By definition a leap year (or intercalary year) is a year containing an extra day or month in order to keep the calendar year in sync with an astronomical or seasonal year which follows the gregorian calendar.

The Gregorian calendar is the standard calendar that is used by most of the world and which in 1582, Pope Gregory XIII made it law that everyone should follow it due to the fact that the julian calendar was to long thus the vernal equinox (Beginning of Spring) kept going backwards due to the Shifting of the earth Rotation.

The Julian Calendar was introduce by Julius Caeser in 46AD to track the tropical year which is how long it takes for the sun (as seen by earth) to return to the same position on the ecliptic (its path among the stars on the celestial sphere).

So how does a leap year work well every 4th year or any year that can be divided by 4 is given an extra day which is February 29th. This also happens every 400 years as well; which happened in 2000. So in 400 years or 2400 AD we will have another leap as well. (just to be clear its only 1 day for the 4 century mark not 2).

So why does it matter that we have a leap year well the follow info will tell you why.



But a interesting thing could possible happen in the year 2800 with the calendar but im still not clear of it after reading it several times though but go to this link though.

http://en.wikipedia.org/wiki/Revised_Julian_calendar

but here is a interesting thought about birthdays that happen on 29th of feb:




To read more about the Leap I recommend these sites:


http://en.wikipedia.org/wiki/Tropical_year
http://en.wikipedia.org/wiki/Gregorian_calendar]Read More about the Gregorian Calender
http://en.wikipedia.org/wiki/Julian_Calendar
http://en.wikipedia.org/wiki/Leap_year
http://en.wikipedia.org/wiki/Revised_Julian_calendar

Very well said. Also leap year has been used i know for hundreds of years. It is to help make sure we keep in track for a year is really should be 365.2 Days Long or something like that. Thanks for this great summary of it. This is very helpfull.

- Mysterio

i didn't get what you meant about every 400 years.

A year is actually 365 days and 6 hours (6x4=24 or 1 day). So every four years, they have to add one extra day. Or else the calender will be messed up in a few thousand year (like summer will actually be in the winter.. this is just an example).

Here will find my answer to DogEater008's question tha is why every 400 we add one day:

It is because The Gregorian calandar gives an average year length of 365.2425 days. And by adding 1 days for each 4 years, we in fact considered the year of length of 365.25 days. instead of 365.2425 days. with difference about .0075 extra. Then when we don't add the leap in the year dividisable by 100, we take of .01 instead of .0075 day with difference .0025 day which can be corrected by add 1 day every 400 years.

Remember that even 365.2425 is different than the exact 365.242375 so all the above has another difference .000125 day which can be corrected every 800 years. This may be the answer to Saint_Michaels question about year 2800.

I kind of had a little idea about leap year before. I knew it was meant to keep us from falling behind. What I did not realize was how recent in history that many countries had actually adopted the calander. I love this kind of thing. Its so facinating. Thank you for sharing.

kinda knew that but propz

That's interesting, I always wondered about that..