A calendrical table

Gregorian: Roman-derived Christian solar calendar now used secularly the world over. Days start at midnight. Months start on arbitrary dates, lasting 28–31 days each depending on the month. Years start on 1 January, a few days after the northern winter solstice. A leap day, 29 February, is added every four years, except for years which are divisible by 100 but not 400. Epoch a few years after the birth of Jesus of Nazareth; Ol. ρϟδʹ.δʹ in Attic. Numbers here written using Hindu-Arabic numerals.

Attic: Ancient Athenian lunisolar festival calendar now used liturgically by contemporary Hellenic Pagans. Days start at sunset. Months start on new moons, lasting 29–30 days each. On the twenty-first day of the month, dates start counting down from 9 instead of up, here marked with a ☾ waning crescent moon. Years start on αʹ He­ca­tom­bæon, the first new moon after the northern summer solstice. The month of Po­sei­deon is doubled in years with thirteen new moons. Epoch at first ancient Olympic games; 776 BCE in Gregorian. Numbers here written using Greek numerals; years here written as [Olympiad].[Year].

Holidays: This column serves as a liturgical calendar of relevant Greek and Roman festivals. I’ve also included the solstices and equinoxes, as well as the Wiccan Wheel of the Year (for the benefit of any avid syncretists reading), the occasional secular commemoration (such as Bonfire Night), and some Christian holidays (seeing as the continent is 64% Christian, their calendar still holds quite some weight to the daily lives of even the most stridently secular Britons and Dutchfolk). Underlined festivals are reckoned by the Attic calendar and last from sunset to sunset rather than midnight-to-midnight. Festivals marked with an asterisk* have had their precise occurrences lost in the fog of history, so their dates here are the result of some conjecture.

All dates given have been calibrated for the north of England. They may be inaccurate for other regions, especially in the southern hemisphere, where the solstices and equinoxes are reversed.