Who knows one hundred seventy-three?
Please cite/link your sources, if possible. At some point at least twenty-four hours from now, I will:
Upvote all interesting answers.
Accept the best answer.
Go on to the next number.
According to Rokeach (excerpt here), the fourth blessing of Musaf on (weekday) Rosh Chodesh contains 173 words. (Though by my count, Nusach Ashkenaz has 174, not counting ולכפרת פשע which is recited sometimes, and Nusach Sefard has even more.)
173 rabbis, headed by the Aruch Laner, protested the Brunswick conference. Source: The Jewish Encyclopedia.