Using Plethon’s Sacred Calendar

This page provides guidance and spreadsheets to help you determine the Sacred Month according to Plethon’s calendar.

Determining the Sacred Month

Plethon’s Sacred Month begins on the day following the conjunction of the sun and moon as determined by astronomy. Plethon calls the day of conjunction “Old-and-New” (῞Ενη καὶ Νέα, Henę kai Nea) and the following day (the first of the month) is called “New Moon” (Νουμηνία, Noumęnia). The spreadsheets provided here (in two formats) will help you to determine the dates of Plethon’s ceremonies and rituals. Fill in the date for Old-and-New immediately preceding the current month in row 2, and the date for Old-and-New following this month in row 32. (These two cells have colored backgrounds.) Write the dates in mm/dd/yyyy format. The spreadsheet will then calculate all the days of the month. In addition, it will indicate whether to include ”Old Moon” before Old-and-New if the month is full (30 days) or to omit it if it’s hollow (29 days). The spreadsheet also includes some reminders of the celebrations for the various days. You might want to upload the spreadsheet to Google Sheets, where it can be kept up to date and will be accessible on all your devices.


Determining Lunar Conjunctions (Old-and-New days)

You may find it convenient, at the end of the year, to fill in the following spreadsheet with the dates for the lunar conjunctions (Old-and-New days) for the new year. You can look up the dates on a website such as this, but beware that Old-and-New (conjunction) is called “new moon” on these sites. Fill the dates of conjunction into the column labeled “Old-and-New,” and the spreadsheet will calculate the dates of New Moon and the lengths of the months (29 or 30 days). Write the dates in mm/dd/yyyy format. Recall that Plethon’s year begins with the lunar conjunction (Old-and-New) following the winter solstice.


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Last updated: July 15, 2021