Katharina Kepler is known to historians for two reasons. The first is that she was Johannes Kepler's mother. The second is that in her late sixties she suffered the indignity of a witchcraft accusation and a trial dangerously lopsided against her. She spent over a year imprisoned in harsh conditions, barely escaping torture and execution. Incredibly, she has continued to suffer at the hands of historians. The portrait of Katharina in Max Caspar's epochal biography of her son reduces her to that of an obdurate, gossipy lady, as if her neighbours were perhaps justified in their suspicions. In The Astronomer and the Witch, Rublack has rewritten the history of Katharina's witchcraft trial, of her family's response, and of Johannes's defence. At the same time, Rublack examines important aspects of Johannes's character and philosophy within the context of his family experience.

Katharina spent her life in Württemberg, mostly in Leonberg, a town near Stuttgart. The first two chapters of the book are devoted to that locality. Chapter 1 conveys the outlines of Katharina's life, as well as the specifics of daily life in town, from manual labour to lodging and diet. Such details can be very useful in intellectual history, although they often go missing. Here they also shed light on common accusations levelled against supposed witches: when milk was essential to surviving the harsh winters, riding a family's calf to death or hexing a cow were not only perverse but life-threatening. Chapter 2 describes a more elevated sphere of existence in Leonberg. The town was graced in 1608 with the arrival of the Duchess Sibylle of Anhalt Württemberg, whose husband, Duke Frederick I, had died that year. Frederick had been an ambitious ruler looking to harness new discoveries and technologies of the age. He had collected artefacts from the Americas, overseen building projects and financed an impressive alchemical laboratory. Sibylle brought these interests to Leonberg when she took up residence in the town's castle. She commissioned a new garden and threw herself into alchemical–medicinal work. Distilling medicines and experimenting with herbal cures, as Rublack shows, could dovetail with the civic expectations of a noblewoman, a ‘Lutheran mother to her country’ whose remedies were distributed to the poor (p. 55). In other words, feminine natural philosophy was not always dubious but could be fashioned as a virtuous activity in the Lutheran world. Katharina's own dabbling in herbal mixtures and incantations can be reconsidered in this light.

The second decade of the seventeenth century plunged Württemberg into food shortages and militarization. Soon after Sibylle's death in 1614, the governor of Leonberg oversaw the beheading of several alleged witches. Katharina's troubles began in this period. From here, Rublack's narrative moves deftly from the accusations to the trial. She dismisses the scapegoat theory of the witch phenomenon, at least the naive version where the weakest members of a population were targeted. Katharina was by many measures a success, supporting herself and raising four children to viable adulthood despite a tough lot with her husband, an itinerant soldier who disappeared for good in 1589. While most of the accusations against Katharina seem trite, others (fabricated or not) offer a glimpse of hidden social dread. A seamstress testified that Katharina spoke explicitly about the non-existence of God, about humans dying like beasts, about religion as nothing more than a means of social control. Rublack acknowledges the striking nature of the seamstress's testimony. ‘Witchcraft’, she writes, ‘allowed ordinary men and women in tightly regulated communities to speak about fears so terrifying that they otherwise could never have been voiced’ (p. 162). Yet this raises the question of why such fears needed expression through the extreme physical and psychological violence of the witchcraft phenomenon. The prevalent interpretation of witchcraft in Rublack's study is the one voiced by Johannes, wherein his mother's decades of vulnerability as a widow combined with fears of elderly women, fears which Rublack shows to have been deeply rooted in continental Europe.

Two factors saved Katharina. The first was her mental and physical fortitude. She simply would not crack. The second was that, try as they might, the authorities were unable to gain permission to torture her, this almost entirely thanks to Johannes. Rublack emphasizes the importance of his humanist training and of the social skills he had accrued through years of having to secure patronage. He played dirty when required, shredded weak testimony, intellectually outmanoeuvred the prosecution, and shut them down at the critical moment. His scholarly network in Württemberg served him equally well. Law professors at the University of Tübingen, his alma mater, would give the final say on his mother's fate.

Johannes's natural philosophy, and his general intellectual orientations, are never far from the narrative. Throughout her study, Rublack focuses on a vision of nature common to both Sibylle and Johannes, and possibly to Katharina: nature as generative and beneficial, teeming with life and stamped with the image of God. Kepler's animism or vitalism was first examined systematically in Gérard Simon's Kepler: Astronome, astrologue (1979). More recently, Patrick Boner has studied the coherence and extent of vitalism in Kepler's philosophy. Rublack's reading of Kepler owes much to Boner and to a focus on Book IV of the Harmonice mundi (1618). The Harmonice is by far the Keplerian work looming largest in Rublack's narrative. For one thing, Johannes finished and published it during his mother's legal travails. Questions of character and free will feature prominently in its discussion of astrology, and Rublack claims a strong link between these astrological musings and the trial. Here I am not so sure about cause and effect. Kepler had long been thinking about character, his own and his parents’, as Rublack also acknowledges. Moreover, the principles of his astrology date from many years earlier, from works like the De fundamentis astrologiae certioribus (1602) and the De stella nova (1606). However, Rublack makes a fascinating move by suggesting a connection between Kepler's domestic life and his natural philosophy. The Harmonice is an extremely varied work, but the themes of gender and reproduction are found throughout, even in purely geometrical demonstrations. One could argue, following Rublack's lead, that Kepler's views on women and on the male–female rapport strongly inform the Harmonice. Overall, Kepler emerges in Rublack's portrait not as a retiring scholar but as a man with moderately conservative views about women who was deeply involved in family life, in the lives of his children, wives and extended family.

The book might have benefited from a timeline of Katharina's trial, although a timeline of Johannes's life is provided. Some readers might also wish for a stand-alone bibliography (works referenced are cited in the endnotes). These are quibbles. Rublack's study is a fascinating and important contribution on several levels: as family history, as witchcraft history and as history of natural philosophy. Rublack also presents what may be the most nuanced and sympathetic portrait to date of Johannes in middle age. Finally, the book is marvellously written and features moments of high suspense as the Kepler family battle to save their mother.