Müller, heiress to the estates of her late husbands, was also the daughter of a successful mill owner.
Her father Jobst initially opposed a marriage despite Kepler's nobility; though he had inherited his grandfather's nobility, Kepler's poverty made him an unacceptable match.
By 1599, however, he again felt his work limited by the inaccuracy of available data—just as growing religious tension was also threatening his continued employment in Graz.
Whilst Copernicus sought to advance a helio-centric system in this book, he resorted to Ptolemaic devices (viz., epicycles and eccentric circles) in order to explain the change in planets' orbital speed, and also continued to use as a point of reference the center of the earth's orbit rather than that of the sun "as an aid to calculation and in order not to confuse the reader by diverging too much from Ptolemy." Modern astronomy owes much to "Mysterium Cosmographicum", despite flaws in its main thesis, "since it represents the first step in cleansing the Copernican system of the remnants of the Ptolemaic theory still clinging to it." Dreyer, J. Portraits of Kepler and his wife in oval medallions In December 1595, Kepler was introduced to Barbara Müller, a 23-year-old widow (twice over) with a young daughter, Gemma van Dvijneveldt, and he began courting her.The information given included advice to farmers on when to plant and harvest crops, advice to leaders on military campaigns, advice on matters of romance, etc.Today we understand how the relative positions of the sun, moon and planets, together with the tilt of the earth on its axis, combine to determine the seasons of the year, the phases of the moon, tides, eclipses of the sun and moon, and so on.Caspar, Kepler, pp. 86–89 Instead, he turned his attention to chronology and "harmony," the numerological relationships among music, mathematics and the physical world, and their astrological consequences.By assuming the Earth to possess a soul (a property he would later invoke to explain how the sun causes the motion of planets), he established a speculative system connecting astrological aspects and astronomical distances to weather and other earthly phenomena.