On 2009 Aug 14, at 20:32 , Joshua Schwartz wrote:
Check out my calendar blog at iosuariancalendar.blogspot.com! If you have any questions about my calendar, please contact me.
Joshua:
The Symmetry454 calendar mean year is intended to approximate the mean northward equinoctial year of 365 days 5 hours 49 minutes 0 seconds, because it is intended as a reform of the Gregorian calendar, which has that equinox as its intended target. Its 293-year leap cycle yields a calendar mean year of 365 days 5h 48m 56+152/293s, which is intentionally just slightly shy of the above target, to allow for future tidal slowing of the Earth rotation rate.
Your Iosurarian calendar mean year of 365 days, 5 hours, 48 minutes, 49.19... seconds is appreciably shorter than the mean northward equinoctial year, and it is a few seconds longer than the present era mean tropical year. The mean tropical year is irrelevant to calendars, as it is measured in atomic days, not the mean solar days that are required for civil calendars. There is no equinox or solstice associated with the mean tropical year, so there is no definitive event to establish that your calendar is accurate.
Fixed arithmetic calendar accuracy can never endure indefinitely, because the lengths of the equinoctial and solstitial years are not fixed, they vary cyclically with a general trend towards shorter years due to tidal slowing of the Earth rotation rate, see <http://www.sym454.org/seasons/>.
-- Irv Bromberg, Toronto, Canada
