Jonathan wrote:
>
>On Tue, Aug 15, 2000 at 09:45:55AM -0700, Nathan Wiger wrote:
>> I don't know about this. Sounds cool, but I think we should stick to
>> something that somebody somewhere uses already. Of course, something
>> standard like 0 AD isn't bad.
>
>Standard for whom? I bet there are *millions* of Jews for whom "0 AD"
>is meaningless. s/Jews/<any other group of people who have their own
>calendar that predates christianity>/
excerpts from :
http://webexhibits.org/calendars/index.html
the Islamic calendar is based on the motion of the moon,
while the year has no connection with the motion of the earth around the
sun.
But even worse, you can't just do some math and convert a
number of seconds into a old, old date, because the old calendars
were so messed up.
Before Julius Caesar introduced the Julian calendar in 45 B.C.E.,
the Roman calendar was a mess, and much of our so-called
"knowledge" about it seems to be little more than guesswork.
Originally, the year started on 1 March and consisted of only 304
days or 10 months These 304 days were followed by an unnamed
and unnumbered winter period.
In practice it was the duty of the priesthood to keep track of the
calendars,
but they failed miserably, partly due to ignorance, partly because they
were bribed to make certain years long and other years short.
Furthermore, leap years were considered unlucky and were therefore
avoided in time of crisis, such as the Second Punic War.
The Julian calendar was introduced by Julius Caesar in 45 B.C.E.
It was in common use until the 1500s, when countries started changing
to the Gregorian calendar. However, some countries (for example,
Greece and Russia) used it into this century, and the Orthodox church in
Russia still uses it, as do some other Orthodox churches.
Modified Julian Day 0 thus started on 17 Nov 1858 (Gregorian) at 00:00:00
UTC.
(somebody threw that date out, It appears to be purely
arbitrary rather than based on some celestial event)
The calendar used throughout the world today is the Gregorian calendar.
It was proposed by Aloysius Lilius, a physician from Naples, and adopted
by Pope Gregory XIII in accordance with instructions from the Council of
Trent
(1545-1563) to correct for errors in the older Julian Calendar.
By 1582 vernal equinox had moved (1582-325)/128 days = approximately 10
days backwards (because of the Julian calendar errors)
So 10 days had to be dropped.
In the Gregorian calendar, the tropical year is approximated as
365 97/400 days = 365.2425 days. Thus it takes approximately 3300 years
for the tropical year to shift one day with respect to the Gregorian
calendar.
The approximation 365 97/400 is achieved by having 97 leap years every 400
years.
a year's length is currently 365.242190 days, but it varies.
Around 1900 its length was 365.242196 days,
and around 2100 it will be 365.242184 days.
<<< end of excerpt >>>
the further back you go in history, the less accurate your
dates will be (if you want to convert a modern calendar date
to a Roman calendar date, you'll have a TON of if-then-else's
to handle) and even then, some of it is guess work.
this seems to rule out the idea of using 0 AD as a reference date.
All calendar systems are arbitrary. there is nothing that says
solar days are a better measure than lunar months
(for a given definition of "better")
they are both celestial events, and neither one of them
has a fixed, constant, period or rate.
you could argue that one is religiously biased, or you
could simply say that most of the people developing perl
use the gregorian calendar, and the developers get to pick.
by the same token, you could say that Greenwich England
is a lousy place to define the Universal Time Zone,
(the weather is miserable, the food is terrible, and the people are rude)
but, hey, almost everyone draws the zeroeth longitude through
that city. so most time calculations are based off of the time there.
but they happen to be the first to make navigational charts
and they had to put zero somewhere.
then the term "second" is arbitrary as well.
12 hours in the day and 12 hours in the night
(because their happen to be 12 months in the year?)
60 minutes in an hour and 60 seconds in a minute.
(there are 360 degrees in a circle because there
are about 365 days in a year, and 360 divided
very very nicely. and again, it worked out that
navigation using sextants wanted to keep things
as simple as possible, so easily dividible numbers
were quite desirable.)
so its all arbitrary.
but most people developing perl use the gregorian
calendar. and it seems to be fairly widespread
as far as calendars go. and in the spirit of
"the first ones there get to define the rules",
it would seem appropriate that teh perl epoch
be based off of some event on the gregorian
calendar. given the problems with earlier calendar
systems, it should be a recent (in the relative sense
of the word recent) event.
Midnight, Jan 1, 2000, Greenwich time
seems like a good candidate.
course, if someone wants, I'm sure they could write a
module that triggers off of "use local" and can translate
time and dates from Gregorian into the Islamic or Chinese
calandar.
the problem is that, in this situation, there are an infinite
number of ways to do it.
timekeeping: solar/lunar/etc
zero point: religious/secular/celestial/
zero time zone: greenwich/random/California
etc, etc, etc....
and this is the kind of mess you get.
Greg London
