Re: Number of days since 1/1/0001
Re: Number of days since 1/1/0001
- Subject: Re: Number of days since 1/1/0001
- From: Bill Briggs <email@hidden>
- Date: Fri, 23 Nov 2001 21:06:51 -0400
At 7:20 PM -0500 23/11/01, Jason Bourque wrote:
Just multiple the number of years by 365 then add the days of this year
passed. Then divide the number of years by 4 and add that number from the
total number of days to count for leap year. Tada, there you go.
It's not that simple. You've accounted for leap years, but century
years would also be leap years in your calculation, but they don't
have a February 29th unless they are divisible by 400, because after
a century of corrections by leap years, it's overcorrected. In other
words, every year that is exactly divisible by 4 is a leap year,
except for years that are exactly divisible by 100; these centurial
years are leap years only if they are exactly divisible by 400. So
your method doesn't work. I forget now, but there may be another
correction factor if you go back more than 2000 years. This all has
to do with the way the rotational period of the earth around the sun
relates to the period of rotation of the earth on its axis, and you
can bet your boots that this number doesn't divide evenly, and there
will be drift over time that requires the addition of "correction
factors", which in this case are days added or removed in the form of
leap years, or "should-be" leap years that don't. Was that clear?
The issue here is that "doing the date math" is not straight
forward. The clock register on modern Macs can handle dates back to
about 30,000 years BCE (I forget the exact number, but it's very
close to that), but AppleScript is reluctant to let you work with
dates of that period. I've not tried to work around this as nothing
I've ever done has called for dates of that vintage. There may be a
workaround. But this doesn't address the problem at all. There are
code samples on the net for doing calendrics in a variety of
programming languages, but these won't illuminate the problem for you
unless you're adept at one of them. But if you're curious it's worth
having a look at the scope of calendar issues. The fact that it's
changed a number of times in history, and that different cultures use
different calendars doesn't help make it easy. You'll soon discover
that when peering into history, our modern date references soon lose
relevance, except in as much as they relate to astrological time
relative to ours. Even that's a shaky assertion. Sorting out "when"
an event happened BCE means first sorting out what you mean by
"when". Confused yet?
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