Which years are leap years?

Leap years are specific years in the Gregorian calendar that have an extra day added to them, making them 366 days long instead of the usual 365 days. This extra day is added to the month of February, as February 29th. The purpose of a leap year is to account for the fact that the Earth's orbit around the Sun takes about 365.2422 days, which is approximately 365 days and 6 hours.

Divisibility by 4: Most leap years occur in years that are evenly divisible by 4. Keywords: "divisible by 4," "leap year every 4 years."

Exception for Centuries: While every fourth year is a leap year, there's an exception for years that are divisible by 100. Keywords: "leap year exception for centuries," "divisible by 100 leap year."

Exception for Special Centuries: Despite the exception for years divisible by 100, there's another exception for years divisible by 400. Keywords: "leap year exception for special centuries," "divisible by 400 leap year."

Here's the breakdown:

Divisible by 4: Years that are evenly divisible by 4 are leap years. For example: 2004, 2008, 2012, 2016, 2020, etc.

Exception for Centuries: While most years divisible by 4 are leap years, years divisible by 100 are not leap years, unless they are also divisible by 400. This exception helps correct for the slight overestimation in the solar year length. For example:

1700, 1800, and 1900 are not leap years because they are divisible by 100 but not by 400.

1600 and 2000 are leap years because they are divisible by 400.

This system ensures that the average calendar year length remains close to the length of the solar year, helping to keep our calendar in sync with the changing seasons. Leap years help prevent the gradual shift of dates for important events like solstices and equinoxes. The rules for determining leap years provide a structured way to maintain a balance between the calendar and the natural astronomical cycles.