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  2. Tropical year - Wikipedia

    en.wikipedia.org/wiki/Tropical_year

    The length of the tropical year was given as 365 solar days 5 hours 49 minutes 16 seconds (≈ 365.24255 days). This length was used in devising the Gregorian calendar of 1582. [7] In Uzbekistan, Ulugh Beg's Zij-i Sultani was published in 1437 and gave an estimate of 365 solar days 5 hours 49 minutes 15 seconds (365.242535 days). [8]

  3. Solar calendar - Wikipedia

    en.wikipedia.org/wiki/Solar_calendar

    The oldest solar calendars include the Julian calendar and the Coptic calendar. They both have a year of 365 days, which is extended to 366 once every four years, without exception, so have a mean year of 365.25 days. As solar calendars became more accurate, they evolved into two types.

  4. List of solar cycles - Wikipedia

    en.wikipedia.org/wiki/List_of_solar_cycles

    This makes cycle 24 the only "11-year solar cycle" to have lasted precisely 11 years. Details of cycles 1 to 25 ... averaged 71% more spots per day than year 5 of SC24.

  5. 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]

  6. Solar cycle 25 - Wikipedia

    en.wikipedia.org/wiki/Solar_cycle_25

    As at Oct 13, 2024, solar cycle 25 is averaging 40% more spots per day than solar cycle 24 at the same point in the cycle (Oct 13, 2013). Year 1 of SC25 (Dec 2019 to Nov 2020) averaged 101% more spots per day than year 1 of SC24. Year 2 of SC25 (Dec 2020 to Nov 2021) averaged 7% more spots per day than year 2 of SC24.

  7. History of astronomy - Wikipedia

    en.wikipedia.org/wiki/History_of_astronomy

    It is available in two recensions, one belonging to the Rig Veda, and the other to the Yajur Veda. According to the Vedanga Jyotisha, in a yuga or "era", there are 5 solar years, 67 lunar sidereal cycles, 1,830 days, 1,835 sidereal days and 62 synodic months. During the 6th century, astronomy was influenced by the Greek and Byzantine ...

  8. Formation and evolution of the Solar System - Wikipedia

    en.wikipedia.org/wiki/Formation_and_evolution_of...

    By 3.5 billion years from now, Earth's surface conditions will be similar to those of Venus today. [117] Relative size of the Sun as it is now (inset) compared to its estimated future size as a red giant. Around 5.4 billion years from now, the core of the Sun will become hot enough to trigger hydrogen fusion in its surrounding shell. [118]

  9. Chinese calendar - Wikipedia

    en.wikipedia.org/wiki/Chinese_calendar

    For example, one solar year of the 1st century BCE TàichÅ« calendar is 365 + 385 ⁄ 1539 (365.25016) days. A solar year of the 13th-century Shòushí calendar is 365 + 97 ⁄ 400 (365.2425) days, identical to the Gregorian calendar. The additional .00766 day from the TàichÅ« calendar leads to a one-day shift every 130.5 years. Pairs of solar ...