Question

Why is an extra day added to February every for years

Answer 1

February 29 appears every 4 years which is called a leap year. The reason is because the earth does not orbit the sun exactly 365 days. 

Answer 2

February 29 is a date that usually occurs every four years, and is called a leap day. This day is added to the calender in leap years as a measure, because the earth doesnt orbit around the sun in exactly 365 days (1 year). The gregorian calendar is a modification of the julian calender first used by the romans.