A
1
How this file works:
2
This file aims to take a Julian or Gregorian data as input and generate a view of the Mexica calendar(s) for the equivalent date in the Xiuhpōhualli and Tōnalpōhualli.
3
Labels for any reusable or cyclical things (day names and numers, month names and numbers, 52-year cycle of year names, etc) live in the Data tab.
4
The Aligner tab has centuries of equinox data for Mexico city, plus time zone info and calculations, year length calculations for Julian and then Gregorian calendars.
5
Then Aligner checks whether the vernal equinox would have been detected before 11:15am (solar time) on equinox day. If yes, that day ends the Xiuhpōhualli; if no, the next day does.
6
The Aligner sets the first day of the new Xiuhpōhualli, and maths out whether it will be a 365-day or 366-day year.
7
YearMaker tab pulls lables from Data and info from Aligner to actually process the Julian or Gregorian date and generate the given year's day names (365 or 366 days of both Xiuhpōhualli and Tōnalpōhualli day names).
8
(While the math that applies day names and numbers to all days of the year happens on YearMaker tab, it's actually copying the date entered in the orange cells of the Xiuhpōhualli tab)
9
Xframe provides the structure for pulling the first, second, third... 366th day names into a calendar visual.
10
Xiuhpōhualli then assembles day labels from YearMaker according to the structure of Xframe, and uses conditional formatting to highlight the chosen day and the month in which it lands.
11
Xiuhpōhualli2 does the same display, except veintanas are presented five to a row instead of four.
12
If you see something not working, type it in the ISSUES tab, please. I might even fix it.
13
14
For those unfamiliar with the Xiuhpōhualli and Tōnalpōhualli:
15
The Xiuhpōhualli is a solar calendar. This file attempts to use Rubén Ochoa's correlation of it with the Julian calendar - the day on which the vernal equinox is observed before 11:15am local solar time becomes the last day of the year.
16
The point of reference most cited for the equinox's observation is Tenochtitlán's Templo Mayor.
17
Before the Templo Mayor or Technochtitlán existed, this file pretends they did. But: the same approach taken at a diffferent latitude, longitude, altitude and viewing angle would result in a slightly different observation cutoff time.
18
The first day of the new Xiuhpōhualli is therefore the day after the vernal eclipse is observed or confirmed.
19
The Tōnalpōhualli is the 260-day ritual calendar (a length likely aligned with human gestation).
20
Both Xiuhpōhualli and Tōnalpōhualli use veintanas or metztli: counts of twenty days. The Tōnalpōhualli matches up 20 day symbols/names with 13 day numbers.
21
After 360 days, the Xiuhpōhualli eaches the end of its veintanas. The remaining days are outside any veintana, and called the Nemontemi.
22
In a normal Xiuhpōhualli, the equinox is observed on the 365th day of the year, and there are 5 Nemontemi days.
23
When the equinox is not observed before the 366th day, there are 6 Nemontemi days, and the ritual Tōnalpōhualli repeats the same day name and number on on 5 and 6 Nemontemi.
24
Local solar time means local time as if the sun were highest in the sky at noon. Mexico adopted standard time in the 1920s, requiring adjustments to find solar time.
25
26
27
For those unfamiliar with Julian versus Gregorian calendars:
28
The Julian calendar counted leap years every 4 years - a little too often to keep the seasons alighed with the dates. That's why it was replaced with Gregorian.
29
In Mexico, the Julian calendar stopped being used on Oct 4, 1582. Gregorian calendar started on October 15th, 1582. October 5-14 were skipped over.
30
The Gregorian calendar counts leap years every 4 years, except for 3/4 of years ending in 00. Years evenly divisible by 400 are still leap years.
31
Spreadsheets natively pretend the Gregorian calendar was always used (this is called "proleptic Gregorian"). Some computer scripts have the same problem. This spreadsheet bypasses that behaviour.
32
33
For those curious about the maker of this file:
34
I'm a Canadian gringo. I started making this sheet when I wanted to have more convincing dates in a story I'm writing, mostly set in Mexico in the 1300s. I had no idea at the start that this would become so complex.
35
Please assume errors are mine.
36
If you're interested in playing with how it works, you can make your own copy of this file - in your copy you would become able to edit all the things I've locked here.
37
For a proper conversation, you can reach me at: challengesterriers@gmail.com . Forgive slowness to reply.
38
39
Credits and thanks:
40
on Reddit, u/TUSF once posted this Mayan calendar spreadsheet, which started me off and which still shows in the Xiuhpohualli tabs' look: https://www.reddit.com/r/Mayan/comments/twlkar/maya_calendar_spreadsheet/
41
also on Reddit, u/ItztliEhecatl was immense help - with some answers provided in conversation, and others by looking at his YouTube and web content.
42
...his web content included this page, which set the reference dates used in this file to count forward and backward: https://www.calmecacanahuac.com/tlaahcicacaquiliztli/index.php?title=Calendar_Correlation&oldid=281
43
For vernal equinox days and times as observable from Mexico City, I relied on https://www.timeanddate.com/calendar/seasons.html?year=1550&n=155
44
I can't remember what source I went to (after starting with AI chatbot queries for generalities) to validate how many minutes solar noon is from observed noon since Mexico started using standard time.
45
I was inspired by https://sites.google.com/view/tonalamatlahtolcuepalli/ , and I forgive that, as a prototype, it has errors that require adjustment (see row 31). It offers rich info about days and months to make up for it.
46
This episode of "Tales from Aztlantis" started me off deciding the Ochoa correlation made the most sense to me: https://www.youtube.com/watch?v=_ruu-rhno7g .
47
Early this spring, I had the great fortune a telephone conversation with Ruben Ochoa. I'm thrilled that I didn't need to change anything after, and we both left the conversation with interesting questions.
48
49
Apologies:
50
I very rarely receive mail from users of this file. I realized that by checking my email today after serveral months of not doing so, Sorry I've been slow, but I do check - and reply.
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100