What Is a Leap Year?
A leap year is a calendar year that contains an additional day, making it 366 days long instead of the usual 365. This extra day is added to keep our calendar year synchronized with the astronomical year, or the time it takes for Earth to complete one full orbit around the Sun. The extra day is added as February 29th.
Section 2: Why Do We Need Leap Years?
The Earth takes approximately 365.2422 days to orbit the Sun, which is slightly longer than our standard 365-day calendar year. This small fraction of a day, about a quarter of a day, would cause our calendar to drift out of sync with the seasons over time. Adding an extra day approximately every four years corrects for this discrepancy.
Section 3: The Rules for Leap Years
The rule for determining a leap year is not simply 'every four years.' A year is a leap year if it is divisible by 4, except for end-of-century years, which must also be divisible by 400 to be a leap year. For example, the year 2000 was a leap year because it's divisible by 400, but the year 1900 was not.
Section 4: The Importance of Leap Years
Without leap years, the calendar would become misaligned with the seasons by about 24 days every century. This means that eventually, solstices and equinoxes would shift into different months. Leap years ensure that important dates, like the start of spring, consistently align with the same astronomical events each year.