Maria Celeste's letters are the spine of a story usually told without her

Sobel builds her entire account around the 124 letters that survive from Galileo's illegitimate daughter Virginia, who entered a convent at thirteen and took the name Suor Maria Celeste. Galileo's replies to her are lost, likely destroyed after her death, so the correspondence we have is one-sided, filled with requests for food, remedies, and news, alongside expressions of devotion to the father she addressed with formal reverence. Sobel treats these ordinary, unglamorous details as evidence of an intense, sustaining bond rather than mere filial duty.

By centering the book on this asymmetric correspondence, Sobel recovers a woman who has been little more than a footnote in most Galileo biographies, showing her as an active emotional and practical presence in his life during his most dangerous years. She copied his letters, monitored his health, and offered steady support through his trial and confinement.

Takeaway: history's supporting cast often did more sustaining work than the record credits them for.