why do we have a leap year every fourth year?

Answer 1

We have leap years because the length of a year is not an exact multiple of the length of a day (because there is no reason for them to match exactly).

Since the remainder of the division is about 1/4, most leap years happen every four years -- arbitrarily, years that are evenly divisible by 4. 2004 was the last one.

Every hundred years, they skip a leap year on a year that is evenly divisible by 100. So there will be no leap year in 2100. However, if the year is evenly divisible by 400, there *IS* a leap year added as a final correction. So there WAS a leap year in 2000.

The last bit of error between the length of a day and the length of a year is corrected by the insertion of "leap seconds". Every few years (I'm not sure how often) the official clocks continue counting past 11:59:59 on December 31 and briefly flash 11:59:60 before they turn over to 12:00:00 on January 1.

Answer 2

Don C's answer was excellent. But we actually
don't have a leap year every fourth year. In
our Gregorian calendar year numbers ending
in 00 are not leap years unless the number
is divisible by 400. Thus 2000 was a leap year
but 2100 won't be one.
This was decreed in 1582
by Pope Gregory to bring our calendar in
better alignment with the solar year.
The Julian calendar was 11 days behind
at that time.

Answer 3

Leap years are needed so that the calendar is in alignment with the earth's motion around the sun.

The mean time between two successive vernal equinoxes is called a tropical year, and it is about 365.2422 days long. This means that it takes 365.2422 days for the earth to make one revolution around the sun (the time is takes to orbit the sun).

Using a calendar with 365 days would result in an error of 0.2422 days or almost 6 hours per year. After 100 years, this calendar would be more than 24 days ahead of the seasons (tropical year), which is not a desirable situation. It is desirable to align the calendar with the seasons, and make the difference as small as possible.

By adding leap years approximately every 4th year, this difference between the calendar and the seasons can be reduced significantly, and the calendar will follow the seasons much more closely than without leap years.

Answer 4

Because a solar year is closer to 365.25 days than 365. We skip leap years 3 times ever 400 years to be more accurate, That was the change from the Julian to the Gregorian calender. There will be no leap years in 2100, 2200, or 2300.

Answer 5

because each year is 365 and a quarter days long. each quarter is placed together on the fourth year in order to make an extra day, which becomes 29th february. the next one is is 2008.

Answer 6

there are 365 and a quarter days in a year. so we make up the 4 quarters (1 day) every 4th year. Thus Feb. 29th, lol.... this is true