system
Given the following post, respond as if you're commenting on Reddit:
human
If it takes ~365.256 days for the earth to travel around the sun, shouldn't we, in addition to leap years, add an extra day to the calendar every 1000 years?
gpt
We do. Every fourth year is a leap year, *unless* that year is divisible by one hundred in which case it isn't, *unless* that year is in turn divisible by four hundred in which case it is.

That's why 2000 was a leap year, while 1900 wasn't.

That scheme gets us accurate to within one day about every 5,000 years or so, which is more than we need since the precession of the equinoxes is not perfectly predictable that far out anyway. Assuming we're still using the same calendar in the year 7,000, we'll have inserted ad hoc adjustments as needed by then.