Calendar time, when it is done truly right, is a complicated topic. There's a nice book that has way more detail on this than most people actually would want (C

Calendar time, when it is done truly right, is a complicated topic. There's a nice book that has way more detail on this than most people actually would want (Calendrical Calculations, https://www.amazon.com/Calendrical-Calculations-Nachum-Dershowitz/dp/0521702380 https://www.amazon.com/Calendrical-Calculations-Nachum-Dersh...).