Neglecting leap seconds, there are 30 years and *12 hours* between 1 Jan 1970 0:00 (the start of the unix "POSIX" epoch that computers use) and 1 Jan 2000 12:00 (when astronomer's start their "J2000" epoch - yes, astronomers measure things from midday.)

But if you use Julian years, that 12 hours vanishes and the gap becomes exactly 30 Julian years.

This gives me a panic attack every few years when I suddenly refuse to believe it can be true and want to know where those 12 hours have gone. I knows 30 Julian years is right. I know I've checked it before multiple times. And yet I still won't accept it.

So where have they gone? Well, Julian years are 18 hours shorter than a leap year, and 6 hours longer than a regular or "common" year, so every two Julian years the clock shifts by 12 hours.

Hence why I'm writing this thread: in the hope I will now remember this fact, stop doubting myself, and avoid another panic.

And if you thought that was complicated, it gets a lot harder from thereon in...