Re: DBMS_UTILITY.GET_TIME

"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 Received on Tue Dec 03 2002 - 07:18:49 CST