Our Current Calendar

Our present day calendar keeps track of the solar year. It's a 365 day calendar divided into twelve months: January, February, March, April, May, June, July, August, September, October, November, December. The length of the solar year is actually slightly longer than 365 days, so every now and then we add an extra day to the year to bring our calendar back in sync with the solar year. This way our calendar is at most a day off.

[The formula for determining when to add an extra day to the year is a bit complicated. It goes like this:

  1. Add an extra day every four years.
  2. Every one hundred years we skip a leap year.
  3. Every four hundred years we DO have the leap year that we would normally skip.
So...
  1. Years evenly divisible by 4 are leap years.
  2. Except years evenly divisible by 100 are NOT leap years.
  3. EXCEPT years evenly divisible by 400 which ARE leap years.
Hence the average duration of our present day calendar is 365 + 1/4 - 1/100 + 1/400 = 365.2425 days, which is pretty close to the actual length of the solar year of 365.2422 days. Our present day yearly calendar is only three tenthousandths (0.0003) of a day too long.]

It's interesting to note that there is no year A.D. 0 or 0 B.C.. The years jump from 1 B.C. to A.D. 1.




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