1,291. The Other Opinion as to the Length of a Solar Year

Hilchos Kiddush HaChodesh 10:1

According to the view of our Sages that a solar year is shorter than 365 and one-quarter days, there is an opinion that it is 365 days, 5 hours, 997 chalakim and 48 rega. A rega (literally, a “moment”) is a 1/76th of a chalak. According to this calculation, the difference between the solar and lunar year is 10 days, 21 hours, 121 chalakim and 48 rega (abbreviated 10, 21, 121, 48) with no remainder at all at the end of a 19-year cycle. Rather, after each cycle, the solar years and the combination of regular and leap lunar years will align perfectly.

Hilchos Kiddush HaChodesh 10:2

Based on these calculations, there are 91 days, seven hours, 519 chalakim and 31 rega from one season to the next (abbreviated 91, 7, 519, 31). If you know the date and the time that any given season starts, you can calculate the start of the next season in a manner similar to the way that it is done according to the opinion that a year is 365 and one-quarter days. (Refer back to halacha 9:4.)