u/CodapopKSP

Greetings! I am working on a project to calculate and document all of the world's calendars from the past and present. It is called the Library of Time: https://libraryoftime.xyz/

There is a calendar used by the Igbo people, referred to as the Igbo calendar. I have calculated it on my site (you can find it under Solar Calendars, or look for Nigeria on the map). However, there are a few questions that I have before I am confident in its accuracy.

1. When does the day typically start? In the West, it is at midnight. In other cultures it is at other times, like sunrise or sunset. From my understanding, it might not be specifically defined in the Igbo calendar, but is there any cultural reason or feeling that it might be one way or the other?

2. The Wikipedia article mentions the following:

> The first month starts from the third week of February making it the Igbo new year. The Nri-Igbo calendar year corresponding to the Gregorian year of 2012 was initially slated to begin with the annual year-counting festival known as Igu Aro on 18 February (an Nkwọ day on the third week of February). The Igu Aro festival which was held in March marked the lunar year as the 1013th recorded year of the Nri calendar.[8]

From my understanding, the Igbo calendar is a solar calendar that counts 365 days, not a lunar calendar. To be a lunar calendar, it would have to roughly count either 355 or 385 days per year (lunar cycles are about 29.5 days each, 12 or 13 can fit in a solar year). Is there a lunar calendar system that is associated with the Igbo calendar? Also, that wikipedia article mentions the 1013th year of the Nri calendar, but I was unable to find any other source that mentions year counting. Is this something that is part of the Igbo calendar? Is there also a Nri calendar?

I have a request to the people here for help with a project that I've been working on to create a universal time calculator. It's called the Library of Time. https://libraryoftime.xyz/

My goal is for it to eventually rise to the level of academic source. In some cases I may have achieved that, and in others I still have more work to do. One of the issues I have is that my astronomy calculations have some drift. I've read and implemented the calculations from Jean Meeus's Astronomical Algorithms. I've found my output to have significant drift compared to this website that seems to know what it's doing, so I'm pretty sure I'm doing something wrong.

Unfortunately, these calculations are super long, but if you'd like to see them they are in the repo here. One of the requirements of the project is that everything is calculated in-house. So I need to write my own calcs and they need to be done on-device and offline, so I can't just grab lunar phase data from some API somewhere.

A few things that highlight my problems more clearly:

1. The new moon of January 1000 BC is shown on that site as Jan 11 10:13, which I assume to be astronomical dating. My calc outputs Jan 11 09:55 (actually Jan 1 in Gregorian, but it converts to Jan 11 in astronomical). All the phases around that time are about 20-30 minutes off. Is that a reasonable amount of error to expect from Meeus's calcs?

2. My Alcyone/Pleiades position or moon position seems to be way off. I used Astronomical Algorithms for the source. One of the calendars requires calculating the time that they are in conjunction, but when I check sites like Stellarum, my calculated time of conjunction is up to an hour (time minutes, not coordinates) off. So I first calculate when the right ascension matches the RA of Alcyone displayed on Wikipedia, and then I run that Stellarum model to that time and compare if it visually matches, and it never does. It's always close but clearly off. The moon often occludes Alcyone, which should be the time of RA match, but it's often 30-60 minutes off.

Can anyone please help me understand why this might be happening?

I have a request to the people here for help with a project that I've been working on to create a universal time calculator. It's called the Library of Time. https://libraryoftime.xyz/

My goal is for it to eventually rise to the level of academic source. In some cases I may have achieved that, and in others I still have more work to do.

Currently I am still compiling calendars but have begun to hit walls with a few historic calendars. Some of these might not be possible to calculate given the existing available literature while others might be possible with the help of someone who is from that culture or has deep knowledge of that culture. Help can be in the form of direct help, providing sources, or pointing me to someone who can do one of those.

A few specific things I need help with:

• Providing historic rules for calculating the Japanese lunisolar calendar pre-1844. Currently I am using the Chinese calendar and some hard-coded values from NOAJ, but the calendar changed several times throughout history and my calculated output is frequently a day or two off from the ephemeris. I suspect this may have to do with shifting definitions of mean solar/lunar movement.

• Providing historic rules for calculating the Chinese calendar pre-1645 for similar reasons.

• Providing language and history help regarding the Vietnamese and Korean calendars. I haven't been able to find proper sources for these, but I suspect it may be due to a language barrier. Currently these are also using the Chinese calendar, which provides accurate dates in modern times but are likely to suffer from similar issues as the Japanese and Chinese calendars. A bigger issue is that I have no clarity on what these calendars looked like in pre-modern times.

• Providing any information about African calendars (non Ethiopian or Egyptian). A lot of them, such as the Igbo, Akan, and Yoruba calendars, have almost enough information to calculate but are missing some key info, usually regarding intercalation. Information online for these calendars is sparse and filled with misconceptions.

• Providing information for Maori calendars or similar, for the same reasons above.

• Providing information on Roman and Aztec calendars. I suspect these aren't possible to calculate due to missing information, but someone with great familiarity with these cultures might be able to provide more clarity.

• Providing deeper understanding of the difference between Indian calendars. I've had a lot of trouble calculating these because there are several of them and their rules aren't often posted online or are missing some key info. I believe this should be relatively straightforward for someone who studies Indian culture since most Indian calendars are still in use.

• Astronomy help, especially improving my lunar phase and equinox calculations and improving my stellar coordinates calculations.

I'm also open to any other info or suggestions. If you know of a missing calendar, please reach out! Thank you.

EDIT: To clarify at a moderator's suggestion:

> *Please be open about why you’re asking and how the information will be used, including how any substantive help will be credited in the final product.

> Alternatively, especially if this is a commercial project, consider hiring a historical consultant rather than relying on free labour here. While our flaired users may be happy to engage in such work, please note that this would need to be worked out privately with them, and that the moderation team cannot act as a broker for this.

Regarding the above two points, this project is entirely in the public domain, including the code (free open-source) and all information within it. My only goal here is to compile information in a novel way and share it with the world for educational purposes. Significant help would indeed be noted/cited, though by necessity it would also become public domain.

> *While our users are often happy to help get you started, asking someone else to do foundational research work for your project is often a big ask. If this information is absolutely vital for your work, consider asking for reading suggestions or other help in doing your own research.

I would be thrilled to be pointed in the right direction for any of my questions. I am only coming here after my own attempts at research have fallen short or if I feel the available online information isn't reliable.