Although this is closer to the mean tropical year of 365.24219 days, his proposal has never been adopted, and never will be, because the Gregorian calendar is based on the mean time between vernal equinoxes ( currently 365.2424 days ) and because these observed values are currently increasing.
22.
Even with this intercalation, the average Hebrew calendar year is longer by about 6 minutes and 40 seconds than the current mean tropical year, so that every 216 years the Hebrew calendar will fall a day behind the current mean tropical year; and about every 231 years it will fall a day behind the mean Gregorian calendar year.
23.
Even with this intercalation, the average Hebrew calendar year is longer by about 6 minutes and 40 seconds than the current mean tropical year, so that every 216 years the Hebrew calendar will fall a day behind the current mean tropical year; and about every 231 years it will fall a day behind the mean Gregorian calendar year.
24.
The astronomer's mean tropical year which is averaged over equinoxes and solstices is currently 365.24219 days, slightly shorter than the average length of the year in most calendars, but the astronomer's value changes over time, so William Herschel's suggested correction to the Gregorian calendar may become unnecessary by the year 4000.
25.
The three mean tropical years in Babylonian sexagesimals as the excess over 365 days ( the way they would have been extracted from the tables of mean longitude ) were 14, 33, 9, 57 ( Alphonsine ), 14, 33, 11, 12 ( Copernicus ) and 14, 33, 9, 24 ( Reinhold ).
26.
As 218 out of every 900 years are leap years, the average ( mean ) length of this Julian year is days, which is closer to the length of the mean tropical year, days, than is the Gregorian mean year, 365.242 5 days . In the year 2800 CE, the Gregorian and Revised Julian calendars will begin to differ by one calendar day.
27.
The rules are based on the theory that Maimonides explains in his book " Rabbinical Astronomy "-no allowance is made for the secular ( centennial ) decrease of ?second in the length of the mean tropical year and the increase of about four yards in the distance between the earth and the moon resulting from tidal friction because astronomy was not sufficiently developed in the 12th century ( when Maimonides wrote his book ) to detect this.
28.
:: Yes, the winter solstice was used by earlier civilisations, but the current system uses the mean time between vernal equinoxes which is currently approximately 365.2424 days ( and gradually increasing ), compared with the mean tropical year of 365.24219 days . Sir John Herschel's correction ( for the year 4000 ) might never be necessary ( even if we are still here and still use a calendar then ).
29.
The product of Simon Newcomb's J1900.0 mean tropical year of ephemeris seconds and a speed of light of produced a light-year of ( rounded to the seven significant digits in the speed of light ) found in several modern sources was probably derived from an old source such as C . W . Allen's 1973 " Astrophysical Quantities " reference work, which was updated in 2000, including the IAU ( 1976 ) value cited above ( truncated to 10 significant digits ).
30.
But ( according to von M�dler ) if the years 3200, 6400, 9600, 12, 800, 16, 000 and so on are NOT leap years the duration of the mean Gregorian year will then be 365.2421875 days ( 10, 000 divided by 3200 gives 3.125 ) and this approaches very closely the real duration of the mean tropical year which lasts 365.24219 days . So that a very little error of only 3.125-3.100 = 0.025 days in 10, 000 years will then be made.
