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From: DAVID@ches.cs.vims.edu
Newsgroups: comp.lang.pascal
Subject: Re: leap year function
Message-ID: <27162@adm.brl.mil>
Date: 10 Jun 91 19:57:46 GMT
Sender: news@adm.brl.mil
Lines: 23

Where do the elusive 0.0003 days go? I quote from "Tables of
Physical and Chemical Constants", G.W.C.Kaye & T.H.Laby, Longmans.
"The mean length of a year in this [the Gregorian] calendar is thus
365.2425 days, which is so near the present actual value that the
date when it will appear to future generations expedient to replace
one further Leap Year by an ordinary one is not yet clearly
specifiable."

The "leap seconds" have to do with the varying rate of rotation of
the _earth_ and keep the solar day in synchronism with the standard
atomic clocks. Leap years, on the other hand, have to do with the
time taken for the earth to orbit the sun.

Another nasty wrinkle about the calendar is that before the 1700's,
the year changed at dates different from January 1. Which day
dependent on which country you were in and even in one country
things changed over time. In England, for a while, things were
standardized so that March 25 (one of the quarter days) began the
year, thus March 24, 1666 was followed by March 25, 1667.
On tombstones you sometimes see dates like January 25, 1650/51.

David Evans, Virginia Institute of Marine Science
DAVID@CHES.CS.VIMS.EDU