Horological Meandering

Only some WESTERNERS might use the 31 Dec 23 if they are on the "normal" calendar, but many calendars exist even today, as you move around the world.  (See TIME & DATE site)

Calendars Worldwide include: 

Gregorian Calendar  (the main international calendar used for civil / government / secular dates)

Julian Calendar was used into the 1900s by the West and still by Orthodox churches in Russia & Mt Athos for religious events and holidays

Hindu Calendar (Indian National Calendar or Saka Calendar, the official standardized calendar of India since 1957, represents but one of many variations of the Hindu calendar.)

Buddhist Calendar (this lunisolar calendar tracks movements of both the Moon and the Sun and is related to the Hindu calendar) Some Buddhist festivals are calculated using this calendar.

Islamic Calendar - a lunar calendar whose time reckoning is tied to the Moon phases. The timing of the months in the Islamic calendar is based on astronomical observation. A new month can only begin after a Waxing Crescent Moon is observed shortly after sunset. Unlike other calendar systems that use leap days or leap months to synchronize the calendar with the solar year, the Islamic calendar is completely detached from astronomical seasons marked by the equinoxes and solstices. An Islamic year consistently falls about 11 days short of the solar year.

Jewish Calendar - This lunisolar calendar keeps in sync with the natural cycles of both the Sun and the Moon. Featuring a body of complex regulations, exceptions, and mathematical rules, it is also designed to satisfy a number of requirements conveyed in the Jewish Holy Scripture. Using the lunar rules means it is off the solar year by 1 day every 216 years.

Persian (Iranian/Afghan) Calendar - the Solar Hijri calendar is based on astronomical observations. The year begins at midnight closest to the vernal equinox in Iran—specifically at the Iran Standard Time meridian at longitude 52.5° east, which runs about 250 miles (400 km) east of Tehran. The first day of the new year is called Nowruz, and it is celebrated around the world by Iranian people. Being based on observation keeps the astronomical seasons consistent compared to the Gregorian calendar,which deviates from the solar year by 1 day in 3236 years, needs leap corrections, etc.

Chinese Calendar - Lunisolar and based on exact astronomical observations of the Sun's longitude and the Moon's phases. It attempts to have its years coincide with the tropical year and shares some similarities with the Jewish calendar. In both these calendars, a common year has 12 months and a leap year has 13 months; and an ordinary year has 353–355 days while a leap year has 383–385 days.

Baháí Calendar - divides the year into nineteen months of nineteen days each. The total of 361 days is supplemented by four or five intercalary, or extra, days which are added to harmonize the calendar with the Earth's movements around the Sun. To create a globally uniform system, the new year always begins at sunset on March 20, despite the fact that the vernal equinox may occur on March 20, 21 or 22. These changes keep the Badi calendar in harmony with the Gregorian calendar, and came into effect at the start of the Bahai year 172 BE, or 2015 CE.

Coptic Calendar The Coptic calendar year is divided into 13 months. The first 12 months have 30 days. The last month, called Pi Kogi Enavot or Nasie and referred to as an epagomenal month, has 5 days in a common year and 6 days in a leap year. It is also called the Alexandrian calendar, but is neither to be confused with the ancient Egyptian calendar, from which it derives, nor with the Ethiopian calendar, which is closely related but uses different year numbers.

Ethiopian Calendar A year in the Ethiopian calendar is 13 months long, with 12 months of 30 days each. The last month has 5 days in a common year and 6 days during leap year. Like in the Julian calendar, a leap year in the Ethiopian calendar happens every 4 years without exception. The main point of difference lies in the calculation of the date of the birth of Jesus, which means that the Ethiopian calendar is 7 to 8 years behind the Gregorian calendar year date. While most Christians celebrate Christmas on December 25, Ethiopians celebrate Christmas on January 7 along with many Orthodox Christian churches around the world.

etc.

How do I know this? I used to write Mathematics textbooks, and calendars fall into Math in school.

Cazalea

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