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  2. List of solar cycles - Wikipedia

    en.wikipedia.org/wiki/List_of_solar_cycles

    An example is the Meeus smoothing formula, [7] with related solar cycles characteristics available in this STCE news item. [8] The start of solar cycle 25 was declared by SIDC on September 15, 2020 as being in December 2019. [9] This makes cycle 24 the only "11-year solar cycle" to have lasted precisely 11 years.

  3. 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. [1]

  4. Solar cycle - Wikipedia

    en.wikipedia.org/wiki/Solar_cycle

    The Solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surface. Over the period of a solar cycle, levels of solar radiation and ejection of solar material, the number and ...

  5. Solar calendar - Wikipedia

    en.wikipedia.org/wiki/Solar_calendar

    The mean calendar year of such a calendar approximates the sidereal year. Leaping from one lunation to another, but one Sidereal year is the period between two occurrences of the sun, as measured by the stars' solar calendar, which is derived from the Earth's orbit around the sun every 28 years. [3]

  6. Lunisolar calendar - Wikipedia

    en.wikipedia.org/wiki/Lunisolar_calendar

    A lunisolar calendar is a calendar in many cultures, that combines monthly lunar cycles with the solar year. As with all calendars which divide the year into months, there is an additional requirement that the year have a whole number of months (Moon cycles).

  7. Tropical year - Wikipedia

    en.wikipedia.org/wiki/Tropical_year

    the period of time for the ecliptic longitude of the Sun to increase 360 degrees. Since the Sun's ecliptic longitude is measured with respect to the equinox, the tropical year comprises a complete cycle of seasons, and its length is approximated in the long term by the civil (Gregorian) calendar.

  8. Maya calendar - Wikipedia

    en.wikipedia.org/wiki/Maya_calendar

    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.

  9. Equinox - Wikipedia

    en.wikipedia.org/wiki/Equinox

    The dates of the equinoxes change progressively during the leap-year cycle, because the Gregorian calendar year is not commensurate with the period of the Earth's revolution about the Sun. It is only after a complete Gregorian leap-year cycle of 400 years that the seasons commence at approximately the same time.