Subject | Re: [firebird-support] Internal Date Format |
---|---|

Author | Doug Chamberlin |

Post date | 2003-07-03T22:23:15Z |

At 7/3/2003 04:47 PM (Thursday), Martijn Tonies wrote:

believe DEC chose it because they had to choose something and it was

already in use. (I think one key market for VAX/VMS was the systems market

dominated by Control Data Corp for computers which would conveniently

handle very large numbers. Their machines had 48 and 60 bit words. I know

the Smithsonian Astronomical Observatory was one of the first users of

VAX/VMS systems and replaced one or more CDC machines with one or more

VAX/VMS machines.)

From http://www.iwpcug.org/docs/18991230.htm :

Astronomers, for example, use 17 November 1858 as day zero for a date known

as MJD = Modified Julian Date. This is actually a modification in smaller

numbers of another day number system called the Julian Date which has a

zero at noon on 1 January 4713 BC of the Julian Proleptic Calendar. That

date is 2,400,000.5 days prior to 0 hours on 17 November 1858.

The Julian Proleptic Calendar, in case you wondered, is the Julian Calendar

extended backwards in time following the same rules as the Julian Calendar

regarding leap years; i.e. every four years without any exceptions. In this

calendar, there is no year zero so that 1 BC is the year prior to 1 AD.

This has the unfortunate consequence that leap years prior to 1 AD are not

those divisible by four but those years which have a remainder of one when

divided by four. Thus the year 4713 BC in this calendar was a leap year.

The days of the week continue without exception in their cycle of seven

days and if you work it out, 1 January 4713 BC was a Monday. This date was

chosen by an Italian named Joseph Scaliger (1540-1609) as preceding all

astronomical events known at that time so that all Julian Dates are positive.

> > The first longword is the number of days since 17 November 1858.I believe Interbase used this date because the VAX/VMS system used it. I

> > (That's a long story).

>

>Care to do a write up and add it to the History part at cvalde.com?

>

>I'm curious :)

believe DEC chose it because they had to choose something and it was

already in use. (I think one key market for VAX/VMS was the systems market

dominated by Control Data Corp for computers which would conveniently

handle very large numbers. Their machines had 48 and 60 bit words. I know

the Smithsonian Astronomical Observatory was one of the first users of

VAX/VMS systems and replaced one or more CDC machines with one or more

VAX/VMS machines.)

From http://www.iwpcug.org/docs/18991230.htm :

Astronomers, for example, use 17 November 1858 as day zero for a date known

as MJD = Modified Julian Date. This is actually a modification in smaller

numbers of another day number system called the Julian Date which has a

zero at noon on 1 January 4713 BC of the Julian Proleptic Calendar. That

date is 2,400,000.5 days prior to 0 hours on 17 November 1858.

The Julian Proleptic Calendar, in case you wondered, is the Julian Calendar

extended backwards in time following the same rules as the Julian Calendar

regarding leap years; i.e. every four years without any exceptions. In this

calendar, there is no year zero so that 1 BC is the year prior to 1 AD.

This has the unfortunate consequence that leap years prior to 1 AD are not

those divisible by four but those years which have a remainder of one when

divided by four. Thus the year 4713 BC in this calendar was a leap year.

The days of the week continue without exception in their cycle of seven

days and if you work it out, 1 January 4713 BC was a Monday. This date was

chosen by an Italian named Joseph Scaliger (1540-1609) as preceding all

astronomical events known at that time so that all Julian Dates are positive.