[gmiller123456]

Astronomers use "Julian Days" and "Julian Dates", but they are not at all based on the Julian calendar. They are just a linear count of days which is easier to plug in to algorithms. It is quite similar to the Unix Timestamp, and it is quite easy to convert between the two: jd =(unixT / 86400) + 2440587.5; [1].

But astronomers have to deal with the non-uniform, unpredictable rotation of the Earth in some way. Leap seconds only help a little, and predictions can only be made a few months into the future, so it is necessary to download the latest Earth Orientation data from the International Earth Rotation Service [2].

E.g. For the Apr 8 2024 solar eclipse, some popular camera control software packages had old predicted values for the Earth's rotation. Some due to the authors not updating them, some due to old installations that didn't update the data automatically. That caused people who didn't notice the discrepancy to miss their shots.

[1] https://celestialprogramming.com/julian.html

[2] https://www.iers.org/IERS/EN/Publications/Bulletins/bulletin...