Toward the end of the summer of 1581 as the finishing touches were being applied to Uraniborg, Kirsten gave birth to a son. In a family that to that point consisted solely of daughters, it must have been a great occasion, no matter how elevated the rights and status of Danish women may have been relative to those in other contemporary cultures. After having disposed of his father's name (Otte) and used his maternal grandfather's name (Claus), Tycho now baptized his third son Tyge, after his paternal grandfather. When another son was born in 1583, he was named Jørgen, presumably after Tycho's uncle and stepfather but perhaps after Kirsten's father as well.

Tycho's sons were only the vanguard of a considerable increase in the Brahe household. From at least as early as the planning of the eight-room garret on the top floor of Uraniborg, Tycho had envisioned having a significant number of assistants to work with him. As space, instruments, and time became available to Tycho in the early 1580s, therefore, he began to select collaborators until he accumulated a group of eight to twelve members of varying degrees of permanence and competence. Thanks to the curiosity of an anonymous inmate who compiled a fragmentary list of his fellows toward the end of the 1580s, we can obtain a glimpse of at least the upper half of the spectrum of Tycho's assistants.