#mesoconvert

[ra-tutubixi]

The End of a Pain Begets Another: Musings on the Mesoamerican Calendar Translator, Maya Section

After some time, I found Prudence M. Rice's book (Maya Political Science: Time, Astronomy, and the Cosmos) contains a section entirely dedicated to the Short Count, by another name, the Waslason K'atun, or the "Cycle of the K'atun." Recall, if you will, that a K'atun is composed of 20 Tuno'ob, each 13 Winalo'ob, each 20 K'ino'ob/Days. Thus, a K'atun is approximately similar to 2 decades in the Gregorian calendar.

The table in Prudence's book helpfully exemplifies the "properties" of each K'atun name: if we begin counting in K'atun 13 Ajaw, the next will be 11 Ajaw, then 9 Ajaw, so on so forth until 1 Ajaw, at the end of which we continue with 12 Ajaw, then 10 Ajaw, 8 Ajaw, thusly until 2 Ajaw, which will be succeeded by 13 Ajaw once more. Such a cycle of 13 K'atuno'ob (the plural form of K'atun) is called a May.

The table, however, is also weird in its datings.

The story of Mayapan is set to the tune of prophecy and divine influence, set in their respective K'atuno'ob, with even some trademark cyclicality to the historical beats; the specific dates are provided by the Books of Chilam Balam, colonial-period recollections of the traditional knowledge of certain cities. Were we to count back from, say, K'atun 8 Ajaw (1185-1204; in LC notation, 1.10.18) when the Tutul Xiu overthrow the ruling Itzá dynasty, we'd find that K'atun 1.9.14 is a 4 Ajaw — but Rice (or, rather, Robert Sharer) posits it is one before, 6 Ajaw; conversely, 1.9.1 is posited as 6 Ajaw, but counting back instead gives us 4 Ajaw, again showing an offset of 1. This is a rather minor thing and may instead be intended to show the date in which a given K'atun ends, similarly to how gregorian decades are formally defined: the 2010s began in 2011, and their last year was 2020, while the two-hundredth-second decade began in 2021, etc etc.

So. We have a correlation!.. Kind of.

Traditionally, K'atuns are defined as being named according to their last day, some k'in ending in Ajaw, with a given number. You may try the MCT from a few posts ago, and you may find that such a correlation... does not exist. And I haven't yet quite the idea why. There is, however, the quirk that the nearest Ajaw date to the onset of a new K'atun miiight be the namer? Really depends on which K'atun you choose.

Because of the offset's seeming, uh, progressively accumulating offset, there is very likely something at play with the way leap years are accounted for. See, the other Mesoamerican calendaric systems we have implemented require, primordially, agricultural syncing, but also cross-round syncing. This is because of a little thing called the New Fire ceremony, which occurred every 52 years as the short round re-incided on the same days of the long round it had that many years earlier (for the Etetl, this may have been on a 1-Tekpatl, som specific day in the month of Panketsalistli, 2-Akatl year; still have to confirm this). So, because of the agricultural angle, there needed to be leap days (and, weirdly enough, we can trace one such "extra" day in Cortez' records of when he landed and when the Siege ended, and see a graphic representation of it in a codex), and the festive angle requires the short round "ignore" these extra days, for an offset between the rounds would begin to rear its head if it didn't.

But the Maya may not have had such a ceremony. Now, their long round is hypothesised to be also agricultural, and due to astronomical funnies it is likely their LR years also had a leap. Additionally, the Long Count does seem to have accounted for leaps, as dates basically line up perfectly between the Western calendars and Long Count, provided we convert from Julian to Proleptic Gregorian if needs be. So. We're left with the possibility that this specific short round did not need to correlate with the long round, but instead with the Long Count, and therefore with the derived Short Count.

I have yet to make tests to this hypothesis, but the lack of mentions of any convergence-specific importance between SR and LR may vaguely give support to it.

Also, bug report: the transition from the 28th to the 29th of January in the Maya LR is broken (there seems to be a theme here); instead of moving correctly in the month of Mol (12 to 13 or 13 to 14, depends if it's a leap year), it jumps directly to next year's Pop; this offset is "corrected" when reaching the transition from March to April, which correctly reflects as the actual year's 16 Sak'. I don't know why yet. This whole thing will be a hotfix + patch tba soon, but for now the Maya LR convertor will remain broken. Whoops.

Shouldn't take much time to fix it, just an adjustment to the Delta-values. Probably. But it's work and I can't do much of that rn. Nor for any particular reason, my vibe hasn't circled back to coding yet. I did add a thing to it to save your last converted date, or today if there wasn't any. Yay.

Bibliography:

Maya Politico-Religious Calendrics, in Prudence M. Rice (2004): "Maya Political Science: Time, Astronomy, and the Cosmos".

— (1999): Rethinking Classic lowland Maya pottery censers

Religious Institutions and Elite Power at Postclassic Maya Communities, in Marilyn A. Masson (2015): "In the Realm of Nachan Kan: Postclassic Maya Archaeology at Laguna De On, Belize"

Eleanor Harrison-Buck (2014): Reevaluating Chronology and Historical Content in the Maya Books of Chilam Balam

Harmeet Kaur (2019-12-28): When does the decade begin and end anyway?

Erik Boot: Fray Diego de Landa y la Cosmovisión Maya-Yucateca a inicios del Período Colonial, in Horacio Cabezas Carcache (ed., 2011): "Cosmovisión Mesoamericana".

+ relevant others from previous calendar post. consider this a continuation of it.

[ra-tutubixi]

The Wheel Ever-turning: A new system for Mesoamerican date conversions

Mesoamerican timekeeping has for a long time been a subject of ardent discourse between different strains of academia. Time and time again, a new correlation comes along from newer and finer studies on what few attested dates we have for certain, and we build on top of past ideas. Today, I present to you not just a correlation, but an interactive tool to satisfy all (or at least some of) your meso time needs.

Link to the tool: https://cornlands.neocities.org/tools/mesoconv

The Long Count, and other design choices

There must always exist constraints for any and all projects. For us, this manifests as selecting bases and pathways to get from point A to point B in whatever way it seems most efficient.

I first came into acquaintance with the Long Count as correlated by Thompson, who in turn built on top of Martínez and Goodman. Collectively known as GMT, their work offers a great deal of joy to any world-builder and aficionado alike. Their correlation, however, is most often stated as pegged to the Proleptic Gregorian Calendar, an extension of the widely-spread system that manages dates predating its introduction.

The Long Count offers an interestingly early epoch of April 1st, -8239. It is an incredibly elegant system that allows one to pinpoint the exact number of days between two events, regardless of hurdles such as irregular earth days and tidal slowing. There is a slight problem, though.

I began this project perhaps one or two years ago, with a rudimentary Gregorian-Long Count convertor. I was quite less versed in calendarics, let alone coding, although I managed to conduct myself well-enough to produce such a tool. The script used for that project first translated the Gregorian year into a Holocene year, mostly for ease of counting and leap-accounting, and summed an aggregate of days for the corresponding month — which had been calculated by hand — and then multiplied the delta of time between the epoch and the year preceding the input times 365. The leaps were then counted with the Gregorian conditions, (d % 4 == 0 && d % 100 != 0) || d % 400 == 0, but it checked Every Single Year with a while loop. Inefficient as all hell, but effective. Finally, input days were subtracted by 1 and added to the count.

Last week, I returned to the project with a little more knowledge and more pencil and paper to calculate whatever would be needed. I managed to slash the code by a third through making a few things more algorithmic: the number of leaps was first calculated in the julian way (d % 4 == 0), then fine-tuned with the second and third gregorian conditions, subtracting the matches for the former and re-adding those that fit the latter. The formula now stood as (((x - (x % 4)) / 4) + ((x - (x % 400)) / 400) - ((x - (x % 100)) / 100)), though since this counts all leap years since Holocene epoch, one needs to subtract the number of leaps from HEpoch through LCEpoch, 427.

Months were another reduction, as two methods were now used. If the month is lesser than April, each will get the corresponding aggregate day reduction, plus the leap day if applicable to the year and month (February and January). For months after April, I got lazy and merely added a while loop which would check if the month preceding the input was a 31 or 30-day one. April itself is not checked, since only month days need be added in its case.

These both produce a single integer, the days between LCEpoch and the input. This is to become the base for the rest of my calendar tools.

Finally, both versions implement another while loop and what amounts to a switch, which will check if a piktun, b'ak'tun, k'atun, tun or winal can be removed from said integer, and will increment the corresponding position by one. Remaining k'ins are merely added to their counter if applicable.

The LC is not quite as homogenous as one would think, though, and has an irregularity past the first 13th b'ak'tun: it immediately jumps to piktun 1, b'ak'tun 1, instead of resetting itself to b'ak'tun 0. This was also accounted for with a conditional before the loop that will similarly raise the b'ak'tun to 1 if it detects that there is a piktun completed. I infer that the next piktun will begin similarly as the current one did, with a b'ak'tun 1 instead of 0.

The Short Round, i.e. the Count of Days

I decided to hard-code an epoch corresponding to the Long Count, to merely use more sums and modulos to quickly calculate day numbers and signs. This, little did I know, initiated a cascade of issues.

Firstly, the matter of the epoch. Though we have the date 8 koatl as a peg to Nov. 8, 1519, this second date is written in the Julian calendar. For compatibility, this date was translated into a Gregorian one (Nov. 18). The count from LCEpoch through Nov. 18, 1519 (sans leaps for a reason explained below), was obtained with a modified version of the initial LC function, and through the use of modulo 13 and 20 I obtained, respectively, the day number and sign corresponding to it, by receding one sign per unit overshooting each operator. The finalized date comes out as 4 death.

The tool will first multiply the delta of years from LCEpoch by 365, then proceed with the addition/subtraction of the months, and finally the addition of remaining days (again, without leaps). It will then calculate its modulos 13 and 20 and fetch the correct sign.

Both the (Central) Nawa & Yühü SRs seem to have the same epoch, though they do have a slight discrepancy on leap years, as the end of the Dupa and the Nemontemi aren't quite the same. This distance opens at one at the end of the former, and closes itself back up at the end of the latter.

The Classic Maya SR has a specific discrepancy of 217 days relative to the Central-International SR. This was obtained from the 13.0.0.0.0 epoch (Aug. 11, -3114), said to be 4 Ajaw 8 Kumk'u. LCEpoch in terms of the Maya SR would be 12 Akb'al.

The Zaa SR is named Biye, and is offset by 94 days from the C-I SR. The LCEpoch would be Bilainaa (7-Milpa) in this Round.

The Long Round, i.e. the Count of Years

Most freely-available convertors (and calendaric descriptions) posit that Mesoamericans did not have leap days, and that the Long Round fell prey, slowly and inexorably, to the inverse phenomenon of that which befell the Julian calendar.

A simple observation, common across all regions, would disprove such a notion: the calendar followed the seasons. It is more than naïve to suppose that a whole civilization, spanning several millennia and with a noted knack for observing the skies and patterns on the earth, would not have noticed their months, themed around such phenomena, slipping away from them.

Though the position of a leap day (or moon, as some have argued wrongly) has been the subject of much discussion, Ochoa's work has led us to trace it to the tail-end of the Dead Days, those finalizing each year, and particularly as falling on every Flint year. Given that both rounds need to match up every 52 years, and that the two most secure dates (those being, the arrival of Cortez and the fall of Tenochtitlan) seemingly "skipped over" a day in both the Short and Long round, we have assumed that these "Deader Days" were skipped by the former, and the tool will simply display an N/A on such occasions, returning to a regularized count at the beginning of the year.

The epoch year was, again, calculated with modulos 13 and 20, which resulted in the pair 7 Rabbit. The moon and day were simply counted back from the one secure date we have (2 Quecholli - Nov. 19), resulting in the 11th day of the 2nd moon (Tlakaxipewalistli).

Cyclicality is a well-known quality of the Mesoamerican calendar. There is, however, a system sort of akin to the Long Count of the Maya and Isthmian areas too: the Eninanwixui. Translatable as "the Nightfall Count," one Anwixui corresponds with a cycle of 52 years, and 100 of these cycles correspond to a unit in the Thebe, the "hundred-collar." The length of the smaller cycle corresponds to the smallest of the periods used to calculate eclipses, using a 52-54-56-year-succession rule: while in the years befalling the middle rule an equivalent eclipse will occur, those under the first and third rules will vary.

We have two anchors for the cycle, these being the years 1456 and 1508. Assuming that its epoch and that of the Long Count aren't too far apart, -8239 would be within 0T.0a (0 Thebe, 0 anwixui), being the 22nd year within such first T.A-Cycle. Its epoch would therefore be -8261. This appears to be unique to the Yühü calendar, though the Hem'i Antämatsits'i perhaps hints at a possible Nawatl name for three such Anwixui, "kōāpantli." Given that this last hypothesis relies on a bit of interpretative reading (moreso than the average codex experience), the tool will not implement this latter name.

Coding this section took very many reworkings, though I am proud to announce it successful. The tool will begin its count on the epoch year per the Holocene calendar (to more easily account for leap years), and cycle through the raw day number input: first it will check if years can be added to its count, then months, then days. The function will account for leap days when skipping over the Dead Days. I'm sure you could do something formulaic with the Anwixui and stuff, but I decided it was a tad too complex to develop an algorithm for the scope of this project. If I shall ever implement reverse-conversions, that will probably be somewhere at top priority.

The Yühü LR has two names, as it is recognized to have two separate (albeit interdependent) parts: the Eninabenje̠ya is the count of years proper, while the Eninabeningo is the month+day count; the latter one was called Eninabenzänä in Mamëni (Tollan-Xikokotitlan). The LCEpoch is the same year, albeit such begins 18 days earlier than in the Nawa LR (making the LCEpoch date 20 Ants'ä'yo).

The Maya LR has an offset of 185 days relative to the Central-International LR. Again, this is from the epoch; the initial day here would come out as Year 6 Lamat, Sak' moon, day 16.

The Zaa LR is known as the Iza. It has an epoch slightly earlier than the Nawa-Yühü calendar, about 7 or 8 days. LCEpoch corresponds to Year Yoochina (5-Deer), Wistao moon, day 8. This calendar is particularly notable for holding two "short moons" instead of only one: the Kichola resemble the Dead Days the most, but after it comes a remarkably short period, only two days long (or three on leap years) called the Keainij. I cannot hope tho provide a gloss of either term, nor their connotations, only noting that because of precedent, it's highly likely that the Biye stopped whenever there existed a third Keainij day.

Potential future expansions

Though already quite complex and, dare I say, interregional, it is still very much in its infancy. A list of things I's like to add follows, and suggestions are always welcome, as well as contributions.

Trecenas and ruling deities

Lords of Night

Lunar and 819-derived Series

Short Count

Julian-Gregorian equivalencies, if for practicality

Numbers in the International Style, not the Unicode imitation I forced in

A Glyph aside the current Moon and Year-Sign, and Short Count. Maybe above/below LC too.

MORE LANGUAGES!! (+Teoti glyphs?)

LC-to-everything conversions, directly

Alternate names (regional variances and otherwise by-names)

Day, period, year and moon semic charges

Comments and such

The calendars don't match up perfectly, as we have repeatedly mentioned. The Maya Short Round can be said to be 217 days ahead of the Yühü-Nawa one, while the Long Round is instead 185. This should perhaps be of little surprise, given how fluid culture and conventions tend to be in the region, but it is nevertheless remarkable, whatwith the well-integrated trade networks and just the immediate resemblances of both calendaric sets when compared side-to-side. Such situation may be an echo from times long past yet present, as the Maya area is historically more of its own "bubble" in terms of culture, with varying degrees of synchronicity. Indeed, the Gulf Lowlands and the Chiapanec Corridor were its stronger nexus to the rest of Mesoamerica for long, and what should we find in these regions but "habitones," peoples and regions whose habitus could be placed in a gradient of relatedness to both sides of the Isthmus.

Such discrepancies occur even within what could be called Central Mesoamerica, the birthplace of an on-the-nose-nym'd International Style.

I tried to add the Short Count but failed, becoming prey of much despair in the process, in part because its existence is noted but seldom explained in full, and in part because quite often it is used for discourse and academic invalidation of surviving traditions.

I also tried to add the Mixtec Rounds, but couldn't quite find much info on the LR. I'm not about to half-ass smth, but ig if it gets enough requests (if any lol) I'll try n make a draft version of only the SR in the same style as the draft LC thingy.

I had to do some last-minute extra debugging bc, of course, I forgot that our year and the Nawa year begin at slightly different times. Somehow I didn't think to check the MANY notes I had on the topic, but reading an old post of mine elsewhere made me remember. It's all done now, and the code is slightly improved so that things don't break on some odd days.

Bibliography

Thomas Chanier (2015): The Mayan Long Count Calendar

The Aztecs did not need a leap year: Introducing the Nuttall-Ochoa model for the Aztec Calendar (2017-04-26), published in "Nawatl Scholar."

Anales de Cuauhtitlan

David Charles Wright-Carr (2005): Los otomíes: cultura, lengua y escritura, Volumes First and Second. – Hem'i Antämatsits'i (Análisis y transcripción de D.C. Wright-Carr)

Codex en Croix [sic.], copie dans la Bibliothèque Nationale de France (avec le nom "Album. Cruz", n.class. "Mexicain 90(2)").

Geraldine Patrick-Encina (2011): El calendario hñahñu: un análisis epistémico y semántico para establecer su estructura

Rossana Quiroz Ennis (2016): Eclipse Count, Calculation or Prediction According to the Huichapan Codex

J. Eric Thompson (1935): Maya Chronology: the correlation question

Howard F. Cline and Mary W. Cline (1975): Ancient and Colonial Zapotec and Mixtec Calendars: A Revisionist View

Maestros de la Región Ya'a/I'ya, Florentino Ambrosio, Ricardo Ambrosio, Eleazar Bautista, Marta Cruz, Gaudencio Fentánez y Manuel Ríos (2019): Bene’ wesedl, bene’ ya’a – maestros de la sierra: lectura intercultural de los días zapotecos en el corpus de Lachewize

José Alcina Franch (1996): Calendarios zapotecos prehispánicos según documentos de los siglos XVI y XVII

[ra-tutubixi]

Update/pachnote 1.1: The bug with the Maya calendar has been fixed.

Update/patchnote 1.2: The Maya Short Round does, indeed, run on leap days; the corresponding update to the code and re-alignment of the deltas has been made. While the Maya did have a New Fire ceremony, this was every 63 k'in (Guillermo Bernal Romero, 2016: El ciclo de 63 días en la cultura maya: descubrimiento de un nuevo factor calendárico), not at any correspondence of calendars. Additional note: the K'atun were therefore, indeed, counted like decades: 1.11.19 begins at 1.11.19.0.0.1 and has its last day in 1.11.20.0.0.0.

Update/patchnote 2.1: The Short Count has been added successfully. Its epoch is the last (and thus eponymous) k'in within K'atun 4 Ajaw. The formula came out as ((-2 * numberOfPastK'atuns) + 2) % 13, with a special case adding 13 to the output if such is lower than 1, in such a way that it effectively loops back around before the modulo hits floor 0.

Non-patch-devnote 3.1: There seems to be a fascinating bug with moving between entire years while in the Wayeb' period, as it appears this part of the calendar will persist with 5 days even if the new year is a leap. this problem appears not to happen when the day-to-day arrows are used, and is only apparent with the "big jump." Not sure about the "small" month jump.

Non-patch-devnote 3.2: Somewhere, the thing that turns the number wheel on the Maya Sacred Round visual rep. broke. Have a vague idea what and where, but as it is a minor thing and the rest works well I might leave it as-is for a while, until it bugs me enough.

Comment 4: There are also two other components of the Short Count, the Waslason Tuno'ob and Waslason Winalo'ob (Daniel Graña-Behrens, 2017: La Cuenta de los K’atuno’ob: rituales y regionalismos en el período Clásico maya), though not nearly as seemingly prominent. Their "hops" are of 4 and 6 coefficients respectively, and form a neat triad with the main Waslason K'atuno'ob (which might indicate that they are derived from it?).

The End of a Pain Begets Another: Musings on the Mesoamerican Calendar Translator, Maya Section

After some time, I found Prudence M. Rice's book (Maya Political Science: Time, Astronomy, and the Cosmos) contains a section entirely dedicated to the Short Count, by another name, the Waslason K'atun, or the "Cycle of the K'atun." Recall, if you will, that a K'atun is composed of 20 Tuno'ob, each 13 Winalo'ob, each 20 K'ino'ob/Days. Thus, a K'atun is approximately similar to 2 decades in the Gregorian calendar.

The table in Prudence's book helpfully exemplifies the "properties" of each K'atun name: if we begin counting in K'atun 13 Ajaw, the next will be 11 Ajaw, then 9 Ajaw, so on so forth until 1 Ajaw, at the end of which we continue with 12 Ajaw, then 10 Ajaw, 8 Ajaw, thusly until 2 Ajaw, which will be succeeded by 13 Ajaw once more. Such a cycle of 13 K'atuno'ob (the plural form of K'atun) is called a May.

The table, however, is also wrong in its datings.

The story of Mayapan is set to the tune of prophecy and divine influence, set in their respective K'atuno'ob, with even some trademark cyclicality to the historical beats; the specific dates are provided by the Books of Chilam Balam, colonial-period recollections of the traditional knowledge of certain cities. Were we to count back from, say, K'atun 8 Ajaw (1185-1204; in LC notation, 1.10.18) when the Tutul Xiu overthrow the ruling Itzá dynasty, we'd find that K'atun 1.9.14 is a 4 Ajaw — but Rice (or, rather, Robert Sharer) posits it is one before, 6 Ajaw; conversely, 1.9.1 is posited as 6 Ajaw, but counting back instead gives us 4 Ajaw, again showing an offset of 1. This is a rather minor thing and may instead be intended to show the date in which a given K'atun ends, similarly to how gregorian decades are formally defined: the 2010s began in 2011, and their last year was 2020, while the two-hundredth-second decade began in 2021, etc etc.

So. We have a correlation!.. Kind of.

Traditionally, K'atuns are defined as being named according to their last day, some k'in ending in Ajaw, with a given number. You may try the MCT from a few posts ago, and you may find that such a correlation... does not exist. And I haven't yet quite the idea why. There is, however, the quirk that the nearest Ajaw date to the onset of a new K'atun miiight be the namer? Really depends on which K'atun you choose.

Because of the offset's seeming, uh, progressively accumulating offset, there is very likely something at play with the way leap years are accounted for. See, the other Mesoamerican calendaric systems we have implemented require, primordially, agricultural syncing, but also cross-round syncing. This is because of a little thing called the New Fire ceremony, which occurred every 52 years as the short round re-incided on the same days of the long round it had that many years earlier (for the Etetl, this may have been on a 1-Tekpatl, som specific day in the month of Panketsalistli, 2-Akatl year; still have to confirm this). So, because of the agricultural angle, there needed to be leap days (and, weirdly enough, we can trace one such "extra" day in Cortez' records of when he landed and when the Siege ended, and see a graphic representation of it in a codex), and the festive angle requires the short round "ignore" these extra days, for an offset between the rounds would begin to rear its head if it didn't.

But the Maya may not have had such a ceremony. Now, their long round is hypothesised to be also agricultural, and due to astronomical funnies it is likely their LR years also had a leap. Additionally, the Long Count does seem to have accounted for leaps, as dates basically line up perfectly between the Western calendars and Long Count, provided we convert from Julian to Proleptic Gregorian if needs be. So. We're left with the possibility that this specific short round did not need to correlate with the long round, but instead with the Long Count, and therefore with the derived Short Count.

I have yet to make tests to this hypothesis, but the lack of mentions of any convergence-specific importance between SR and LR may vaguely give support to it.

Also, bug report: the transition from the 28th to the 29th of January in the Maya LR is broken (there seems to be a theme here); instead of moving correctly in the month of Mol (12 to 13 or 13 to 14, depends if it's a leap year), it jumps directly to next year's Pop; this offset is "corrected" when reaching the transition from March to April, which correctly reflects as the actual year's 16 Sak'. I don't know why yet. This whole thing will be a hotfix + patch tba soon, but for now the Maya LR convertor will remain broken. Whoops.

Shouldn't take much time to fix it, just an adjustment to the Delta-values. Probably. But it's work and I can't do much of that rn. Nor for any particular reason, my vibe hasn't circled back to coding yet. I did add a thing to it to save your last converted date, or today if there wasn't any. Yay.

Bibliography:

Maya Politico-Religious Calendrics, in Prudence M. Rice (2004): "Maya Political Science: Time, Astronomy, and the Cosmos".

— (1999): Rethinking Classic lowland Maya pottery censers

Religious Institutions and Elite Power at Postclassic Maya Communities, in Marilyn A. Masson (2015): "In the Realm of Nachan Kan: Postclassic Maya Archaeology at Laguna De On, Belize"

Eleanor Harrison-Buck (2014): Reevaluating Chronology and Historical Content in the Maya Books of Chilam Balam

Harmeet Kaur (2019-12-28): When does the decade begin and end anyway?

Erik Boot: Fray Diego de Landa y la Cosmovisión Maya-Yucateca a inicios del Período Colonial, in Horacio Cabezas Carcache (ed., 2011): "Cosmovisión Mesoamericana".

+ relevant others from previous calendar post. consider this a continuation of it.