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 M¢25  Funded By Mahalo ? |  February 24, 2009 12:38 AM

Are there any specials rules about leap years?

Every so often, do leap years get skipped or added on in order to make sure that the calendar is in tune with the Earth's orbit?
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February 24, 2009 01:16 AM
Yes,

In the Gregorian calendar, the current standard calendar in most of the world, most years whose division by 4 equals an integer are leap years. In each 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 period of 365 days is shorter than a solar year by almost 6 hours.

However, some exceptions to this rule are required since the duration of a solar year is slightly less than 365.25 days.
Years that are evenly divisible by 100 are not leap years, unless they are also evenly 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.
Similarly, 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.
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—i.e. a full moon—that falls on or after March 21) remains correct with respect to the vernal equinox.[3] The vernal equinox year is about 365.242374 days long (and increasing).

The marginal difference of 0.000125 days between the Gregorian calendar average year and the actual year means that, in around 8,000 years, the calendar will be about one day behind where it is now. But in 8,000 years, the length of the vernal equinox year will have changed by an amount that cannot be accurately predicted (see below). Therefore, the current Gregorian calendar suffices for practical purposes, and the correction suggested by John Herschel of making 4000 a non-leap year will probably not
Source(s):
"http://en.wikipedia.org/wiki/Leap_year"

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February 24, 2009 12:56 AM
The amount of difference is so small, they don't need to skip a whole year. They added a leap second this year to make up for a small disparity.

http://www.timeanddate.com/date/leapyear.html
"The mean time between two successive vernal equinoxes is called a tropical year–also known as a solar year–and is about 365.2422 days long.

Using a calendar with 365 days every year would result in a loss of 0.2422 days, or almost six hours per year. After 100 years, this calendar would be more than 24 days ahead of the season (tropical year), which is not desirable or accurate. It is desirable to align the calendar with the seasons and to make any difference as insignificant as possible.

By adding a leap year approximately every fourth year, the difference between the calendar and the seasons can be reduced significantly, and the calendar will align with the seasons much more accurately."

There is still a small difference, but nothing that amounts to anything. There is no "perfect" calendar...if memory serves, the Mayan calendar was the closest...

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February 26, 2009 02:37 PM
The reason we get leap years is because each year has 365 and 1/4 days so 4 equals to 366

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