[Info-vax] Why is starting epoch 17 Nov 1858?

[VAXman- at SendSpamHere.ORG]

In article <s2aqvh$o7s$1 at dont-email.me>, Stephen Hoffman <seaohveh at hoffmanlabs.invalid> writes:
>On 2021-03-10 14:21:17 +0000, David Jones said:
>
>> On Tuesday, March 9, 2021 at 3:02:13 PM UTC-5, Jim DeCamp wrote:
>>> On Monday, November 27, 1995 at 3:00:00 AM UTC-5, 
>>> zrep... at cuppa.curtin.edu.au wrote:
>>> It's called Smithsonian time, and yes it is the epoch for the Modified 
>>> Julian Day, which is the Julian Day minus 2,400,000.5 days.
>> 
>> Is that 2400000.5 magic number ensconced in a header file symbol 
>> definition anywhere?
>
>It's been a while since I've looked at that code, but I wouldn't expect 
>to see that value around other than in comments, as it is immaterial to 
>the process of converting to and from the base date.
>
>Converting from 0 is 17-Nov-1858, and from 17-Nov-1858 produces 0. A 
>day's accumulated centiseconds gets you 18-Nov-1858, obviously.
>
>That there's a second and earlier date with a nice round offset from 
>the any base date isn't any more relevant to the conversion process 
>than would be a nice round offset date after the base date.
>
>Neither the Smithsonian base date nor the Gregorian base date is 
>anything other than a convenience, particularly given we don't know the 
>offset from the Big Bang (yet?), and usually wouldn't want to store it 
>everywhere anyway.

That might require implementation of  planck-time units and many many 
many more bits than current implementations possess. ;)

-- 
VAXman- A Bored Certified VMS Kernel Mode Hacker    VAXman(at)TMESIS(dot)ORG

I speak to machines with the voice of humanity.