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033-The Calendar: Around the World

posted Nov 27, 2013, 4:19 AM by Gregory Taylor   [ updated Nov 27, 2013, 12:14 PM ]
(For Nov 27/13)


Para: Think you know when February 29th, 1600 was?

Cubi: Hey, we've done this schtick before. Hey, Roman Calendar, Julian Calendar, all that, right?

Quinn: Information! Consider that there's different calendars in use even now, on Earth.

CoTangent: And we need to talk about this today because....?

Para: Hanukkah and American Thanksgiving coincide! Kinda. Details below.

Sexi: We'll build to it. Like always.


Para: The Gregorian Calendar - from the Leap Year special - is hardly the only one in use. If you DO use it, you're in the year 2013, continually numbering forwards. But let's instead consider a calendar that uses modular arithmetic!

Cubi: Hey, so, wondering what sort of math that is? Hey, it means at some point we'll stop counting forwards, and cycle back to zero - for example, in mod 5, you would count 0, 1, 2, 3, 4, 0, 1, 2... and so on.

Tangent: Actually, a system of that sort exists in computers - think Y2K. As it is, counting forward by seconds since January 1st, 1970, some electronics may experience memory overflow problems in January 2038.

Quinn: More information! The Chinese Calendar has a cycle of 60 years. Every year is named using two stems. The first component is a celestial stem, chosen from 10 available. The second component is a terrestrial branch - or the 12 animals most people know from place mats in Chinese restaurants.

CoTangent: Wait, 10 and 12 stems would imply a cycle of 120.

Sexi: Aha, nice math. Not the way to count it. As an analogy, consider the celestial stem as numbers and the terrestrial as letters. The counting runs: 1-a, 2-b, 3-c, up to 10-j. Then the first resets. 1-k. 2-l. Then the second resets. 3-a. This means it's impossible to have a 2-a or a Yi-Zi year.

Para: Which is okay, as half the celestial stems are similar. They use wood-fire-earth-metal-water, but double them up, separating running water from standing water, and the like.

Cubi: Hey, if you're reading, see if you can mathematically link this sexagenary cycle to "least common multiples"!

Quinn: Information! While a chinese year has twelve months, each year only has up to 355 days. This necessitates a "leap year" every few years, whereby an entire MONTH is tacked onto the calendar.

Para: As a Gregorian reference, the 'Chinese New Year' will always occur between January 21st and February 21st. It's connected to the new moon, but keep an eye out in 2015, when two such moons occur within that time frame.

Sexi: As a final aside, there is some argument about when the Chinese calendar first began. Most give 2637 BC as the date, though the actual use of zodiac animals came later. 

ArcTan: All of which seems to have no bearing on American Thanksgiving. What's next?


Cubi: Hey, here's a calendar that's been with us since 622 AD! Hey, after all, that's when prophet Muhammed established the first capital.

Sexi: This means the Islamic Calendar began after 0 AD, but before the Gregorian reforms of 1582 AD. We're currently living in 1435 Anno Hegirae (AH), and it's been this year since November 3rd, Gregorian.

Quinn: Again information! We're talking about the Lunar Hijiri Calendar in this case. Twelve months, in a year of up to 355 days, not unlike the Chinese. But no leap months. To align with the moon, the calendar adds 11 days over the span of a 30 year cycle.

ArcTan: Why do you keep saying 'Information'?

Quinn: Cubi gets an inflection, why not me?

Para: Of course, the Islamic "day leaps" aren't enough to keep them in line with the Gregorian, so we can't peg dates here, like we did with the Chinese calendar. That said, there's two key events that many Western calendars mark: Ramadan, the name for the ninth month, and Eid-al-Adha, which occurs during the last month of the year.

Tangent: Right, and I can see now how those dates would gradually migrate backwards through the Gregorian calendar. Come to think, won't there eventually come a time when the Islamic and Gregorian calendars identify using the SAME number?

Cubi: Hey, yes, try to figure THAT one out at home!


Sexi: Now, the Hebrew or Jewish Calendar is lunisolar, like the Chinese. A year is twelve months of up to 355 days, but again, they add an extra month every few years. That said, their year is not aligned with the Chinese.

Para: Also, their calendar days begin at sunset, like the Islamic calendar. We're currently in year 5774, which has been counting since creation. Or, on comparative Gregorian terms, we're looking at a start in 3760 BC.

Quinn: Information! The Hebrew New Year - Rosh Hashana - is observed in their seventh month. This generally occurs in Gregorian September, depending on the new moon.

ArcTan: Stop saying 'Information'! Also, wait, does that mean the Hebrew calendar updates its year... with the start of the seventh month?

Para: Correct. The start of the religious year - Nisan, the first month - occurs (by Gregorian terms) in March or April. But it remains within the same numbered year as the month previous.

CoTangent: Interesting. So is this where we make the connection between American Thanksgiving and Hanukkah - the latter occurring in the ninth month of the Hebrew Calendar? Or, wait, should I have said Chanuka there...

Cubi: Hey, you can't really spell that wrong, it doesn't translate in a single manner.

CoTangent: I thought I was articulating, not spelling.

Sexi: Here's the thing. Chanukkah was declared a Jewish national holiday 2178 years ago, and always occurs on the 25th of Kislev. This year, that's in Gregorian November... meanwhile, American Thanksgiving keeps bouncing around from date to date, depending on Thursdays.

Tangent: As Adam Savage might say, 'There's your problem!'


Para: Ooh. Do you think we've been confusing anyone by constantly saying "American" Thanksgiving?

Cubi: Hey, who cares, people should know there's a Canadian Thanksgiving too. Hey, did you know, Canadians used to celebrate in early November - but in 1957, Parliament shifted the holiday back into October? Hey, they wanted to avoid it ever being the same week as Remembrance Day... that being November 11th.

Quinn: Infor... hm, fun fact?

ArcTan: Tolerable.

Quinn: American Thanksgiving is presently on the FOURTH Thursday of November. That WASN'T always the case, and moreover, the reason for the change is - Christmas Shopping!!!

CoTangent: What now?

Sexi: American Thanksgiving USED to be on the LAST Thursday of November. But in 1939, that meant November 30th. So, to create an extra week of Christmas shopping, in the hopes of stimulating the economy, Franklin D. Roosevelt said Thanksgiving would be November 23rd, 1939.

Tangent: Um. Wouldn't there end up being the same amount of shopping, it merely gets spread out over five weeks instead of four?

Cubi: Hey, don't think like a mathematician, think like a politician.

Para: The upshot was SOME states celebrated the 23rd, and others the 30th. But it gets better. In 1940, the last Thursday and the fourth Thursday were both November 28th. Yet Roosevelt declared Thanksgiving would be the 21st!

ArcTan: Let's go back to talking about global calendars, that made more sense.

Cubi: Hey, it's fine, in 1941 the House put forth a law to say the LAST Thursday would be Thanksgiving.

Sexi: Of course, the Senate amended it to be the FOURTH Thursday before it passed. Despite that, Texas was still celebrating the LAST Thursday as late as 1956.

Quinn: Why is 1956 important, you ask? Information! 1956 is the time previous to today when Hannukah and Thanksgiving coincided! Both were, by Gregorian Calendar, on November 29th, 1956. Sort of.

Tangent: You mean, assuming you lived in Texas. And are counting based on the first candle of Hannukah, not the second - as we are this year, 2013.

Para: For reference, they also coincided on November 28, 1918 and November 29, 1888. Granted, the candle count varies - remember Hannukah starts with sunset tonight, November 27th, whereas American Thanksgiving is tomorrow.

Sexi: Theoretically, the intersection is due to happen again in 2070. Notably, Chanuka is drifting out of November - that's why the dates are becoming less frequent.

CoTangent: Hm. That was interesting. Thank you.

Quinn: Now, with the Thanksgiving holiday dealt with, can we talk Canadian football to counter "American football"? By which I don't mean soccer.

Cubi: Hey, why bother, football's over. Hey, the 101st Grey Cup ran on Sunday.

Quinn: My point exactly.

Sexi: Kind of a one dimensional point, don't you think?

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