5 ms·
The lunar day is 29.56... days long. Some months, they had 29 days. Some months, they had 30 days. But there's still that pesky .06 days that accumulates over t
by prometheus76 6y ago
The lunar day is 29.56... days long. Some months, they had 29 days. Some months, they had 30 days. But there's still that pesky .06 days that accumulates over time, pushing the calendar out of sync with the astronomical events. In our calendar, we add a leap day every four years to catch that "leakage". They would add a month occasionally, but they did it at random intervals, so sometimes the calendar would have drifted 5 days off the gregorian before they corrected it, and other times it was apparently up to 8 weeks drifted from gregorian time. So the amount of drift was not in lunar month chunks. It was in accumulated drifts of .06, that got corrected at random intervals.
- Retric 6y agoIt’s 29 days 12 hours 44 minutes on average but not every lunar month is identical. Normally lunar calendars alternate 29, 30, 29, 30 days evenly as that pattern is easy to see. Years are more complicated but in 864, Japan adopted one of the Chinese calendars in which a year was defined as 365.2446 which is quite close to the actual 365.2425 days and thus worked fine for long periods. However, the 44 minutes adjustment needs a leap day every ~2.6 years or it obviously drifts out of sync. Adding a full month is pointless because it doesn’t change the offset.