Mnemonic ADU: Sunday (A=1), Wednesday (D=4), Friday (V=6) — the three basic postponement days for Rosh HaShanah.
Question 2
The molad of Tishrei falls on Shabbat after noon (day 7, hour 18). On which day is Rosh Chodesh set?
After noon → postpone to Sunday; but Sunday is ADU → postpone again to Monday. This is a double postponement as explained in Halacha 3.
Question 3
What is the exact threshold for the GaTRaD postponement in a simple year?
Mnemonic G-T-RD: Tuesday night, at 9 hours and 204 chalakim from the tenth hour onward — causing postponement from Tuesday to Thursday.
Question 4
What reason does the Rambam give for the postponement rules?
In Halacha 7, the Rambam explains that the postponements exist because the calculation uses mean motion of the luminaries — the rules approximate the true conjunction, not for the Talmudic reasons about Yom Kippur.
Question 5
What proof does the Rambam bring that postponements are needed due to mean vs. true motion?
Halacha 8: when the molad is on Tuesday night and postponed to Thursday, the moon is often not visible Thursday night or Friday night — proving the true conjunction only occurred on Thursday.