July 24, 2020
Happy Leap Year! Well, that’s by the Gregorian calendar, not by the Iranian calendar. And because of that discrepancy, everyone’s birthday will be “off” by a day for the next 12 months.
The discrepancy will be noticeable right away, because the Persian New Year’s Day, the 1st of Farvardin, which “always” falls on March 21, will fall on March 20 this year.
And many printed Iranian calendars are so used to listing the birthday of the Prophet Jesus as the 4th of Dey that they are printed that way for the coming year—even though the 4th of Dey falls on December 24 this year.
The Gregorian and Iranian calendars are mathematically and astronomically identical and they each use a leap day every four years. But they have different ways of accounting for the fact that the year is not exactly one-quarter of a day or six hours longer than 365 days. It is actually 5 hours, 48 minutes and 45 seconds longer. Thus a leap day every four years adds a wee bit too much; it adds an extra day every 128 years or about three days too many every 400 years.
The Gregorian calendar has a simple rule to take care of that. Century years—1700, 1800, 1900, 2000—are leap years only if they are divisible by 400. Thus 2000 was a leap year, but 2100 will not be. That formula gets rid of just enough extra leap days to keep the calendar in synch with the earth’s race around the sun.
The Iranian calendar has a much more complicated formula—but it accomplishes just the same goal in the end. Unfortunately, the differences in the two systems mess up the conversion from one calendar to the other.
In the Iranian calendar, the leap day is inserted every fourth year for about a third of a century, but is then delayed a year—that is, there is a five-year gap between leap days. In simplified terms, every 29 years or 33 years or 37 years (depending on calculations we shall skip), the leap day is delayed for a year. That accomplishes the same thing as the dropping of three leap days every 400 years in the Gregorian calendar.
For much of the lifetimes of many readers of this newspaper, that made little difference. From 1964 through 1992, Gregorian and Iranian leap days fell only three weeks apart. The Westerners added a leap day at the end of February, throwing the calendars out of synch; the Iranians added their leap day three weeks later at the end of the month of Esfand, and everything was back in alignment again for three years, 11 months and one week. Big deal.
But in 1996, the Iranian calendar pushed the leap day ahead a year and everything was out of synch for 13 months until the Iranian leap day was inserted. And, again, from February 29, 2000, to March 21, 2001, the same thing happened. And now from February 29, 2020, through March 21, 2021, birthdays and other holidays will again be off by a day.
This will be repeated every four years until 2028 (1407) when the Iranian leap day will be pushed forward yet an additional year. Then your Persian birthday will fall on one day of the Gregorian calendar for two years running and on the day before for the next two years, before repeating that cycle.
There’s a reason for the complexity. The Persian leap day formula means that Saat-e Tahvil—the exact moment that spring begins—falls within 12 hours of the calendric end of the year in Iran—between noon on the last day of the year by the Persian calendar and noon on the first day of the New Year.
In the United States, the moment spring begins can fall on March 19, 20th or 21st. In fact, this year spring starts at 11:50 p.m. Eastern Time on March 19, which is the earliest (by the Gregorian calendar) that spring has begun in 124 years.
And we are going to see even “earlier” springs for decades to come—in fact, until we drop a leap day at the turn of the next century. Then the moment of spring will return to March 21.
Now, that wasn’t so hard, was it?
