Improving datetime

[John Machin]

On Mar 22, 4:36 am, Christian Heimes <li... at cheimes.de> wrote:
> Colin J. Williams schrieb:
>
> > You might consider adding the Julian date
> > (http://en.wikipedia.org/wiki/Julian_date).
>
> > I had a crack at this a while ago but didn't seem to get quire the right
> > result, using the ACM algorithm.  I seemed to be a day out at the BC/AD
> > divide.

1. Somewhere in the Colin-Christian-Nicholas thread, the "Julian date"
and the "Julian calendar" seem to become conflated.
2. "day out": possibly because there is no year 0; year 1 BCE is
followed immediately by year 1 CE.

>
> Yes, the Julian date family is very useful when dealing with dates
> before 1900.

I'm having some difficulty understanding the above sentence, given
either interpretation of "Julian date family". What is the
significance of 1900?

[Julian calendar interpretation] Some countries (including Russia,
China, Greece and Turkey) did not adopt the Gregorian calendar until
after 1900. Dealing with a date expressed as (year, month, day) is far
from easy for approx year range 1582 to 1926 unless it has been
expressly tagged as e.g. "old style" or "new style". If so tagged,
there is to me no difference in ease of use between the proleptic
Julian calendar and the proleptic Gregorian calendar.

[Julian date as used in astronomy] This supports dates back to about
4800 BCE easily, whereas Python's datetime module supports the
proleptic Gregorian calendar only back to year 1 CE.

Cheers,
John