This is this weB log’s first leap day. In case you missed it it is not a common year, this is a leap year. I will assume that everyone knows that about every four years we need to add an extra day into the year to keep our calendar in sync with the astronomical alignment that defines a year. This is all based upon keeping the vernal equinox close to March 21st.
Did you notice that I said about every four years? That choice of words was intentional and the topic of this post.
In the Gregorian calendar (our calendar system), most years that are divisible by 4 are leap years. In a leap year, the month of February has 29 days instead of 28. Adding an extra day to the calendar every four years compensates for the fact that a solar year is almost 6 hours longer than 365 days (almost ¼ day longer). However, some exceptions to this rule are required since the duration of a solar year is slightly less than 365¼ days, which means that adding a full day every four years pushes our calendar ahead of the actual day – ever so slightly every leap year.
Here’s the little known addendum to the rule: Years which are divisible by 100 are not leap years, unless they are also divisible by 400, in which case they are leap years. For example, 1600 and 2000 were leap years, but 1700, 1800 and 1900 were not. Going forward, 2100, 2200, 2300, 2500, 2600, 2700, 2900, and 3000 will not be leap years, but 2400 and 2800 will be. By this rule, the average number of days per year will be 365 + 1/4 – 1/100 + 1/400 = 365.2425, which is 365 days, 5 hours, 49 minutes, and 12 seconds.
However, even this fine tuning introduces an error of about .000125 days per year. Therefore that means that in 8,000 years the calendar will be behind by a day. To top it all off, the exact position of the earth in 8,000 years can’t be predicted to that that kind of accuracy (the Earth is slowing so the day is becoming ever so slightly longer), therefore at some unknown date in the future we’ll have to add an extra day to keep it all in sync.
Way too technical? How about this, what is a person born on a leap day called? A leapling, of course.
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