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Erasmus Reinhold used Copernicus' theory to compute the Prutenic Tables in 1551, and gave a tropical year length of 365 solar days, 5 hours, 55 minutes, 58 seconds (365.24720 days), based on the length of a sidereal year and the presumed rate of precession. This was actually less accurate than the earlier value of the Alfonsine Tables.
As at Feb 20, 2025, solar cycle 25 is averaging 37% more spots per day than solar cycle 24 at the same point in the cycle (Feb 20, 2014). 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.
Since 1978, solar irradiance has been directly measured by satellites with very good accuracy. [11]: 6 These measurements indicate that the Sun's total solar irradiance fluctuates by +-0.1% over the ~11 years of the solar cycle, but that its average value has been stable since the measurements started in 1978.
Typical meteorological year (TMY) is a collation of selected weather data for a specific location, listing hourly values of solar radiation and meteorological elements for a one-year period. The values are generated from a data bank much longer than a year in duration, at least 12 years.
Solar cycle 25 is the current solar cycle, the 25th since 1755, when extensive recording of solar sunspot activity began. It began in December 2019 with a minimum smoothed sunspot number of 1.8. [ 2 ]
An animation of the inner Solar System planets' orbit around the Sun. The duration of the year is the time taken to go around the Sun. The year is a unit of time based on the roughly 365 1 / 4 days taken by the Earth to revolve around the Sun. [1]
Solar cycle 24 is the most recently completed solar cycle, the 24th since 1755, when extensive recording of solar sunspot activity began. [ 1 ] [ 2 ] It began in December 2008 with a minimum smoothed sunspot number of 2.2, [ 3 ] [ failed verification ] and ended in December 2019. [ 4 ]
The Islamic calendar is a purely lunar calendar and has a year, whose start drifts through the seasons and so is not a solar calendar. The Maya Tzolkin calendar, which follows a 260-day cycle, has no year, therefore it is not a solar calendar. Also, any calendar synchronized only to the synodic period of Venus would not be solar.