why is there a leap year after every four years?

This is because there arent actually 365 days in a year. It is close to 365.25. So because of that we have to have a full extra day every four years in order to account for the 0.25.

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

The earth actually takes slightly less than 365.25 days to go around the sun. If we don't compensate for the extra time, the seasons will drift against the calendars, until winter would take place in August (in the northern hemisphere).

So, every four years, we add a day. BUT we also need to take back a little time, so if the year is divisible by 100, it's not a leap year. BUT(!) if the year is divisible by 400, it's still a leap year.

So, 1900 was not a leap year, but 2000 was.

The rule is:

If year is evenly divisible by 4, it is a leap year

unless the year is evenly divisible by 100, but not 400.

Earth actually takes 365.25 days to revolve around the sun so every four years .25 factor gets converted to 1 and adds to 365 and makes it 366 days. So after every four years there is a leap year.

Just to complicate it even more, it the Earth takes a little less than 365.25 days to go around the sun, so the last year of the century (1800, 1900 etc.) Doesn't have a leap day unless the year is divisible by 4. So 1600, 2000 and 2400 will have leap days.

Earth actually takes 365.25 days to revolve around the sun(however this has reduced by 1 microsecond due to the recent Tsunami on Dec 26, 2004). so every four years .25 factor gets converted to 1 and adds to 365 and makes it 366 days. So after every four years there is a leap year.

the earth takes 365 1/4 days to complete one revolution of the sun and 1/4 of a day is 6 hours .Therfore every year these 6 hours get accumalated and after 4 years become 1 day or 24 hours.so every 4 years one day is added to the year which is known as a leap year.

The earth revolves around the sun and it takes about 365 and a quarter day for every year. The quarter or the 0.25day is added every fourth year and it is called a leap year

earth actually doesnt take 365 days for revolution....it tales 365.25 days...this is difficult to calculate the period of year...so they considered 365 days in a year..and the rest point 25 days are calculated once in 4 years to constitute the sum of 1 day ...

1/4th day... is point 25 day

so 1/4+1/4+1/4+1/4=1day

so this day is added for every four years..so we get an extra day in that year...this is known as a leap year as it has an extra day

Leap years are needed to keep our calendar in alignment with the earth's revolutions around the sun. The solar year is about 365.2422 days, therefore 365.2422 + 365.2422 + 365.2422 + 365.2422

= 4 (365) + 4(0.2422)

= 1460 + 1

= 1461

That one day is added to february to call it as a leap month and to call the year as leap year.

as earth takes 365.25 days to complete its revolution around the sun therefore after every 4 yrs this .25 makes 1 day which is extra and since february has only 28 days in it therefore this extra day is added there giving us the leap year