February 29th - it’s Leap Day!
Seems like as good a time as any to finally figure out why, exactly, we go around adding days to our calendar.
- The length of a solar year, on which our calendar is based, is 365.242 days, which is about 11 minutes shorter than 365.25 days.
- To compensate for the extra .242th of a day, we add one day to the calendar every 4th year, so every year divisible by 4 becomes a leap year.
- Except: Since the solar year is 365.242 days, and we’re basically making each year exactly 365.25, we’re adding a little extra each year. In fact, adding a day every 4th year adds about 3 extra days over 400 years. So only every 4th century year is a leap year. The year 2000 was a leap year, but 2010 will not be, and 1700, 1800, and 1900 were not leap years. You can determine which century is a leap year if it’s evenly divisible by 400.
Don’t you feel better now? I know I do. Go enjoy your extra day.
