WHY DO WE NEED LEAP YEARS? Since it takes Earth approximately 365¼ days to orbit the sun, an extra day’s worth of time accumulates every four years. A leap year, February receives an extra day to compensate for the difference between the astronomical year and the calendar year. Egyptian Calendar If no adjustment were made, the calendar and the seasons would drift apart by 24 days every 100 years. The plan of adding a day every four years was devised by the Egyptians. The Romans created a standard leap day, February 29, in 46 B.C. Ancient Roman Calendar Adding one day per four years didn’t perfectly correct the problem, however, because Earth orbits in 11 minutes and 14 seconds less than 365¼ days. A correction, established in 1582, adds a leap day only to century years divisible by 400. Thus 2000 was a leap year, but 2100, 2200, and 2300 will not be. ...