He evaluated the mean tropical year as 365 solar days, 5 hours, 48 minutes, 45 seconds ( 365.24219 days ) . ( Meeus & Savoie, 1992, p . 41)
12.
Since the summer solstice year ( like all equinox and solstice years ) is constantly changing it would be easier to use the mean summer solstice year ( the mean tropical year ) in the investigation.
13.
He noted that it is consistent with the tropical year of the Alfonsine tables and with the mean tropical year of Copernicus ( " De revolutionibus " ) and Reinhold ( " Prutenic tables " ).
14.
The " tropical year " in the 1960 definition was not measured but calculated from a formula describing a mean tropical year that decreased linearly over time, hence the curious reference to a specific " instantaneous " tropical year.
15.
No equinox or solstice will ever be more than a day or so away from its mean date according to the solar calendar, while nineteen Jewish years average 6939d 16h 33m 03s compared to the 6939d 14h 26m 15s of nineteen mean tropical years.
16.
The accuracy claim at Iranian calendars seems to be in error because it bases its calculation on the mean tropical year, whereas that calendar is designed ( like ours ) to keep the vernal equinox on the same date ( which their actual calendar does by observation ) ."
17.
The "'Julian calendar "', proposed by Julius Caesar in 46 BC ( 708 gradually replaced by the Gregorian calendar, promulgated in 1582 by Pope Gregory XIII . The Julian calendar gains against the mean tropical year at the rate of one day in 128 years.
18.
Is the " mean tropical year " the average of the four tropical years measured respectively starting at the vernal equinox, summer solstice, autumnal equinox and winter solstice, or is it based on a mathematical " continuous " averaging taken over all possible tropical years through the four seasons?
19.
Compare that with the mean tropical year of 365.2421897 days . That would amount to three skipped leap years every 284 years, as opposed to the present ( Gregorian ) calendar's three every 400 years . talk ) 01 : 27, 21 February 2011 ( UTC)
20.
The Gregorian calendar attempts to cause the northward equinox to fall on or shortly before March 21 and hence it follows the ppm of the current length of the mean tropical year ( days ) and even closer to the current " March equinox year " of days that it aims to match.
