Re: DBMS_UTILITY.GET_TIME

From: Paul Brewer <paul_at_paul.brewers.org.uk>
Date: Tue, 3 Dec 2002 21:20:59 -0000
Message-ID: <3ded2d8a_2@mk-nntp-1.news.uk.worldonline.com>

"Richard Foote" <richard.foote_at_bigpond.com> wrote in message news:141H9.89399$g9.250705_at_newsfeeds.bigpond.com...
> "Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message
> news:vB_G9.89226$g9.250834_at_newsfeeds.bigpond.com...
> > Oracle's epoch isn't actually arbitrary at all. In fact, it's midnight
on
> > December 31st 4713BC (or, as the doco. puts it, January 1st 4712BC) for
> > three very good reasons.
> >
> > Every 28 years, the same day of the week falls on the same date
throughout
> > the calendar. That's called the Solar Cycle. (It can be calculated as
> (year
> > + 8) mod 28 + 1 -hence 2002 is Solar Cycle number 15).
> >
> > Every 19 years, the phases of the moon fall on the same dates. That's
> called
> > the Golden Number, and each year it goes up by one, until it reaches 19,
> and
> > then it resets. For two year 1's, for example, the new moon falls on the
> > same day of each month for both years. It can be calculated as (year mod
> > 19)+1 -hence 2002 has Golden Number 8)
> >
> > On 1st September 312, Constantine the Great created a new tax based on a
> 15
> > year cycle (and it fell into disuse in 1806, strangely enough), called
the
> > Indiction. Each year can be given a number between 1 and 15 depending on
> > where it falls in the Indiction cycle. It can be calculated as ((year+2)
> mod
> > 15) + 1 -hence 2002 has Indiction number 4).
> >
> > Justus Scaliger (1540-1609) was a French mathematician (his father was
> > called Julius Caesar Scaliger) who decided to create a comprehensive
> > numbering system for every year imaginable. The numbering system he
> devised
> > is called the Julian Period, probably after his father. His Julian
Period
> > starts on January 1st 4713BC and lasts 7980 years. Why? Because,
counting
> > backwards and doing a bit of juggling, in 4713BC the Solar Cycle number
> was
> > 1, as was the Golden Number, as was the Indiction. If you multiply 19 by
> 15
> > by 28, you get 7980 -meaning that in 3268AD (being 7980 years on from
> > 4713BC) the Julian Number will recycle back to 1 again for the first
time
> > since 4713BC.
> >
> > Astronomers have taken the Julian numbering system and extended it so
that
> > every *day* since January 1st 4713BC gets its own Julian number, with
> > January 1st 4713BC itself being designated Day Zero. Jnuary 1st 2000 AD
> was
> > therefore Julian Day 2,451,545. (that's 6712 years sine 4713BC,
multiplied
> b
> > y 365.25 days per year, less the 13 days that the Gregorian Calendar is
> > ahead of the Julian (ie, the real Julius Ceasar's) Calendar).
> >
> > Just out of interest, Oracle has varied the Julian Period a bit: it's
year
> > count recycles on December 31st 4713 AD, not 3268 AD. So we have an
extra
> > 1445 years before we have to worry about what happens when they *do*
> > recycle. It is true, however, that every Oracle database on the planet
is
> > facing the potential problem of the 'year 4713 problem'. Not that I
think
> we
> > need get too worked up about it just yet!!
> >
> > Fascinating stuff, I'm sure you'll agree... point is, it's definitely
> *not*
> > an 'arbitrary' epoch.
> >
> > Regards
> > HJR

>

> Hi Howard,

>

> Speaking of time, you have way too much time on your hands .....

>

> Cheers ;)

>

> Richard

>
>
Too much time?

Until to_date('31/12/1999 23:59:59','DD/MM/YYYY HH24:MI:SS'), we did. Now, of course, the business people think the whole Y2K thing was a huge bluff, contrived to allocate budgets to the IT department. Very little went wrong, thanks to our efforts, so of course the whole thing was a false alarm engineered by the IT department, just to claim resources.

Bitter? Moi?

Regards,
Paul Received on Tue Dec 03 2002 - 15:20:59 CST