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From: Physfitfreak <physfitfreak@gmail.com>
Newsgroups: alt.comp.os.windows-10,comp.os.linux.advocacy
Subject: Re: Microsoft to force new Outlook on Windows 10 PCs
Date: Fri, 17 Jan 2025 16:00:55 -0600
Organization: Modern Human
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On 1/17/25 7:03 AM, Farley Flud wrote:
> I believe that Julian Dates (JD) are used for this purpose.  The JD
> is a count of the number of days since January 1, 4713 BCE.


Even if you accurately count the number of days past since, say, the day 
with date 1/17/1700, it won't mean you have all the information about 
that day's correct location in that year; because, Earth's tilted axis 
of rotation is not along a fixed direction. The axis wobbles, or 
"precesses" all the time. So a historian who wrote down the date as 
1/17/1700 on that day, will slightly be in a different time of the year 
compared to the present day's 1/17/2025.

As long as the difference falls below one day, this is not that 
important. But if you go back farther in time to Darius's era, this 
difference places you in a different season of the year. A historian who 
according to your calculations would've written down the date 1/17/-1500 
in his notes, was not on the January 17th of that year! He was in 
another season of that year. Therefore your calculated result of 
1/17/-1500 is meaningless.

This may look a rather simple astronomy problem, but when you want to 
program it, it gets tough sometimes. And there are options to take to 
correct the discrepancies. I took the option of modifying the length of 
a day just enough to take care of precession of the axis of rotation of 
Earth, as well as of course its orbiting around the sun (which by itself 
introduces one day of discrepancy per year.)