Zompist Bboard Again

I just came up with the basics of a possible calendar for a conculture here on our Earth, and I want to post it while it's still fresh in my mind.

The advantages of this calendar would be that it keeps the year roughly aligned with the seasons, doesn't require any math more advanced than the ability to count to at least 366, and still keeps a role for the Moon. Please tell me if you know of any other calendar that meets all three of these conditions.

The idea is that each year is either 365 days long - a "short" year - or 366 days long - a "long" year. No two "long" years may follow each other, but a "short" year may be followed by either a "long" year or another "short" year.

At each New Year Festival - I haven't decided when that is yet - if the year that's ending is a "short" year, the Appropriate Authorities determine whether this New Year Festival appears to be "early" or "late" compared to when it's "supposed" to be. The Appropriate Authorities may be scholars, or priests, or shamans, or community elders, or some other specialized group. In a very egalitarian community, the Appropriate Authority might even be a meeting of all adult community members.

In any case, the determination whether the New Year is "early" or "late" is made either based on astronomical observations or, if that's too fancy for the community in a specific time and place, based on simply observing the weather. If the New Year is "late", the year that's starting is announced to be a "short" year, while if it's "early", the year that's starting is announced to be a "long" year.

Now, for practical purposes, some people might want intervals longer than days but shorter than years. For them, there are Heaps of Days, roughly equivalent to months. Each year has twelve "regular" Heaps of Days and one shorter Heap of Days at the end.

At each New Year Festival, the Appropriate Authorities announce how many days have passed since the most recent New Moon. Then, for the rest of the year, each Heap of Days starts as many days after the most recent New Moon as the year itself had started after the most recent New Moon. To avoid trouble in times and places where the weather might be too bad to reliably observe the New Moon, and where it might also be difficult or impossible to communicate quickly with other places that have better weather, there's an additional rule that under such circumstances, a Heap of Days may not be longer than 30 days.

I think this calendar would nicely avoid the pitfalls of many calendars throughout history which either ignored or partly ignored the Moon, or ignored the seasons, or did fairly complicated stuff like leap months.

A possible historical development is that, if a culture becomes more centralized, and it becomes more important to keep New Year Festivals and beginnings of Heaps of Days in synch over a large area, at each New Year Festival, a central authority makes the two traditional announcements not for the year that's starting, but one year in advance. Even later, it might become the norm to use astronomical calculations to determine starts of years and Heaps of Days many years in advance. Cue acrimonious schisms...

What's the calendar for?

If you only want to plant in the right season, there might be no downside to ignoring the moon.

If you mainly want to determine festival days, there might be more spiritual resonance if you had the same number of days every year. Mesoamerica had a special 260-day ritual calendar.

rotting bones wrote: ↑Sat May 16, 2026 1:45 am What's the calendar for?

If you only want to plant in the right season, there might be no downside to ignoring the moon.

If you mainly want to determine festival days, there might be more spiritual resonance if you had the same number of days every year. Mesoamerica had a special 260-day ritual calendar.

Mostly practical stuff: telling people when to do things that need to be done at a certain point in a specific season in order to work. Stuff like that. But I still try to acknowledge that the Moon matters to a lot of people, and that many people seem to find it useful to have some kind of subdivisions of the year.

Dunno about "there might be more spiritual resonance if you had the same number of days every year". Doesn't seem to be the case with the traditional Christian, Chinese, Islamic, or Jewish calendars.

Raphael wrote: ↑Sat May 16, 2026 7:22 am

rotting bones wrote: ↑Sat May 16, 2026 1:45 am What's the calendar for?

If you only want to plant in the right season, there might be no downside to ignoring the moon.

If you mainly want to determine festival days, there might be more spiritual resonance if you had the same number of days every year. Mesoamerica had a special 260-day ritual calendar.

Mostly practical stuff: telling people when to do things that need to be done at a certain point in a specific season in order to work. Stuff like that. But I still try to acknowledge that the Moon matters to a lot of people, and that many people seem to find it useful to have some kind of subdivisions of the year.

Dunno about "there might be more spiritual resonance if you had the same number of days every year". Doesn't seem to be the case with the traditional Christian, Chinese, Islamic, or Jewish calendars.

The early Roman calendar predating scientific tinkering reportedly had 304 days in a year: https://en.wikipedia.org/wiki/Roman_calendar

The slight variation in the number of days in most calendars is necessitated by the fact that no celestial revolution matches a specific number of days precisely. E.g. The Islamic calendar is purely based on moon sightings IIRC. The traditional version doesn't have leap periods. (For combined systems, different celestial bodies don't match each other's orbits either.)

The question is, in what way are celestial orbits relevant to spiritual resonance in your society? Do they believe the sun orders cosmic harmony in a way that needs to be reflected in a spiritual calendar? Based on what you say, your culture might attribute some spiritual significance to the moon.

if that's too fancy for the community in a specific time and place, based on simply observing the weather.

Without astronomical obervations, years may pass until people notice that the New Year (or other points, like swallows returning or the first snow or whatever) are really "off". So if you would like to return to the old synchronicity, you'd have to intercalate several leap days or to have several long years in a row.
But astronomical events like the equinoxes or longest and shortest days of the year are not too difficult; as far as we know, people already did that in the Neolithic.

hwhatting wrote: ↑Mon May 18, 2026 4:38 am

if that's too fancy for the community in a specific time and place, based on simply observing the weather.

Without astronomical obervations, years may pass until people notice that the New Year (or other points, like swallows returning or the first snow or whatever) are really "off". So if you would like to return to the old synchronicity, you'd have to intercalate several leap days or to have several long years in a row.
But astronomical events like the equinoxes or longest and shortest days of the year are not too difficult; as far as we know, people already did that in the Neolithic.

Thank you, good to know!

OK, I've now worked out something much more elaborate roughly based on this calendar, suitable for used in science fiction set in a future Earth. (That is, if the writers aren't worried about confusing the audience with a mostly new calendar.)

I might integrate it into my Semi-Utopian Future Earth Scenario described here https://www.verduria.org/viewtopic.php?f=3&t=1335, but I'm not sure about that. First, I already quite like having the main story in that scenario tied to the Gregorian year 2573; second, I don't like confusing the audience with a fictional calendar and especially a fictional counting of year; and third, I've already written the Gregorian and Islamic calendars into the Constitution of Earth in that scenario. But who knows; I might change my mind about about any of these things.

This full-fledged calendar has secular, Western Christian, Islamic, and a few Chinese and African elements.

In keeping with my sometimes a bit dry and law-oriented tendencies, I've written this up as a fictional Act of Parliament of the United Earth. Comments by me on specific provisions are labelled as "calendar designer's remarks", and are put in italics.

CALENDAR, TIMEKEEPING, AND MERIDIAN REFORM ACT

Title 1 - General Provisions

Section 1

This Act establishes a new calendar system, to be known as the Unified Reform Calendar; a new system system of timekeeping for days, hours, minutes, seconds, and timezones, to be known as Unified Reform Time; and a new system of meridians of longitude on Earth, to be known as the Unified Reform Longitude System.

Section 2

In this Act, "Meridian Astronomical Reference Point" shall refer to the Merdian Astronomical Reference Point defined by Section 2 of Title 2; "Calendar Astronomical Reference Point" shall refer to the Calendar Astronomical Reference Point defined by Section 2 of Title 3; and "Old System" shall refer to the system for determing various aspects of timekeeping traditionally used in many places at the time of the enactment of this Act, consisting mainly of the Papal Bull Inter gravissimas, issued in the year 1582 of the Old System, and of the divisions of Earth into timezones determined relative to the Greenwich Merdian, as proposed at the International Meridian Conference of the year 1884 of the Old System.

Calendar designer's remark: The Institutions of the United Earth are a bit less strict on the seperation of state and religious matters than, for instance, the French laicists or US liberals of our time, and therefore, they don't have much of a problem with directly referencing religious documents or matters in the official text of Acts of Parliament. I guess for each of the two main references to something religious, I could, theoretically, rewrite the text so that it means the same thing while no longer directly containing a religious reference, but, frankly, I'm too lazy for that right now.

Section 3

The Unified Reform Calendar shall be introduced on the first day of the first month of the year of the Unified Reform Calendar that starts after the year of the tenth anniversary of the enactment of this Act, with said anniversary to be calculated in terms of the Old System. That day shall be known as Calendar Switch Day. Unified Reform Time and the Unified Reform Longitude System shall be introduced on the fourth day of the first month of the year that starts on Calendar Switch Day, at 30 minutes past Midnight local time of the Meridian Astronomical Reference Point in terms of the Old System. That point in time shall be known as the Time Switch Moment.

Calendar designer's remark: The ten year delay was included to allow time for all the immense technical and administrative preparatory work needed for a change like this. I'm open to changing it to even more years, if people who know about this kind of thing should tell me that would be better. The Time Switch Moment was set at a few days after Calendar Switch Day so that it wouldn't interfere with Midnight on New Year.

Section 4

From Calendar Switch Day onwards, the Unified Reform Calendar shall be used for referring to dates in all official publications and records of the Institutions of the United Earth, including for referring to events and dates before Calendar Switch Day and before the Enactment of this Act; and the Institutions of the United Earth shall encourage the use of the Unified Reform Calendar. But outside of the production of official publications and records of the Institutions of the United Earth, no one shall be in any way forced against their will to use the Unified Reform Calendar.

Section 5

Nothing in this Act shall be interpreted as in any way changing or affecting the traditional seven day week or its observance.

Title 2 - Meridians, days, and timezones

Section 1

There shall be a Meridian Astronomical Reference Point, which shall be used to determine the Zero Meridian on Earth under the Uniform Reformed Longitude System. Other meridians shall be determined relative to it, while the traditional number of 360 geographical meridians shall be kept. Hours and minutes of the day shall be determined, so far as this is practically possible, in reference to astronomical midnight at the Meridian Astronomical Reference Point.

Section 2

The Meridian Astronomical Reference Point shall be a specific point in the place where, at the extent of sea level rise that has happened on the day of the enactment of this Act, the Equator intersects with the western coast of the mainland of the African Continent.

Calendar designer's remark: This is the concession made to Africans at the negotiations about the calendar. Of course they never admitted it officially, but unofficially, the negotiators were looking for a meridian that, in global terms, would not be that far away from the Greenwich Meridian, but could still be defined without referencing anything Western. Having some reference to something related to Africa in the new system was fairly important to some of the negotiators from African countries. Besides, this particular Zero Meridian meant that the new 180 degrees Meridian would still be a line roughly through the middle of the Pacific Ocean, which was seen as practically useful. The point in question is in Gabon, perhaps not exactly where the coast is now, and not that far away from the capital, Libreville, though of course it's possible that they'll have changed the name of the city by then. The meridian in question is about two thirds of the way between the Greenwich Meridian and the defining meridian of our time's West African and Central European timezone, so at the Time Switch Moment, the minute of the hour changed by about 20 minutes, while the new UTC was about 40 minutes different from the old UTC.

Section 3

After the Time Switch Moment, initially, the boundary lines between different timezones shall remain where they were under the old system, with only the time in the timezones themselves changing. But each local or regional jurisdiction shall have the authority, in accordance with the constitution and the laws of the Constituent State to which it belongs, to move to a different timezone.

Section 4

After the Time Switch Moment, the International Date Line shall initially remain where it was when this Act was enacted, and jurisdictions consisting of islands in the Pacific Ocean shall retain their traditional authority to decide for themselves on which side of the International Date Line they wish to be.

Section 5

Hours and minutes of the day shall, under Unified Reform Time, be determined in relation to astronomical midnight at the Meridian Astronomical Reference Point, but the beginnings and ends of seconds shall continue to be determined under the Old System.

Calendar designer's remark: For most of the negotiators, changing things by split seconds would have gone too far.

Section 6

The Minister of the United Earth whose area of responsibility includes astronomical scientific research shall have the authority to decree leap seconds in order to keep legal and astronomical time close to each other, provided that any such leap second must be announced at least five years in advance.

Calendar designer's remark: Leap seconds are already a thing in real life in our time.

Title 3 - The Calendar and the counting of years

Section 1

There shall be a Calendar Astronomical Reference Point, which shall be used to determine the astronomical aspects of the Unified Reform Calendar. References to Midwinter, Midsummer, solar equinoxes, and New Moon Days shall be interpreted as references to astronomical Midwinter, Midsummer, solar equinoxes, and New Moon Days at the Calendar Astronomical Reference Point.

Calendar designer's remark: For the reason why the Calendar Astronomical Reference Point is different from the Meridian Astronomical Reference Point, see the remark on the next Section.

Section 2

The Calendar Astronomical Reference Point shall be a specific point in the inner city of the city of Xi'an, Shaanxi Province, China.

Calendar designer's remark: This is the concession made to Chinese people at the negotiations about the calendar. Some suggested having only one reference point, the Meridian Astronomical Reference Point, but Chinese negotiators insisted on having something related to China in the new system. However, those negotiators from other countries who were resentful of Chinese influence insisted that the point in question would not be in Beijing, because they would have seen that as too on the nose. So they eventually settled on a city that had a certain historical significance in Chinese culture but was not the modern capital.

Section 3

Each year under the Unified Reform Calendar shall, subject to the restrictions of Section 5 of this Title, begin on the day that comes eleven days after the day of astronomical Midwinter at the Calendar Astronomical Reference Point.

Calendar designer's remark: This is the concession made to Westerners and non-Orthodox Christians at the negotiations about the calendar. It means that New Year under the Unified Reform Calendar would usually be either on or fairly close to the Gregorian January 1st.

Section 4

Each year under the Unified Reform Calendar shall consist of thirteen months, of which the first ones shall be of approximately equal length, and the thirteenth one shall be shorter. Each months shall begin on a day that shall be as many days after the most recent New Moon Day at the Calendar Astronomical Reference Point as the first day of the year to which it belongs was after the most recent New Moon Day at the Calendar Astronomical Reference Point.

Calendar designer's remark: This is in a way a concession made generally to people from cultures which placed a high importance on the Moon or used lunar or lunisolar calendars.

Section 5

As soon as possible after this Act is enacted, Parliament shall commission astronomical studies which shall determine the most likely dates of the astronomical events referred to in Sections 3 and 4 of this Title for 10,000 years in advance, and these calculated dates shall generally be used for determining the lengths of years and months during that time period. Later, such calculations shall, if possible, be made at least 8,000 years in advance. However, if new or unexpected developments in astronomical research or observations should prove these calculated dates to be invalid or false, the Minister of the United Earth whose area of responsibility includes astronomical scientific research shall have the authority to decree changes in the exact dates of years and months according to astronomical knowledge. Such changes shall, if possible, be announced at least 50 years in advance.

Section 6

The months of the year under the Unified Reform Calendar shall initially only be numbered and not have names. 40 years after Calendar Switch Day, Parliament shall establish a Commission, to be known as the Month Naming Commission, which shall investigate to which extent appropriate and non-offensive terms might have become commonly used as informal names of months in the everyday use of language. This Commission shall also have the authority, if it chooses to do so, to ask the general public for suggestions for names of months. Once this Commission has completed its work and delivered its final report, Parliament may amend this Act to introduce names of the months.

Calendar designer's remark: I kind of like the idea of something lke this being allowed to gradually grow from below instead of being decreed from above.

Section 7

For the counting of years under the Unified Reform Calendar, the Year Zero of that Calendar shall be determined in such a way that the Year 12,001 of that Calendar shall be the year of the event which the Islamic Religion calls the Hijra.

Calendar designer's remark: This is the concession made to Muslims at the negotiations about the calendar. Muslim negotiators insisted that there had to be some kind of Islamic element in the calendar. But using anything too close to the actual Islamic Calendar would have been a non-starter, for political, cultural, and as far as the length of the year was concerned, practical reasons. The 12,000 year distance was partly influenced by the old Holocene Calendar proposal and gave all known written historical events positive year numbers. And the year of the Hijra was designated as Year 12,001 instead of 12,000 as a concession to Iranian negotiators, to make conversions between years in the Unified Reform Calendar and years in the Iranian Civil Calendar relatively simple instead of a bit more complicated.

This is an interesting system and quite unique, I think I came across something similar elsewhere but it wasn't elaborated nearly as much as here.

I hope you don't mind some nitpicking (having seen the two limits of legal definitions of a calendar: the traditional Chinese calendar, the official standard for which was released in 2017 and rigorously defines every term used based on IERS definitions, and the Iranian calendar, which defines the new year only as "the first day of spring" and has since been disputed in interpretation).

In general I see several terms not properly defined. I'm not that familiar with where legal acts put such definitions, but I'd still like to see them.

More specific comments below:

• 1.2: I see no reason to avoid naming the Gregorian calendar here. (Incidentally, Inter gravissimas proper doesn't actually specify that much of the calendar, only the omission of 10 days and the skipped century years; most of it is in accompanying documents and quite a bit is implicitly the same as the old system.) Might be good to mention year numbering as well.
• 1.3: Define local time here; is this local civil time or something else?
• 2.1: Astronomical midnight isn't defined. I would assume you're referring to mean solar time, but it may also be interpreted as either apparent solar time, which is a non-trivial difference.
• 2.3: If the intent here is that UTC (or its equivalent at the time) will be substituted by the time reference of the Unified Reform Time system, this should be made explicit. Additional note: I would expect that before the Time Switch Moment many jurisdictions would define new timezones to take effect at the same time as the Unified Reform Time system, since an advance of 37 minutes 24 seconds is quite significant.
• 2.5: Possible ambiguity here. IMO this is the most awkward part of the text; if I were writing this I would instead describe a method involving an offset which is to be applied at the Time Switch Moment.
• 3.3: Astronomical midwinter not defined (this is not quite as ambiguous as some of the other terms, but still should be made clear); also it should be specified what kind of day is referred to here, and in particular whether this refers to civil time or solar time, and if solar time whether mean or apparent solar time (c.f. remarks on 1.3 and 2.1).
• 3.4: New Moon Day not defined. It's not clear what happens if a New Moon Day falls on the first day of the year.
• 3.5: Given the provisions of section 1.4 one might want to also compute the calendar for a few thousand years in the past. I note also that the reliability of the calendar calculations for the distant future (and distant past, for that matter) depends largely on how well understood are the mechanisms underpinning changes in Earth's rotation (and its effects on Delta-T).

Thank you! I admit that I'm not an astronomer or much of a calendar geek. And I thought my version was already too complicated - I wouldn't have thought that it would still be not complicated enough!