How many children did Galileo have?

Galileo had three children: Virginia, Livia, and Vincenzo. All three were born out of wedlock to Marina Gamba while Galileo was living and teaching in Padua.

Virginia, born in 1600, became a nun under the name Maria Celeste. She maintained a close correspondence with her father and helped manage practical matters at his household. Livia, born in 1601, also entered religious life as Sister Arcangela. Their illegitimate status made marriage difficult in the social world of early-seventeenth-century Italy, so Galileo arranged convent life and dowries for them.

Their younger brother Vincenzo, born in 1606, eventually received legal legitimacy and became Galileo’s heir. He later married Sestilia Bocchineri. A common mix-up is to confuse Galileo’s three children with his six siblings: he was the eldest child of Vincenzo Galilei and Giulia Ammannati, and three of his siblings survived infancy. Galileo never married Marina Gamba, but the identity and number of his children are well documented.