A weekly feature of Torah Tidbits to help clarify practical and conceptual aspects of the Jewish Calendar, thereby better fulfilling the mitzva of HaChodesh HaZeh Lachem...

This Shabbat we bench Rosh Chodesh Tammuz, which will be on Monday and Tuesday. It is always two days in our fixed calendar, because Sivan (like September, April, June, and November - L'HAVDIL) has 30 days. Tammuz itself always has 29 days.

ROSH CHODESH TAMMUZ Y'H'YEH B'YOM SHEINI U'V'YOM SH'LISHI HABA ALEINU V'AL KOL YISRAEL L'TOVA

How to get this month's Molad without a calendar. Take last month's Molad: Shabbat, 48 minutes 5 chalakim after 12 (noon). It takes the Moon (average) 29d 12h 44m 1p to go through its phases. Of the 29 days, we can ignore 28 days, 4 full weeks, because 28 days after Shabbat 12:48:5 is Shabbat 12:48:5. We want to add theremainder, which is 1d 12h 44m 1p, to the previous Molad. Shabbat and 1 day is Sunday. 12 hours and 12 hours is 24 hours, which is 1 day and 0 hours. That brings us to Monday, 48m 5p after midnight (bet. Sunday and Monday). 44 minutes more is 92 minutes, which are 1 hour and 32 minutes. Add one cheilek and we get the Moladof Tammuz - early Monday, 1 hour, 32 minutes, and 6 chalakim. Fun, no?