What does the domenical letter for the year mean? I see it in my farmer’s almanac.
When you are calculating from the March equinox of March 21, in the almanac, Golden Number refers to what the year falls into in the 19 year cycle, and the Dominical Letter tells us what days are Sundays. (comes from the Latin for Dominus/Lord/ Lord’s day). They run A through G, and the days of the year are given those letters starting with January 1st. A year with a Dominical Letter A means that January 1st was a Sunday, and each subsequent day lettered A will also be a Sunday. A year that starts on a Monday, will not have a Sunday until we get the to the letter G, the Dominical Letter for that year. Since the length of the year, 365 days, is exactly 52 weeks and 1 day, we have the basic simple rule that if a Sunday falls on a certain calendar date one year, it falls on the date of the previous date the next year.
The calendar for the Latin Church traditionally includes a lunar calendar within it. The Litterae Dominicales are used to calculate the lunar cycle. I find it quite confusing to be honest.
See this article from the Catholic Encyclopedia for more detailed info.