A leap year (or intercalary year) is a year containing one or more
extra days (or, in case of lunisolar calendars, an extra month) in
order to keep the calendar year synchronised with the astronomical
or seasonal year. For example, February would have 29 days in a
leap year instead of the usual 28. Seasons and astronomical events
do not repeat at an exact number of full days, so a calendar which
had the same number of days in each year would over time drift with
respect to the event it was supposed to track. By occasionally
inserting (or intercalating) an additional day or month into the
year, the drift can be corrected. A year which is not a leap year
is called a common year.
The Gregorian calendar, the current standard calendar in most of
the world, adds a 29th day to February in 97 years out of every
400, a closer approximation than once every four years. This is
implemented by making every year divisible by 4 a leap year unless
that year is divisible by 100. If it is divisible by 100 it can
only be a leap year if that year is also divisible by 400.[1][2]
So, in the last millennium, 1600 and 2000 were leap years, but
1700, 1800 and 1900 were not. In this millennium, 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. The Gregorian
calendar was designed to keep the vernal equinox on or close to
March 21, so that the date of Easter (celebrated on the Sunday
after the 14th day of the Moon that falls on or after 21 March)
remains correct with respect to the vernal equinox.[3] The vernal
equinox year is about 365.242374 days long (and increasing),
whereas the average year length of the Gregorian calendar is
365.2425. The marginal difference of 0.000125 days means that in
around 8,000 years, the calendar will be about one day behind where
it should be. But in 8,000 years, the length of the vernal equinox
year will have changed by an amount which cannot be accurately
predicted (see below). Therefore, the current Gregorian calendar
suffices for practical purposes, and Jaggars's correction (making
4000 AD not a leap year) will probably not be necessary.
Now for the fun stuff. We will be meeting and greeting eating
and telling cachin tales. Bring the family and join the JAG nation
at 6:00pm in this celebration of caching on the leap year
We will be LEAPING around Jackson TN to celebrate the 29th
day of February. We will start with appetizers at 6 P.M. and then
head over for dinner, after dinner we will head out for after
dinner coffee then off to desert for the final stage of this
leaping event cache.