Two new calendar proposals: Universal Lunisolar Calendar and Universal Semiseasonal Calendar

While the Gregorian calendar, the calendar officially used by the United States, the rest of the western world, and many other countries, has served us well, it has, in my opinion, several flaws:

  • Especially in non-leap years, the second month of the year (February) is noticeably shorter than the other eleven months for no real reason.
  • September, October, November, and December, the 9th, 10th, 11th and 12th months, respectively, are actually incorrectly named: In Latin, September means “seventh month”, October means “eighth month”, November means “ninth month”, and December means “tenth month”.
  • The beginning of each year does not line up with either meteorological or astronomical seasons (i.e, the beginning of each year is not at the beginning or middle of a meteorological or astronomical season).
  • The months do not line up with the phases of the moon.

What I am proposing to solve each of these problems is a Universal Lunisolar Calendar (ULC) that accounts for both the earth’s rotation around the sun and the phases of the moon. A lunisolar calendar (in this case, a lunisolar calendar based on a tropical year) is a calendar in which a year is

Here are the basic points about the ULC:

  • The ULC year begins on January 15 of the Gregorian year of the same number, which means that each ULC year begins exactly in the middle of meteorological winter according to the U.S. federal government’s definition of meteorological winter.
  • Each non-leap year shall consist of 365 days, and each leap year shall consist of 366 days. Leap years are years in which the number of the year whose numbers are divisible by four, except for years whose numbers are divisible by 100 but not by 400.
  • The start of each month is the date in which the new moon occurs in Coordinated Universal Time (UTC).
  • In years in which the first new moon of the year falls on any day other than the first day of the year, the period from the first day of the year to the day before the date of the first new moon of the year shall compromise the month Incipereber. In years in which the new moon falls on the first day of the year, the month Incipereber does not take place.
  • The first new moon of the year marks the start of the month Unusber.
  • The second new moon of the year marks the start of the month Duober.
  • The third new moon of the year marks the start of the month Tresber.
  • The fourth new moon of the year marks the start of the month Quatuorber.
  • The fifth new moon of the year marks the start of the month Quinqueber.
  • The sixth new moon of the year marks the start of the month Sexber.
  • The seventh new moon of the year marks the start of the month September.
  • The eighth new moon of the year marks the start of the month October.
  • The ninth new moon of the year marks the start of the month November.
  • The tenth new moon of the year marks the start of the month December.
  • The eleventh new moon of the year marks the start of the month Undecimber.
  • The twelfth new moon of the year marks the start of the month Duodecimber.
  • In years in which there is a thirteenth new moon of the year, the thirteenth new moon of the year marks the start of the month Finisber. In years in which there are only twelve new moons in the year, the month Finisber does not take place.
  • Although the months of Incipereber, Finisber, and, somewhat less frequently, Duodecember are usually noticeably shorter than the other twelve months of the year (most years will feature either Incipereber or Finisber, but not both, and, in some years, either Incipereber and Finisber will consist of only a single day), this is because the start of each month (with the exception of Incipereber, which starts at the beginning of any year in which the first new moon falls on a date other than the first day of the year), begins on a date that features a new moon.
  • Just like the Gregorian calendar, there are seven days in each week: Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday.
  • The ULC year begins on the same day of the week that the Gregorian year of the same number does. This is because, under the Gregorian calendar, January 15 (start of the ULC year) always falls on the same date as January 1 (start of the Gregorian year).

Since the beginning and end dates of these months don’t usually line up with the start, middle, or end of either meteorological or astronomical seasons (with the notable exception of the first day of Incipereber roughly lining up with the middle of meteorological winter, unless the year has no Incipereber due to the new moon falling on the first day of the year, in which the first day of Unusber marks the beginning of meteorological winter), I’ve also included the concept of a dimidium, which consists of half of a ULC season. There are eight dimidiums in each year:

  • Posthibernus, the first dimidium of the year, consists of the first 45 days of the year in non-leap years and the first 46 days of the year in leap years.
  • Vernus, the second dimidium of the year, consists of the 46 days after the final day of Posthibernus (days 46-91 in non-leap years, days 47-92 in leap years).
  • Postvernus, the third dimidium of the year, consists of the 45 days after the final day of Vernus (days 92-136 in non-leap years, days 93-137 in leap years).
  • Estivus, the fourth dimidium of the year, consists of the 46 days after the final day of Postvernus (days 137-182 in non-leap years, days 138-183 in leap years).
  • Postestivus, the fifth dimidium of the year, consists of the 46 days after the final day of Estivus (days 183-228 in non-leap years, days 184-229 in leap years).
  • Autumnus, the sixth dimidium of the year, consists of the 46 days after the final day of Postestivus (days 229-274 in non-leap years, days 230-275 in leap years).
  • Postautumnus, the seventh dimidium of the year, consists of the 45 days after the final day of Autumnus (days 275-319 in non-leap years, days 276-320 in leap years).
  • Hibernus, the eighth dimidium of the year, consists of the final 46 days of the year.

My other new calendar proposal, the Universal Semiseasonal Calendar (USSC), is a solar calendar (i.e., a calendar in which a year consists of a single rotation of the earth around the sun) in which the USSC year begins on 15th day of the Gregorian year of the same number and features the eight dimidiums listed above as months.

While I highly doubt that the Gregorian calendar will be replaced for official purposes in the United States at any point in my lifetime, I’ve provided two proposals for a new calendar.

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