Festival calendar tool


I’ve been making a calendar tool, based on the suggestions from the How & when are you celebrating Wep Ronpet 2023? thread.

You can use the latest version of it here.

If you save it locally it can be used offline as well.

So far it lets you select the date for Wep Ronpet using a date picker, and defaults to 7th August, choosing the year so that you can see today’s date. If you press apply to change the date it will append a query string so that you can copy-paste the link.

Clicking on the days shows some information in a sidebar or at the bottom depending on the screen proportions.

The festival dates are from this webpage from UCL.

I’m going to continue working on it to improve the quality and the available features, but if anyone has any suggestions or complaints, please let me know.

There is a github project here if you want to contribute directly.


Amazing!!! Good job :+1:t4:



After seeing it on some phones, I’m going to try to improve the layout on small screens - maybe have a single column display for those cases so that the dates are nice and large and easily touchable.

Beyond that I’d like to spend some time trying to work out how to add some nice options… display options for the month names, days, and detail on the sidebar - as well as options for different festival lists.

Once that is in a state where I feel it is highly useable, I’ll start thinking about a suitable model for working out the heliacal risings

I’m also thinking it would be nice to be able to have a selection between multiple sets of festivals, and checkboxes for them. I’ll start with the existing Festival Calendar we have here, and the Kemetic Reform calendar, maybe organising the UCL ones into subsets… and eventually having the option to include or exclude specific festivals from each list.

Update: some of this is now done, and its possible to share dates with links, like this:


The months can be displayed using the Middle Kingdom, New Kingdom or Greek names from Wikipedia (transliterated).

I’m going to skip the calendar from the forums since its hard to work out where Wep Ronpet should sit within it, given that it is keyed off of Gregorian dates… but I will add the Kemetic Reform dates as an option.

Update 2: There is now location selection, although it will only tell you if you choose a latitude where the Sirius never rises at all. I’ve added Greenwich Observatory and the Great Pyramid as presets, as well as your current position if you give permission.

I’ve written enough code to evaluate a pretty good approximation to the position of Sirius, good enough to work out the heliacal rising, but I will leave that part for my next opportunity to work on this…

Update 3: I’m slowly working through the astrometry code required to calculate the sunrise/sunset, I will finish these on the way to computing the heliacal rising dates. Its probably going to be a little while before I can post another meaningful update in that direction…

If anyone is using this or has any feature requests, let me know and I’ll do those as a priority.

Update 4: Sun and Sopdet sky positions are now calculated to within a degree…

Update 5: Now with timezones and accurate altitudes for Ra and Sopdet.

Update 6: Now with sunrise/sunset accurate to within a minute or two… and a quick pass on a dark theme.

Update 7: Now marks the predicted heliacal rising date correctly, based on an arcus visionis of 10 degrees.


I’ve started adding the Kemetic Reform festival dates, but there seems to be an error in their calendar having 31 days for the first month that I’m not sure how to resolve…

(use the calendar like this to see what i mean… )

EDIT: never mind… worked it out. just one mistake that is easily worked around.

EDIT 2: this now all works quite nicely, although the leap day does make it odd

1 Like

How odd! I wonder what the reason is for that leap day…

I’d assume its to keep in line with the Gregorian calendar…

I think I will add a drop down for the option to have leap days occur in line with the Gregorian calendar, as is done here, or at the end of the intercalary days as with the Coptic calendar, or not at all. This way the other festival calendars which are not tied to specific Gregorian dates can use the same methods if chosen by the user.

Next up though I’m going to try and work out how to continue the calendar from the one used in Claudius Ptolemy’s time rather than choosing a Wep Ronpet date.

There is an interesting implementation here: Date Converter for Ancient Egypt

Another one here: Online calculator: Ancient Egyptian Calendar.

I can use these to test, although I will be curious to see what I can come up with. The work should also serve as a good foundation to build a longer king list and a chronology.

1 Like

I can see that this project is growing arms and legs!

1 Like

Its a surprisingly frustrating task to create a robust solution here… I want to say Ptah has set me up here, but really it is just that this task is quite daunting.

Or I want to blame my ancestors…

Someone certainly screwed up our calendars, and it wasn’t me! :stuck_out_tongue: . Trying to unpick the mess to confirm/find a starting point for something sensible, regular and useful is not simple…

I can certainly see why astronomers use Julian day numbers, and why chronologies can be so contentious.

EDIT: of course our ancestors were quite smart and after some time speaking with them the answers are much clearer, especially how there is only one sensible way to use regnal years to mark time with whole values whilst retaining absolute precision… although its a bit late to work something up, I will certainly do so soon :slight_smile:

1 Like

I ended up staying up late to do the work… I had the magic numbers I needed around midnight, and I was fully intending to sleep, but instead I’ve been verifying the work and I’ve added it to the calendar as an option.

18th April would have been the calendar date for Wep Ronpet this year if the calendar was continued unaltered since Ptolemaic times.

Interestingly many astronomers ignored the Julian and Augustan calendar reforms in their work (including Claudius Ptolemy), and its not always clear how careful given Julian and Gregorian dates are in academic work either. Because of this I ended up using the 1st Thoth in Year 1 of Kleopatra VII as a reference date that I could find many sources agreeing with precisely. 1st Thoth in Year 1 of Augustus predates any reforms, but I’ve seen several different dates within a range of 4 days.

My algorithm agrees with the calculators I’ve found as well as the reconstructed table used in the Almagest, but I would like to recreate the same work in other ways to be more certain, and perhaps better understand the sources of the ambiguities in the later, Roman dates.

EDIT: the discrepancies seem to be from people using the Alexandrian calendar for the early years of Augustus, introducing a one day offset to either Julian or Gregorian proleptic dates, and resulting in the range of 4 dates that are seen. One example is clearly identifiable here: Date Converter for Ancient Egypt where 1st Thoth, Kleopatra VII year 23 does not match 1st Thoth, Augustus year 1 as it ought to.

1 Like

You are doing some seriously good research here, I think this will be a game changer !

1 Like

I have become somewhat obsessed with this… to the point of staying up past 3am (!)

It is difficult and slightly fussy work, although I’ve finally been able to push something back as far as the 26th Dynasty with much better accuracy than the web tool I linked. Dates of major events line up with regnal years correctly at least, e.g. the death of Wahibre Haaibre (Apries) during the 3rd year of Ahmose II.

I’m wondering how to expose this on the calendar… or if I should do it at all? Year numbers for current dates do not look useful, but perhaps I should add a better interface for selecting previous years? Perhaps giving a choice of era to use?

Perhaps yet another project for a date converter? Or some kind of easily browsed chronology linking to sources?

Time for bed…

EDIT: make that 25th Dynasty :smiley:

at some point soon i expect to get an ambiguity, just depends on the luck of records and how late in the year a new king came to power.

EDIT 2: 24th… now back to work for me :slight_smile:

1 Like

I spotted an eclipse whilst testing, since the curve of the moon and sun aligned around the second week of October.

Neat :slight_smile:

1 Like

That’s well spotted!!

Lucky and unlucky days added from the Cairo calendar.

Also spotted another North American eclipse on this date…


Its nice how working with this in a practical way, with visualisation makes it very easy to spot such things, without needing to do further complicated maths to specifically predict eclipses. I have a new appreciation for the wisdom of ancient astronomers in their approach, even if I have a computer to save me from doing what would be days of laborious computations once a year.

Amazing and interesting! I’ll have to have a look later. Good timing with the New Year approaching.

Happy New Year!!! I hope 2024 brings good things for everyone and for Kemeticism as a whole!

Ankh wedja seneb!


1 Like

I finally added the results of my chronology work as well.

In case anyone was interested it turns out that Ramesses III ascended the throne on a Thursday…