Lunar, Solar, Lunarsolar

 Today is the Chinese new year. It is a sort of floating occurrence because the Chinese calendar is lunar. A lunar calendar is a wackadoodle way to keep track of time.

The basic problem is that the synodic months is about 29 1/2 days long, and that doesn't fit evenly into a year. You get about 354 days if you count up 12 of them, and 383 and change if you do 13. Plus, the Moon's orbit precesses like crazy.

So more properly, the Chinese and Jewish calendars are not lunar but lunisolar. They are basically lunar, but depending on what year it is you've got some 11 or 12 days of slop built in. The usual approach is to sprinkle days of no certain month (called intercalary days) to true it up, more or less, with the seasons. Intercalation is an inexact art, however, so Passover wanders sort of randomly around early Spring. And since the Last Supper was a Passover supper, Easter follows it around like a tiny dog.

A solar calendar is better since if you follow the Sun you necessarily follow the seasons. But that started off in wackadoodleland as well. The Roman calendar was basically solar, but it only had 10 months, beginning on the Vernal Equinox. Winter was left as an uncollated expanse of monthless days. Months were reckoned according to the first of the month (the kalends), a day shortly before midmonth (the ides), and eight days (definitely not 9) before called the . . . nones? These terms belie the origins of the Roman calendar in an observational lunar one, as they correspond to the first sighting of the crescent Moon (kalends), the first quarter Moon (nones), and the full Moon (ides).

Eventually January and February were added to the calendar (kalendar), but the system still required constant maintenance as it ran well short of the solar year. For superstitious reasons, intercalation was always added to February as it was an unlucky month, even after it was no longer the last month of the year, to keep religious observances in their proper months. But they would save up days until they could stick a whole entire intercalary month between February and March. So ordinary years were 355 days long, with periodic bursts to 377 or 378, and an average of 366 1/4 over four years. Later, the intercalation was revised to give an average year of 365 1/4 over 24 years.

On top of that, intercalation was subject to the political winds. It was determined by religious officials, the pontifices, and since the terms of Roman politcal offices generally corresponded to the years, the power of the pontifice was obviously prone to abuse, lengthening or shortening years depending on who was in power. In time of war, particularly the Punic Wars and the Civil Wars, intercalation was less of a worry than survival, and the year could get seriously out of sync with the tropical year as a whole stream of intercalary days were omitted.

The upshot is that the average Roman citizen generally had no idea what day it was, and depending how far they were from the city, neither did Roman officials.

In 46 BCE, Julius Caesar, late returned from Gaul on the other side of the Rubicon, determined to straighten out the mess. He summoned forth a committee which eventually decided to satisfy no one by merging the old Roman months with the fixed length of the Egyptian calendar (365 days but who cares much in the desert?) and the determination by Eudoxus of Cnidos that the tropical year (the cycle of seasons) was 365 1/4 days long. Officially, this calendar applied only to the city of Rome but come on! Anyone doing business with Rome, which was the same thing as anyone at all, needed to be on the same page.

This is how leap year came about. It was an intercalary day inserted every four years to true up the Julian calendar with the tropical year. It worked pretty well for a pretty long time except for one problem -- the tropical year is actually 365.2425 days long. So the Julian calendar was lazily running ahead of the tropical calendar, with the net result that Easter was marching slowly backward into February. By the time of Bede, in the 8th century, it was already 3 days off, and by the time of Pope Gregory in the 16th century, it was 10 days off.

The solution was relatively simple. If it is a century year, skip the leap year. Sort of subtracting an intercalary day. Thursday 4 October 1582 was declared to be followed by Friday 15 October 1582. This system is amazingly accurate. We won't have to true it up with an intercalary day until 4612 CE.

Trouble is that events around that time had produced the Reformation, and Protestants viewed with deep suspicion any attempts to mess with time emanating from the Vatican. The UK did not change over from the Julian calendar until 1752. By that point, it was 11 days out of sync. People like George Washington and Thomas Jefferson calmly adjusted their birthdays accordingly, but the great unwashed believed that the Pope had shortened their lives by 11 days and they wanted them back. Riots ensued.

This makes it fiendishly difficult to pin down when things happened between the mid-16th century and the mid-18th century. Astronomers have thrown up their hands and use Julian Day Numbers instead. Julian day 1 occurred on January 1, 4173 BCE and numbered sequentially from that point forward regardless of calendar. That date was chosen because (a) it is before any precisely datable historical event, and (b) numerology. It is the date in the past when the solar cycle (28 years long, having to do with leap years), the lunar cycle (19 years, when the phases of the Moon recur on the same day of the year) and the indiction cycle (15 years, having to do with tax collection but for some reason pegged to the Egyptian calendar which began on the first day of Thoth) were in their first year together.

But back to lunar calendars. The Chinese calendar, as previously noted, is not truly lunar since it is adjustable to keep up with the tropical year. But the Islamic calendar is lunar through and through. It is 12 lunar months long, lasting 354 or 355 days. That is due to the prohibition of the nasi recorded in the Qur'an, Surah At-Tawbah (9):36–37 where we read:

" Know that intercalation (nasi) is an addition to disbelief. Those who disbelieve are led to error thereby, making it lawful in one year and forbidden in another in order to adjust the number of (the months) made sacred by God and make the sacred ones permissible. The evil of their course appears pleasing to them. But God gives no guidance to those who disbelieve. "

So. No intercalation. The Islamic calendar is not only a lunar calendar, but an observational lunar calendar. It does not matter when things begin. It matters when they are observed to have begun. It is rather like telling time with a sundial and simply striking rainy days from the ken of men. So each month begins when someone with a following actually sees the first crescent Moon. If there are clouds, it hasn't started yet. These men then testify to a committee and everyone can start the new month. This means that the calendar (and all its itinerant feasts, fasts, pilgrimages and holidays) is longitude-dependent. The calendar in Western Muslim countries is out of sync with the same calendar in Eastern Muslim countries by a day or a bit more.

I once had a Muslim following. When I was in graduate school, I did my teaching assistantship in an astronomy program. Some time in the spring, we would start getting these mysterious phone calls -- "Can you see the Moon yet?" It was more salient then than the other months since it would mean the end of Ramadan and they could start eating again. But I didn't know that at the time. So I would say "Well, the New Moon was 3 days ago so yeah, probably someone can." And they would reply "But has it been seen yet?" And I would reply "Erh?"

It took a while to work out what was going on, but now you know. And in point of fact, for any purpose not involving religion, Muslims use the Gregorian calendar. Business continues apace, whether you can see the Moon or not.

And the truth is that due to its tidal interaction with the Moon, the Earth speeds up and slows down all the time, so the idea of a fixed number of days in the year is simply not truly viable.

So do what you want. I'm gonna say it is the first day of Epiphi in the year 4909, Sothic year 4.

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