Why does February have 29 days in a leap year?

1st answer: Because Earth actually takes 365 days and 6 hours to complete its one revolution. So after four years 6 hours change into 24 hours [6*4], meaning 1 day which is added in February as 29th February.

2nd answer: February has 29 days in a leap year for the following reason: A normal year is actually 365 days around 6 hours to be exact 5 hours, 48 minutes and 47 seconds.

To make our calendar system work, we just lump the 6 hours together every 4 years to create the extra day in February, this just happens to be February 29th.

To mange the fact it's not exactly 6 hours for the extra, we adjust for that on the century.

You can use the following algorithm to work out if a year is a leap year or not:

if year is divisible by 400 thenis_leap_year else if year is divisible by 100 then not_leap_year else if year is divisible by 4 then is_leap_year else not_leap_year
The Earth's yearly voyage around the Sun is not an exact number of days - it is 365.2422 days, or about 365 1/4 days. Therefore, to adapt the calendar to the astronomical reality, every 4 years an extra day is added to the year.