People seem to be having a lot of questions right now about time and the calendar. A reader writes:
I’ve had frog legs before. Those are pretty good. Tastes like chicken. Days of abstinence last from 12am-12am, right. I’ve always assumed that, but i guess i’m still not completely sure, cuz Sundays start at sundown the previous day, right.
According to the Code of Canon Law:
In law, a day is understood as a period consisting of 24 continuous hours and begins at midnight unless other provision is expressly made; a week is a period of 7 days; a month is a period of 30 days, and a year is a period of 365 days unless a month and a year are said to be taken as they are in the calendar (Can. 202 ยง1).
So you’re right that days are reckoned from midnight to midnight (I’ll set aside the technical issue of whether the day begins at 12:00:00 or 12:00:01 or 12:01:00 or 12:01:01). However, it isn’t quite correct to say that Sunday begins at sundown on Saturday. According to the General Norms for the Liturgical Year and the Calendar:
The liturgical day runs from midnight to midnight, but the observance of Sunday and solemnities begins with the evening of the preceding day (Ia:3).
Sunday, considered as a legal day (per the Code) or as a liturgical day (per the General Norms) is still midnight to midnight, but its "observance" begins late in the day on Saturday. What precisely counts as "observance" seems to be unclear, though it has special prayers in the Liturgy of the Hours and it is possible to fulfill the obligation to attend Mass during the period of "observance."
That period, which begins "with the evening," also is not precisely defined in the current law. Evening isn’t sundown (which varies depending on the time of year and what latitude you are at–in Alaska Saturday may not even have a sundown!), but the law doesn’t say just when it begins. In the absence of that, the matter is somewhat debatable. The commentary on the Code of Canon Law put out by the Canon Law Society of Great Britain and Ireland takes the position that without further specification, evening begins at noon (and, indeed, people often do speak of the afternoon as evening, at least in some places). The new commentary by the Canon Law Society of America takes a different position. It would be nice if Rome gave us further guidance on this, and they may well do so as part of the liturgical renewal begun in the last few years.
Incidentally, what applies to Sunday in this regard also applies to all solemnities (which include the other holy days of obligation, plus a few more).
