With today being February 29th, I got to thinking about leap years and how do we keep our calendars in synch with the Earth’s 365.2422 day year? If each Earth year is exactly 365.25 days, problem solved. You just add one extra day every four years. But since that isn’t the case, it can’t be the case that every four years we add a day. Otherwise we would eventually get off. Since every four years there’s been a leap year in my lifetime, I just assumed this was the case.

However, I have since discovered this is not the case! While it is true that typically every four years (1988, 1992, 1996…2016, 2020) an extra day is added on February 29th, there are some cases where a leap year is added less frequently. For example, the years 1800 and 1900 were not leap years while the years 2100, 2200, 2300, and 2500 will not be leap years. So, in truth leap years are a little less frequent than every four years to keep our calendars in synch with the earth’s exact year. Pretty wild!

*Note:* For more on this subject and what Julius Caesar has to do with it, click here.