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Doomsday rule. The Doomsday rule, Doomsday algorithm or Doomsday method is an algorithm of determination of the day of the week for a given date. It provides a perpetual calendar because the Gregorian calendar moves in cycles of 400 years. The algorithm for mental calculation was devised by John Conway in 1973, [ 1][ 2] drawing inspiration from ...
The sexagenary cycle, also known as the stems-and-branches or ganzhi ( Chinese: 干支 ), is a cycle of sixty terms, each corresponding to one year, thus a total of sixty years for one cycle, historically used for recording time in China and the rest of the East Asian cultural sphere and Southeast Asia. [1] [2] It appears as a means of ...
A perpetual calendar is a calendar valid for many years, usually designed to look up the day of the week for a given date in the past or future. For the Gregorian and Julian calendars, a perpetual calendar typically consists of one of three general variations: Fourteen one-year calendars, plus a table to show which one-year calendar is to be ...
The Sothic cycle or Canicular period is a period of 1,461 Egyptian civil years of 365 days each or 1,460 Julian years averaging 3651⁄4 days each. During a Sothic cycle, the 365-day year loses enough time that the start of its year once again coincides with the heliacal rising of the star Sirius ( Ancient Egyptian: spdt or Sopdet, 'Triangle ...
Dominical letters or Sunday letters are a method used to determine the day of the week for particular dates. When using this method, each year is assigned a letter (or pair of letters for leap years) depending on which day of the week the year starts. The Dominical letter for the current year 2024 is GF . Dominical letters are derived from the ...
The remainder is 44.86849 years, which is 44 years and 317 days. The full year date is 644 CE. Now calculate the month and day number, taking into account leap days over the 44 years. In the Gregorian Calendar, every fourth year is a leap year with the exception of centuries not evenly divisible by 400 (e.g. 100, 200, 300).
A woman whose menstrual cycles ranged in length from 30 to 36 days would be estimated to be infertile for the first 11 days of her cycle (30-19=11), to be fertile on days 12–25, and to resume infertility on day 26 (36-10=26). When used to avoid pregnancy, such fertility awareness-based methods have a typical-use failure rate of 25% per year. [15]
The Maya calendar consists of several cycles or counts of different lengths. The 260-day count is known to scholars as the Tzolkin, or Tzolkʼin. [ 5] The Tzolkin was combined with a 365-day vague solar year known as the Haabʼ to form a synchronized cycle lasting for 52 Haabʼ called the Calendar Round. The Calendar Round is still in use by ...