A sourcesheet shared by Dr. Devora Steinmetz to accompany a shiur on the Winter Solstice in Jewish thought. . . .

We name our daughters on their fifteenth day of life. This is based on Vayiqra 12:1-5, which describes the length of a woman’s period of impurity after childbirth. If she gives birth to a son, she is impure for seven days; if she gives birth to a daughter, she is impure for fourteen days. The passage seems to connect the baby boy’s circumcision on the eighth day to the conclusion of the mother’s seven day period of impurity. (Similarly, Vayiqra 22:27 says that a newborn animal must remain with its mother for seven days, and on the eighth day and onward it is acceptable as a sacrificial offering.) It seems, then, that for the first seven days of a little boy’s life, and the first fourteen days of a little girl’s life, the child and mother are still closely linked, and both remain separate from the larger family and community. Then, on the eighth day of her son’s life, and on the fifteenth day of her daughter’s life, the mother begins to rejoin her family and community, and the child too becomes incorporated as a member of the family and community. That is why a baby boy’s father becomes obligated to circumcise his son only on the eighth day, and why the baby boy first receives his name at his brit milah; it is then that the baby boy becomes a member of the community of Israel. On our daughter’s fifteenth day, we come together as a family and as a community to welcome this new member and to give her a name. . . .