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eftychia: Me in kilt and poofy shirt, facing away, playing acoustic guitar behind head (Default)
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QotD

posted by [personal profile] eftychia at 05:26am on 2007-10-22

"I doubt the [ISO] description of the average duration of the Calendar Year.

"ISO 8601:2004 2.2.13 has 'calendar year   cyclic time interval in a calendar which is required for one revolution of the Earth around the Sun and approximated to an integer number of calendar days'. ISO 8601:2000 3.30 had similar wording.

"Taken literally, that revolution can only be with respect to the 'Fixed Stars'. But the fundamental requirement on the Calendar Year from time immemorial is that it should be locked to the cycle of the four seasons; it is that which governs the provision of leap years. The seasons are caused by the tilt of the Earth's axis with respect to its orbital plane. The axis slowly precesses, and that is generally described by the Precession of the Eqinoxes; the period is about 25800 years. The difference is 39 ppm, about twice the Gregorian Correction."

-- Dr. J.R. Stockton, "Date and Time Formats"

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There are 3 comments on this entry. (Reply.)
 

(no subject)

posted by [identity profile] juuro.livejournal.com at 10:21am on 2007-10-22
The good doctor is guilty of oversimplification when he claims that the cycle of the seasons governs the provision of leap years. Already the clause "[calendar year is] approximated to an integer number of calendar days" will require the intermittent correction of the leap years. In times and cultures where the calendar was indeed kept in sync with the seasons, the intercalation schemes often included both leap and fall years; sometimes a month or even two would be added, sometimes a month would be omitted.

Seasonal synchronisation is, indeed, a desirable property for a timekeeping scheme for planetary use. But to have a Galactic, or in the fullness of time, a Multiversal calendar that is subject to parochial oddities of one planet... will sound to me as lacking vision.
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(no subject)

posted by [identity profile] scruffycritter.livejournal.com at 09:44pm on 2007-10-22
I'm not sure. I read that as rounding because the calendar year doesn't get divided evenly by a fixed number of calendar days.

The current system is desingned to keep our dates sync'd to where the planet is in relation to the sun. We round so we always are at point X and a certain calendar date....but if the good doctor is right, the Earth's axial tilt doesn't follow it. Assuming he's right, one day July 1 will not be in summertime, leap year introductions or not.

Until we find a planet that has a "day" than can always always always be divided evenly into it's "days in a year" number, youre right, we can't do that. But none of our definitions has ever worked for that purpose.
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redbird: closeup of me drinking tea, in a friend's kitchen (Default)

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posted by [personal profile] redbird at 11:39am on 2007-10-22
As [livejournal.com profile] juuro says, if you want a whole number of days, you're stuck with leap years. But locking it to the cycle of the seasons isn't from "time immemorial," because we know when Julius Caesar lived, and when Hillel did. (Unless "time immemorial" here is the term of art from English law.)

This isn't where the difference between sidereal and solar time gets most interesting, though. The solar year on Mercury is twice the length of the sidereal one. (The 88 days you'll see for the length of the Mercurian year is sidereal.)
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