skuddårsekvens

A skuddårsekvens, or leap year sequence, refers to the recurring pattern of years that are designated as leap years within the Gregorian calendar system. A leap year is a year containing an extra day, February 29th, which is added to keep the calendar year synchronized with the astronomical year. The skuddårsekvens is governed by specific rules to ensure this synchronization.

The primary rule for a skuddårsekvens is that a year is a leap year if it is divisible by four. However, there are exceptions to this rule. Years that are divisible by 100 are generally not leap years, unless they are also divisible by 400. This means that the year 1900 was not a leap year, as it is divisible by 100 but not by 400. Conversely, the year 2000 was a leap year because it is divisible by 400.

This skuddårsekvens creates a cycle of 400 years. Within this 400-year cycle, there are exactly 97 leap years. The standard four-year cycle is interrupted by the century rule, making the actual distribution of leap years slightly more complex than a simple division by four. This precise sequencing ensures that the calendar gradually drifts by less than a day over long periods, maintaining accuracy for seasons and astronomical events. The concept is crucial for fields like astronomy, navigation, and long-term timekeeping.