Eli5 what is the point in leap years ,like why do we have them?
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The Earth takes longer than 365 days to go around the Sun. Currently the 365-day estimate is a little over six hours off. If we just left the year at 365 days, eventually the year would drift away from the cycle of seasons, and eventually January would be in the springtime (or summer, or fall, if you go long enough). But if we went for 366 days each year, the calendar would drift in the opposite direction.
Different calendars handle this differently. Some calendars insert a whole extra month in some years to keep things from drifting too far. The Roman calendar firat tackled this by inserting an extra day every four years, and to this day, most people still think that’s how it works.
But a few hundred years later, we discovered that a day every four years is *slightly* too many: the calendar still drifts. It’s about 3 days too many every 400 years. So they made an exception to the one-every-four rule -years divisible by 100 are not leap years- and an exception to *that* rule: years divisible by 400 *are* leap years. This is why 2000 was a leap year, but more importantly, it brings us to 97 leap days every 400 years, which is very close to the amount we actually need.
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