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  2. Solar cycle (calendar) - Wikipedia

    en.wikipedia.org/wiki/Solar_cycle_(calendar)

    The solar cycle is a 28-year cycle of the Julian calendar, and 400-year cycle of the Gregorian calendar with respect to the week. It occurs because leap years occur every 4 years, typically observed by adding a day to the month of February, making it February 29th. There are 7 possible days to start a leap year, making a 28-year sequence.

  3. 2012 phenomenon - Wikipedia

    en.wikipedia.org/wiki/2012_phenomenon

    The 2012 phenomenon was a range of eschatological beliefs that cataclysmic or transformative events would occur on or around 21 December 2012. This date was regarded as the end-date of a 5,126-year-long cycle in the Mesoamerican Long Count calendar, and festivities took place on 21 December 2012 to commemorate the event in the countries that ...

  4. Solar cycle - Wikipedia

    en.wikipedia.org/wiki/Solar_cycle

    The Suess cycle, or de Vries cycle, is a cycle present in radiocarbon proxies of solar activity with a period of about 210 years. It was named after Hans Eduard Suess and Hessel de Vries . [48] Despite calculated radioisotope production rates being well correlated with the 400-year sunspot record, there is little evidence of the Suess cycle in ...

  5. Metonic cycle - Wikipedia

    en.wikipedia.org/wiki/Metonic_cycle

    In the Babylonian and Hebrew lunisolar calendars, the years 3, 6, 8, 11, 14, 17, and 19 are the long (13-month) years of the Metonic cycle. This cycle forms the basis of the Greek and Hebrew calendars. A 19-year cycle is used for the computation of the date of Easter each year. The Babylonians applied the 19-year cycle from the late sixth ...

  6. Lunar calendar - Wikipedia

    en.wikipedia.org/wiki/Lunar_calendar

    A lunar calendar is a calendar based on the monthly cycles of the Moon 's phases ( synodic months, lunations ), in contrast to solar calendars, whose annual cycles are based on the solar year. The most widely observed purely lunar calendar is the Islamic calendar. [a] A purely lunar calendar is distinguished from a lunisolar calendar, whose ...

  7. List of solar cycles - Wikipedia

    en.wikipedia.org/wiki/List_of_solar_cycles

    List of solar cycles. Solar cycles are nearly periodic 11-year changes in the Sun 's activity that are based on the number of sunspots present on the Sun's surface. The first solar cycle conventionally is said to have started in 1755. The source data are the revised International Sunspot Numbers (ISN v2.0), as available at SILSO. [1]

  8. Runic calendar - Wikipedia

    en.wikipedia.org/wiki/Runic_calendar

    A Runic calendar (also Rune staff or Runic almanac) is a perpetual calendar, variants of which were used in Northern Europe until the 19th century. A typical runic calendar consisted of several horizontal lines of symbols, one above the other. Special days like solstices, equinoxes, and celebrations (including Christian holidays and feasts ...

  9. Perpetual calendar - Wikipedia

    en.wikipedia.org/wiki/Perpetual_calendar

    A perpetual calendar employs a table for finding which of fourteen yearly calendars to use. A table for the Gregorian calendar expresses its 400-year grand cycle: 303 common years and 97 leap years total to 146,097 days, or exactly 20,871 weeks. This cycle breaks down into one 100-year period with 25 leap years, making 36,525 days, or one day ...