, but the treatise also contains more fruitful astronomical speculations. In chapter twenty-two, Kepler's second law of planetary motion begins to take shape as the qualitative assertion that planets move faster the nearer they are to the sun. The observation is not only significant because of its relevance to his later work; it is also an important departure from Copernicus' epicycles and Ptolemy's equants. A reprint of Georg Joachim Rheticus's Narratio Prima (1540), the first printed description of Copernicus' model of the universe, is appended to Kepler's treatise.