Why Leap Years Are Used

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PostMon Jan 09, 2012 6:16 pm » by Mozi!!a

A leap year in the Gregorian calendar includes an extra day at the end of February. A leap year consists of 366 days, whereas other years, called common years, have 365 days. The extra day, February 29 is the 60th day of a leap year in the Gregorian calendar.
Why are leap years needed?

Leap years are needed to keep our calendar in alignment with the earth's revolutions around the sun.

The next leap year will occur in 2012.


The vernal equinox is the time when the sun is directly above the Earth's equator, moving from the southern to the northern hemisphere.

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.

(The term "day" is used to mean "solar day"–which is the mean time between two transits of the sun across the meridian of the observer.)
Is there a perfect calendar?

No calendars used today are perfect; they are off by seconds, minutes, hours or days every year. To make a calendar more accurate, new leap year rules have to be introduced to the Gregorian calendar, complicating the calculation of the calendar even more. It will, however, need some modifications in a few thousand years. As for the tropical year, it is approximately 365.242199 days, but varies from year to year because of the influence of other planets.
Name of calendar When introduced Average year Approximate error introduced
Gregorian calendar AD 1582 365.2425 days 27 seconds (1 day every 3,236 years)
Julian calendar 45 BC 365.25 days 11 minutes (1 day every 128 years)
365-day calendar - 365 days 6 hours (1 day every 4 years)
Lunar calendar ancient 12-13 moon-months variable

A calendar similar to the Julian calendar, with every fourth year earmarked as a leap year, was first introduced by King Ptolemy III of Egypt in 238 BC.

In ancient times, it was customary to have lunar (moon) calendars, with 12 and/or 13 months every year. To align the calendar with the seasons, the 13th month was inserted as a "leap month" every two or three years. Many countries, especially in Asia still use such calendars. Read more about Leap Year in Other Calendars.

Note: Many other calendars have been and still are used throughout the world.
Why the change from the Julian to the Gregorian calendar?

The Julian calendar introduced too many leap days, thus increasing the number of days between the vernal equinox of March 21, its scheduled date as noted in AD 325 during the Council of Nicaea. The introduction of the Gregorian calendar allowed for realignment with the equinox; however, a number of days had to be dropped when the change was made. Click on any one of the year links below for a better explanation of the calendars and the days that were dropped in order to make the switch to the Gregorian calendar.

The Gregorian calendar was first adopted in Italy, Poland, Portugal and Spain in 1582. This was done by dropping 10 days in October of that year.
.In Great Britain (and America), the Gregorian calendar would not be adopted until much later, in September 1752; 11 days were dropped.
Sweden (and Finland) had a "double" leap year in 1712. Two days were added to February–creating a date of February 30, 1712. (This was done because the leap year in 1700 was dropped and Sweden's calendar was not synchronized with any other calendar. By adding an extra day in 1712, they were back on the Julian calendar.) Read more about February 30
.The Julian calendar is currently (between the years 1901 and 2099) 13 days ahead of the Gregorian calendar (because too many leap years were added).

Other leap years facts

The Gregorian calendar has a 400-year cycle until it repeats the same weekdays for every year–February 29, 2008, is a Friday and February 29, 2408, is a Friday.
The Gregorian calendar has 97 leap years during those 400 years.
The longest time between two leap years is eight years. The last time that occurred was between 1896 and 1904. The next time will be between 2096 and 2104.

Special Leap Years
Leap years that share the same day of week for each date repeat only every 28 years between the years 1904 and 2096. The year 2008 was a leap year. If you look at a 2008 calendar, you will see that February has five Fridays–the month begins and ends on a Friday. February comprised five Fridays in 1980 as well, and the next occurrence will be in 2036. February 29, the leap day, has been associated with age-old traditions, superstitions and folklore.


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PostMon Jan 09, 2012 6:50 pm » by SamueltheLion


leap years are used because there are 5 additional gods on this planet.

a perfect circle is 360°, not 365.

the calendars... zey are skrewed up, just like z earth's wobbol.
Your faith will make you whole

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PostMon Jan 09, 2012 7:02 pm » by TheDuck

Four quater days (365.5) every Four years equals one extra day.

Thread summed up in a sentence. :mrgreen:
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