Re: Microsoft to force new Outlook on Windows 10 PCs

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.)